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Is
Matter Around Us Pure
Mixture - Introduction
Matters
can be classified into two types – Pure substances and Impure substances.
Pure
substances – Pure substances
are of two types – Elements and Compounds.
Impure
substances – All mixture are
considered as impure substances.
Most
of the substances in our surroundings are not in their pure form and are called
mixture. Substances which are made of two or more matters and which can be
separated by physical methods are known as mixtures, such as mixture of salt
and water, mixture of sugar and water, mixture of different gases, air, etc.
In
a mixture, components do not combine chemically or through any chemical change.
In a mixture, components do not lose their properties.
Mixtures
are of two types on the basis of their composition - Homogeneous mixture and
Heterogeneous mixture.
Homogeneous Mixture
Mixtures
which have uniform composition throughout are called Homogeneous Mixture. For
example – mixture of salt and water, mixture of sugar and water, air, lemonade,
soda water, etc.
Mixture
of salt in water is an example of homogeneous mixture. In this mixture, the
boundary of salt and water cannot be differentiated. When a ray of light is
passed through the mixture of salt and water, the path of light is not seen.
General Properties of
Homogeneous Mixture:
·All solutions are the examples of homogeneous mixture.
·The particles of a homogeneous mixture are less the one nanometer.
·A homogenous mixture does not show Tyndall effect.
·The boundaries of particles cannot be differentiated.
·The constituent particles of homogenous mixture cannot be
separated using centrifugation or decantation.
·Alloys are the examples of solution.
Heterogeneous Mixture
Mixtures
which do not have uniform composition throughout are called Heterogeneous
Mixture. For example – mixture of soil and sand, mixture of sulphur and iron
fillings, mixture of oil and water etc. The boundaries of constituent particles
of a homogeneous mixture can be identified easily; as a homogeneous mixture has
two or more distinct phases.
General Properties of
Heterogeneous Mixture:
·Most of the mixtures are heterogeneous except solutions and
alloys.
·The constituent particles are present uniformly in a heterogeneous
mixture.
·The components of a heterogeneous mixture can be identified
easily.
·Generally, two or more phases are present in a heterogeneous
mixture.
·Particles of a heterogeneous mixture are sized between one
nanometer and one micrometer or more.
·Heterogeneous mixtures show Tyndall effect.
Types of Mixture
Mixture
can be categorised in three types on the basis of their particles’ size. These
are; solution, suspension and colloid.
Solution:
Mixture
of two or more substances with one phase only, i.e. having no distinct boundary
of constituent particles are called solution. For example, solution of sugar
and water, solution of salt and water, lemonade, soft drinks, etc. Solution is
a homogeneous mixture of two or more substances.
In
a solution, components are mixed in such a way that they appear as only one
phase. Seeing by naked eye, constituent particles of a solution cannot be
identified because particles are mixed evenly throughout.
In
a solution, there are two types of components – one is called solute and other
is called solvent.
Solute – Substance which is present in smaller
quantity in a mixture is called solute.
Solvent – Substance in a mixture which is present
in larger quantity in a mixture is called solvent.
Example:
In the solution of salt and water, salt is present in small quantity while
water is present in larger quantity. Here salt is solute and water is solvent.
Solution
of tincture iodine is made by dissolving iodine in alcohol. In this solution,
iodine is solute and alcohol is solvent.
Air
is mixture of many gases. Since air consists of only one phase, thus it is
considered as solution. Air consists about 78% of nitrogen and 22% rest of
other gases. Thus in the case of air, nitrogen can be called as solvent and
rest other gases as solutes.
Solvent
and solute can be solid, liquid or gas.
Types of solution
Solid
- solid solution – Solution of two
or more solids are generally known as solid-solid solution. For example –
alloys. Alloy is a homogeneous mixture of two or more metals and non metals or
two metals or two non-metals. The components of an alloy cannot be separated by
physical methods, their boundaries are not distinct and they can have variable
compositions, thus alloy is considered as solution.
Solid
– Liquid solution – Solution of
solid and liquid is called solid-liquid solution. For example - solution of
salt and water.
Liquid
– liquid solution – Solution of two
miscible liquids are called liquid-liquid solution, such as solution of water
and acetic acid. The solution of acetic acid in water is known as vinegar.
Gas
- liquid solution – Solution of gas
into liquid is called gas-liquid solution. For example – Soft drink. In soft
drink, carbon dioxide is usually dissolved in liquid, because of which a hiss
sound comes while opening the cap of the bottle.
Gas-gas
solution – Solution of two
or more gas is called gas-gas solution. For example – air, which is the
solution of many gases, such as hydrogen, oxygen, carbon dioxide, etc.
General
Characteristics of Solution:
·Solutions are homogeneous mixture of two or more substances.
·Constituent particles of a solution are mixed evenly throughout.
·There is only one phase in a solution.
·Boundaries of constituent particles cannot be distinguished.
·The size of particles of solution is smaller than one nanometer.
·Solutions do not show Tyndall effect, because, small particles of
solution do not scatter the ray of light.
·Solute cannot be separated by using filtration or decantation.
·Solutions are stable, since when left undisturbed the particles do
not settle in bottom.
Saturated and
Unsaturated Solutions
Saturated
Solution: When a solution
cannot dissolve more solute at a given temperature, the point is called
saturation point of the solution and solution is called saturated solution.
This means, no more solute can be dissolved in a saturated solution at a given
temperature.
Unsaturated
Solution: Solution in which
more solution can dissolved at a given temperature, is called unsaturated
solution.
Solubility: Solubility is the amount of solute in a
saturated solution at a given temperature. In other words, maximum capacity to
dissolve a solute in a solution at a given temperature is called solubility.
Different
solvents can dissolve different amount of solute. This means different solvents
have different solubility Solubility increases with increase in temperature.
Concentration: Concentration is the amount of solute
present in a given amount of solvent or solution.
concentration=Amount of solute/amount of solvent or
concentration=Amount of solute/amount of solution
Thus,
concentration is the ratio of amount of solute and amount of solvent.
Concentration
can be expressed in mass percentage or volume percentage of a solution.
(a) Mass percentage of
a solution
concentration=(mass of solute/mass of solution)*100
This
means when concentration is expressed in mass percentage, it is called
concentration by mass percentage.
(b)
Volume percentage of a solution
concentration=(volume of solute/volume of solution)*100
This
means when concentration is expressed in volume percentage, it is called
concentration by volume percentage.
Separation of
Components of Mixture
Centrifugation –
In
the method of centrifugation, the centripetal and centrifugal forces are used
to separate lighter and heavier components of mixture of two immiscible
liquids. This process is used to separate very small solids particles from a
liquid mixture.
Example
– Milk is the mixture of fat, water, and other constituents. Using the method
of centrifugation, most of the fat can be separated from milk. In milk, fat is
suspended throughout the milk which is separated out using the method of
centrifugation.
When
milk is churned rapidly, water which is heavier than fat, migrates away from
the centre of centrifuge while fat is forced towards the bottom, which is
drained out.
Application
of centrifugation –
·In pathological test of blood and urine.
·In separation of fat from milk.
·In washing machines to squeeze the water from wet clothes.
Decantation –
Decantation
is used to separate the components from a mixture of two immiscible liquids,
such as mixture of oil and water. In a mixture of two immiscible liquids,
lighter one and heavier one form separate layer. The lighter one can be
decanted after settling of mixture, carefully in other container.
In
the process of decantation some of the heavier liquid also poured out with
lighter one. Therefore, components from a mixture of two immiscible liquids;
can be separated more easily and accurately using a separating funnel.
A
separating funnel is usually made of glass with a stop cork with drain pipe at
bottom. The heavier liquid which is settled at bottom is drained out from the
mixture of two immiscible liquids by opening of stop cork from a separating
funnel.
Sublimation
There
are many substances which are converted into gas from solid when heated, and
converted from gas to solid when cooled without converting into liquid. Such
substances are known as sublime. For example – ammonium chloride, naphthalene
balls, camphor, etc. Therefore, mixture of one sublime and other substance can
be separated using the method of sublimation.
The
mixture of ammonium chloride and common salt can be separated out using the
process of sublimation. For this, the mixture is heated in a China dish. The
China dish is covered by an inverted funnel. Cotton is used for plugging the
opening of the funnel. After heating, ammonium chloride is converted into
vapour and gets deposited over the inner surface of funnel; due to cooling.
This leaves the common salt in China dish. Ammonium chloride can be taken out
by scratching from the inner wall of funnel.
Chromatography –
Chromatography
is a method of separation which works on the principle of travel speed of
components of a mixture. This method is used for separating dyes and pigments
from a mixture. Ink is the mixture of dyes of different colours.
There
are many types of chromatography. The dyes from an ink can be separated using
paper chromatography.
For
this, a strip of filter paper is dipped in the ink. Particles of dye start
rising on filter paper; along with water. Different dyes rise with different
speed because of different types of solubility in water and go up to certain
heights.
Application
of chromatography -
·In the separation of colours from a dyes.
·In the separation of pigments from natural colours.
·In the separation of drugs from blood for pathological tests.
Distillation
–
The
process of distillation is used to separate two miscible liquids. The technique
of distillation is based on the difference in boiling points of components of
mixture of miscible liquids. Distillation is to separate the liquids which do
not decompose even upto their boiling points and should boil at more than 250C.
In
the process of distillation, the mixture is heated after keeping in a retort or
distillation flask. The liquid which boils at lower temperature is vaporized at
lower temperature. The vapour so obtained is passed through a tube and gets
condensed in a separate container; leaving liquid with higher boiling point in
the retort or distillation flask.
Distillation
is used to separate the components of the mixture of two miscible liquids that
boils without decomposition and have sufficient difference in their boiling
points.
The
process of distillation is used to purify many liquids, such as water.
Fractional
Distillation
Fractional
distillation is the process of separation of components of mixture into parts
or fraction on the basis of fractional differences in their boiling points.
Fractional
distillation is done when the difference in boiling points of the components of
miscible liquids is less than 250C. In the process of fractional distillation,
a fractional column is used along with retort or distillation flask.
Fractional
column is a tube which contains glass beads, which facilitate surface for the
vapour to cool and condense repeatedly.
Example
– Ethanol and water are separated from their mixture using fractional
distillation. The boiling point of water is 100⁰C while the boiling point of
ethanol is 78.4⁰C. Since the difference of their boiling point is less than
25⁰C, thus they are separated using fractional distillation.
Some
of the Applications of Fractional Distillation:
·In petroleum refineries, petrochemical and chemical plants,
natural gas processing and cryogenic air separation plants.
·In oil refineries to separate crude oil into useful substances (or
fractions).
·In the process of organic juice.
·In the separation of oxygen, liquid nitrogen and argon from air.
Separation
of different gases from air –
Air
comprises of nitrogen, oxygen, carbon dioxide and argon as major components.
Since air is the cheapest source of these gases, thus these are extracted from
air at large scale
After
liquefaction of air by repeated compression and cooling; nitrogen, oxygen,
carbon dioxide and argon are extracted using fractional distillation.
Liquid
nitrogen has boiling point equal to - 190⁰C and thus turns into gas first and
separated from air.
The
boiling point of argon is - 186⁰C, therefore it is extracted after argon.
The
boiling point of oxygen is - 183⁰C, thus it is collected after the extraction
of argon.
Carbon
dioxide turns into solid at a temperature of - 97⁰C, therefore, it is removed
while air is put under liquefaction.
Use
–
Nitrogen
is used as fertilizers, oxygen is used in hospitals and argon is used in bulbs.
Physical
and Chemical Changes
Physical
Change: The change in
which no new substance is formed is called a physical change. During a physical
change, chemical properties do not change but physical properties do change.
Chemical
Change: The change in
which a new substance is formed is called a chemical change. During a chemical
change, chemical properties change.
Pure
Substances
Elements
and Compounds are considered as pure substances.
Elements – Substances that is made of only one
element are called elements, such as hydrogen, carbon, oxygen, silver, gold,
etc.
Compounds – Substances that is made of one or more
elements by chemical combination are called compounds, such as water, carbon
dioxide, copper oxide, hydrochloric acid, etc.
A
compound does not contain the properties of its constituent elements and shows
quite different characteristics.
Magnetic Effect of Electric Current
Properties of magnet:
A free suspended magnet always point towards
north and south direction.
The pole of a magnet which points toward north
direction is called north pole or north seeking.
The pole of a magnet which points toward south
direction is called south pole or south seeking.
Like poles of magnets repel each other while
unlike poles of magnets attract each other.
Similar to other
effects; electric current also produces magnetic effect. The magnetic effect of
electric current is known as electromagnetic effect.
It is observed that when
a compass is brought near a current carrying conductor the needle of compass
gets deflected because of flow of electricity. This shows that electric current
produces a magnetic effect.
Magnetic field and Field Lines
The influence of force
surrounding a magnet is called magnetic field. In the magnetic field, the force
exerted by a magnet can be detected using a compass or any other magnet.
Fig: Magnetic Field Lines
The imaginary lines of
magnetic field around a magnet are called field line or field line of magnet.
When iron fillings are allowed to settle around a bar magnet, they get arranged
in a pattern which mimicks the magnetic field lines. Field line of a magnet can
also be detected using a compass. Magnetic field is a vector quantity, i.e. it
has both direction and magnitude.
Direction
of Field Line: Outside the magnet, the direction of magnetic field line is
taken from north pole to South Pole. Inside the magnet, the direction of
magnetic field line is taken from south pole to north pole.
Strength
of magnetic field: The closeness of field lines shows the relative strength of
magnetic field, i.e. closer lines show stronger magnetic field and vice-versa.
Crowded field lines near the poles of magnet show more strength.
Magnetic field Due to a Current
Carrying Conductor:
Magnetic field due to current
through a straight conductor:
A current carrying
straight conductor has magnetic field in the form of concentric circles; around
it. Magnetic field of current carrying straight conductor can be shown by
magnetic field lines.
The direction of
magnetic field through a current carrying conductor depends upon the direction
of flow of electric current. The direction of magnetic field gets reversed in
case of a change in the direction of electric current.
Let a current carrying
conductor be suspended vertically and the electric current is flowing from
south to north. In this case, the direction of magnetic field will be
anticlockwise. If the current is flowing from north to south, the direction of
magnetic field will be clockwise.
Right Hand Thumb Rule:
The direction of
magnetic field; in relation to direction of electric current through a straight
conductor can be depicted by using the Right Hand Thumb Rule. It is also known
as Maxwell’s Corkscrew Rule.
If a current carrying
conductor is held by right hand; keeping the thumb straight and if the
direction of electric current is in the direction of thumb, then the direction
of wrapping of other fingers will show the direction of magnetic field.
As per Maxwell’s
corkscrew rule, if the direction of forward movement of screw shows the
direction of current, then the direction of rotation of screw shows the
direction of magnetic field.
Properties of Magnetic
Field:
The magnitude; of
magnetic field increases with increase in electric current and decreases with
decrease in electric current.
The magnitude of
magnetic field; produced by electric current; decreases with increase in
distance and vice-versa. The size of concentric circles of magnetic field lines
increases with distance from the conductor, which shows that magnetic field
decreases with distance.
Magnetic field lines are
always parallel to each other.
No two field lines cross
each other.
Magnetic field due to current
through a circular loop:
In case of a circular
current carrying conductor, the magnetic field is produced in the same manner
as it is in case of a straight current carrying conductor.
In case of a circular
current carrying conductor, the magnetic field lines would be in the form of
concentric circles around every part of the periphery of the conductor. Since,
magnetic field lines tend to remain closer when near the conductor, so the
magnetic field would be stronger near the periphery of the loop. On the other
hand, the magnetic field lines would be distant from each other when we move
towards the centre of the current carrying loop. Finally; at the centre, the
arcs of big circles would appear as a straight lines.
The direction of
magnetic field can be identified using Right Hand Thumb’s Rule. Let us assume
that the current is moving in anti-clockwise direction in the loop. In that
case, the magnetic field would be in clockwise direction; at the top of the
loop. Moreover, it would be in anticlockwise direction at the bottom of the
loop.
Clock
Face Rule: A
current carrying loop works like a disc magnet. The polarity of this magnet can
be easily understood with the help of clock face rule. If the current is
flowing in anti-clockwise direction, then the face of the loop shows north
pole. On the other hand, if the current is flowing in clockwise direction, then
the face of the loop shows south pole.
Magnetic
field and number of turns of coil: Magnitude of magnetic field gets summed up
with increase in the number of turns of coil. If there are ‘n’ turns of coil,
magnitude of magnetic field will be ‘n’ times of magnetic field in case of a
single turn of coil.
Magnetic Field due to a current in a
Solenoid:
Solenoid is the coil
with many circular turns of insulated copper wire wrapped closely in the shape
of cylinder.
A current carrying
solenoid produces similar pattern of magnetic field as a bar magnet. One end of
solenoid behaves as the north pole and another end behaves as the south pole.
Magnetic field lines are parallel inside the solenoid; similar to a bar magnet;
which shows that magnetic field is same at all points inside the solenoid.
By producing a strong
magnetic field inside the solenoid, magnetic materials can be magnetized.
Magnet formed by producing magnetic field inside a solenoid is called
electromagnet.
Magnetic Effect of Electric Current
Force on a current carrying conductor in a magnetic
field:
A current carrying conductor exerts a force when
a magnet is placed in its vicinity. Similarly, a magnet also exerts equal and
opposite force on the current carrying conductor. This was suggested by Marie
Ampere, a French Physicist and considered as founder of science of
electromagnetism.
The direction of force over the conductor gets
reversed with the change in direction of flow of electric current. It is
observed that the magnitude of force is highest when the direction of current
is at right angles to the magnetic field.
Fleming’s Left Hand Rule:
If direction of electric
current is perpendicular to the magnetic field, the direction of force is also
perpendicular to both of them. The Fleming’s Left Hand Rule states that if the
left hand is stretched in a way that the index finger, the middle finger and
the thumb are in mutually perpendicular directions; then the index finger and
middle finger of a stretched left hand show the direction of magnetic field and
direction of electric current respectively and the thumb shows the direction of
motion or force acting on the conductor. The directions of electric current,
magnetic field and force are similar to three mutually perpendicular axes, i.e.
x, y and z axes.
Many devices, such as
electric motor, electric generator, loudspeaker, etc. works on the Fleming’s
left Hand Rule.
Electric Motor:
Electrical energy is
converted into mechanical energy by using an electric motor. Electric motor
works on the basis of rule suggested by Marie Ampere and Fleming’s Left Hand
Rule.
In an electric motor, a
rectangular coil is suspended between the two poles of a magnetic field. The
electric supply to the coil is connected with a commutator. Commutator is a
device which reverses the direction of flow of electric current through a
circuit.
When electric current is
supplied to the coil of electric motor, it gets deflected because of magnetic
field. As it reaches the half way, the split ring which acts as commutator
reverses the direction of flow of electric current. Reversal of direction of
current reverses the direction of forces acting on the coil. The change in
direction of force pushes the coil; and it moves another half turn. Thus, the
coil completes one rotation around the axle. Continuation of this process keeps
the motor in rotation.
In commercial motor,
electromagnet; instead of permanent magnet; and armature is used. Armature is a
soft iron core with large number of conducting wire turns over it. Large number
of turns of conducting wire enhances the magnetic field produced by armature.
Electromagnetic Induction
Michael Faraday, an
English Physicist is supposed to have studied the generation of electric
current using magnetic field and a conductor.
When a conductor is set
to move inside a magnetic field or a magnetic field is set to be changing
around a conductor, electric current is induced in the conductor. This is just
opposite to the exertion of force by a current carrying conductor inside a
magnetic field. In other words, when a conductor is brought in relative motion
vis-à-vis a magnetic field, a potential difference is induced in it. This is
known as electromagnetic induction.
Electromagnetic
induction can be explained with the help of Fleming’s Right Hand Rule. If the
right hand is stretched in a way that the index finger, middle finger and thumb
are in mutually perpendicular directions, then the thumb shows the direction of
movement of the conductor, index finger shows the direction of magnetic field
and the middle finger shows the direction of induced current in the conductor.
The directions of movement of conductor, magnetic field and induced current can
be compared to three mutually perpendicular axes, i.e. x, y and z axes.
The mutually
perpendicular directions also point to an important fact that the when the
magnetic field and movement of conductor are perpendicular, the magnitude of
induced current would be maximum.
Electromagnetic
induction is used in the conversion of kinetic energy into electrical energy.
Electric generator:
The structure of
electric generator is similar to that of an electric motor. In case of an
electric generator a rectangular armature is placed within the magnetic field
of a permanent magnet. The armature is attached to wire and is positioned in
way that it can move around an axle. When the armature moves within the
magnetic field an electric current is induced. The direction of induced current
changes, when the armature crosses the halfway mark of its rotation. Thus, the
direction of current changes once in every rotation. Due to this, the electric
generator usually produces alternate current, i.e. AC. To convert an AC
generator into a DC generator, a split ring commutator is used. This helps in
producing direct current.
AC and DC current:
AC – Alternate current:
Current in which direction is changed periodically is called Alternate Current.
In India, most of the power stations generate alternate current. The direction
of current changes after every 1/100 second in India, i.e. the frequency of AC
in India is 50 Hz. AC is transmitted upto a long distance without much loss of
energy is advantage of AC over DC
DC – Direct current:
Current that flows in one direction only is called Direct current.
Electrochemical cells produce direct current.
SUMMATIVE ASSESSMENT –I
SCIENCE (Theory)
Class – X
Time allowed: 3 hours Maximum Marks: 90
General Instructions:
a) All questions are compulsory.
b) The question paper comprises of two sections, A and B. You are to attempt both the sections.
c) Questions 1 to 3 in section A are one mark questions. These are to be answered in one word
or in one sentence.
d) Questions 4 to 6 in section A are two marks questions. These are to be answered in about 30
words each.
e) Questions 7 to 18 in section A are three marks questions. These are to be answered in about
50 words each.
f) Questions 19 to 24 in section A are five marks questions. These are to be answered in about
70 words each.
g) Questions 25 to 27 in section B are 2 marks questions and Questions 28 to 36 are multiple
choice questions based on practical skills. Each question of multiple choice questions is a one
mark question. You are to select one most appropriate response out of the four provided to
you.
Section A
1. What happens when a chemical reaction occurs?
2. Name the two stages of photosynthesis.
3. What is meant by the statement, “Potential difference between points A and B in an electric
field is 1 volt”?
4. (a) What is observed when sulphur dioxide is passed through (i) water, (ii) limewater?
(b) Also write chemical equations for the reactions that takes place.
5. Name the hormone responsible for regulation of:
(i) Metabolism of carbohydrates, fats and proteins.
(ii) Balance of calcium and phosphate.
(iii) Blood pressure.
(iv) Water and electrolytic balance.
6. With the help of neat diagram describe how you can generate induced current in the circuit.
7. Identify the substances oxidized and the substances reduced in the following reactions. Write
the ionic equation for the substances oxidized and reduced.
(a) ( H2 g) + Cl2 (g) ¾¾® 2HCl (g)
(b) ( ) ( ) ( ) ( ) 2 2 H g + CuO s ¾¾® Cu s + H O l
(c) ( ) ( ) ( ) ( ) 2 2 2 H S g + SO g ¾¾® S s + H O l
8. ( ) ( ) ( ) ( ) 4 2 3 2 3 2FeSO s ¾¾® Fe O s + SO g + SO g . Is it a redox reaction or not? If yes, why?
9. (a) Write the formula and chemical name of Bleaching powder.
(b) Write chemical equation to represent the action of atmospheric CO2 gas on bleaching
powder when left exposed in open.
(c) State for what purpose is bleaching powder used in water treatment plants.
10. Mrs. Sharma has gone to the jewelers to buy gold jewellery. She asks the jeweler if the
jewellery is made of pure gold. The jeweler assure her that it is 10% gold and nothing has been
mixed in it. Mrs. Sharma is happy and buys the necklace.
Read the above passage and answer the following questions:
(a) Was the jeweler right in saying that the necklace is made of 100% gold?
(b)What values are promoted by the jeweler?
(c) What precautions should you take while purchasing gold jewellery?
(d)Why does Government insist on purchasing Hallmarked jewellery?
[Value Based Questions]
11. Describe with labelled diagram, the Froth Floatation Process used to separate the gangue from
a Sulphide ore.
12. (a) Draw diagram of a Stomata when it is open.
(b) Label Epidermal cell, Guard cell, Chloroplast and Stomatal opening on the diagram drawn.
13. Write the functions of the following in the digestive process:
(a) Bile
(b) Bicarbonate secreted by the duodenal wall.
(c) Pancreatic amylase.
14. What are ‘hormones’? Write any two functions of hormones.
15. (a) State Ohm’s law.
(b) Draw a schematic diagram of the circuit for studying Ohm’s law.
16. The flow of a current in a circular loop of wire creates a magnetic field at its centre. How many
existence of this field be detected? State the rule which helps to predict the direction of this
magnetic field.
17. (a) Describe the steps involved in obtaining biogas and explain what is meant by anaerobic
decomposition.
(b) Which isotope of Uranium can undergo fission readily?
18. (a) State one limitation of solar energy available from solar cells.
(b) What is the minimum wind velocity required to obtain useful energy with a wind mill.
(c) Define the term ‘Nuclear fission’.
19. Identify the type of chemical reaction taking place in each of the following:
(i) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is
observed.
(ii) On heating copper powder in air in a China dish, the surface of copper powder turns black.
(iii) On heating green coloured ferrous sulphate crystals reddish brown solid is left and small
of a gas having odour of burning sulphur is experienced.
(iv) Iron nails when left dipped in blue copper sulphate solution become brownish in colour
and the blue colour of copper sulphate fades away.
(v) Quick lime reacts vigorously with water releasing a large amount of heat.
Or
During the reaction of some metals with dilute hydrochloric acid, following observations were
made:
(i) Silver metal doesn’t show any change.
(ii) The temperature of reaction mixture rises when aluminium (Al) is added.
(iii) The reaction of sodium metal is found to be highly explosive.
(iv) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
(v) A gas produced when sodium carbonate is added to the acid.
Explain these observations giving suitable reasons.
20. Give reasons for the following:
(a) Metals conduct electricity.
(b)Metals generally do not form compounds with hydrogen.
(c) A piece of zinc placed in blue copper sulphate solution decolourize it.
(d) Alumina is dissolve in molten cryolite for electrolysis to obtain aluminium metal.
(e) Nitrogen gas is used to preserve food.
Or
(a) What is corrosion of metals? Name one metal which does not corrode and one which
corrodes on being kept in atmosphere.
(b) How will you show that the rusting of iron needs oxygen and moisture at the same time.
21. (a) Draw a diagram of human alimentary canal.
(b) Label oesophagus, Liver, Pancreas and Gall bladder on the diagram drawn.
(c) What is the function of enzyme ‘pepsin’ in the digestion process?
Or
(a) Draw a diagram of the human urinary system and label on it:
(i) Kidney (ii) Ureter (iii) Urinary bladder (iv) Urethra
(b) Name the two major components of normal human urine.
22. (a) What is the function of an earth wire in electrical instruments? Why is it necessary to earth
the metallic electric appliances?
(b) Explain what is short circuiting and overloading in an electric supply.
(c) What is the usual capacity of the fuse wire in the line to feed:
(i) Lights and fans?
(ii) Appliances of 2 kW or more power?
Or
(a) State Ohm’s law.
(b) Describe the activity with the help of a diagram to establish the relationship between
current (I) flowing in a conductor and potential difference (V) maintained across its two
ends.
(c) Draw the shape of the curve obtained when a graph is plotted between I and V.
23. (a) What is meant by a magnetic field?
(b) How is the direction of magnetic field at a point determined?
(c) Describe an activity to demonstrate the direction of the magnetic field generated around a
current carrying conductor.
(d) What is the direction of magnetic field at the centre of current carrying circular loop?
Or
(a) What is an electromagnet?
(b) List any of its two uses.
(c) Draw a labelled diagram to show how is an electromagnet made?
(d)What is the purpose of the soft iron core used in making an electromagnet?
24. (a) Distinguish between renewable and non-renewable sources of energy giving one example
of each.
(b) Why is the use of wood as a fuel not advised although forests can be replenished?
Or
Explain why:
(a) It is difficult to burn a piece of wood fresh from a tree.
(b) Pouring dry sand over the fire extinguishes it.
(c) It is difficult to use hydrogen as a source of energy.
(d) Charcoal is considered a better fuel than wood.
Section B
25. In test tube A
(i) the solution turns blue litmus red
(ii) evolves H2 gas with Zn metal
(iii) gives out CO2 on treatment with Na2CO3.
In test tube B
(i) the solution turns red litmus blue,
(ii) liberate H2 with Zn metal and
(iii) does not react with Na2CO3.
What are A and B? Give the chemical reactions involved.
26. (a) In plant, when stomata is opened in night, are called _________.
(b) Justify your answer.
27. Why key used in electric circuit should be kept off? Give reason.
28. The pH of soft drink is _______ and they are _______.
(a) less than 7, acidic (b) more than 7, basic
(c) equal to 7, neutral (d) less than 7, basic
29. Conc. H2SO4 reacts with copper to form a sulphur dioxide gas. In this reaction, conc. H2SO4 act
as a:
(a) Oxidizing agent (b) Reducing agent
(c) Dehydrating agent (d) Bleaching agent
30. What will happen when excess of SO2 is passed through limewater and why:
(a) The solution will become colourless due to formation of Ca(HSO3)2.
(b) Limewater turns milky due to formation of CaSO3.
(c) The solution becomes green due to CaSO3.
(d) The solution becomes pink due to Ca(HSO3)2.
31. Sunlight used for photosynthesis is:
(a) 5% (b) 50% (c) 0.5% (d) 4%
32. The process in which water is split during photosynthesis is called:
(a) Photolysis (b) Hydrolysis (c) Glycolysis (d) None of these
33. Ammeter is always connected in:
(a) Series (b) Parallel
(c) Either in series or parallel (d) Neither in series nor in parallel
34. For current flow one need a:
(a) Closed circuit (b) Source of potential difference
(c) Both (a) and (b) (d) Neither (a) nor (b)
35. A voltmeter connected in parallel to a resistor reads 0.1 volt. There is:
(a) Zero error (b) Positive error (c) Negative error (d) Both (b) & (c)
36. Which of the following is a non-renewable source of energy:
(a) Wood (b) Sun (c) Fossil fuels (d) Wind
Answer
SCIENCE (Theory)
Class – X
(Solutions)
SECTION-A
1. When a chemical reaction occurs, new products are obtained.
2. Light reaction and Dark reaction.
3. Work done to carry a unit positive test charge from A to B is 1 Joule.
4. (a) Sulphurous acid is formed.
SO2 + H2O ¾¾® H2SO3 (Sulphurous acid}
(b) Limewater turns milky due to formation of calcium sulphate.
SO2 + Ca(OH)2 ¾¾® CaSO3 + H2O
5. (i) Thyroxine hormone (ii) Calcitonine hormone
(iii) Adrenaline hormone (iv) Vasopressin hormone
6. Connect a coil AB of wire having a number of turns. Connect it to a sensitive galvanometer as
shown in figure.
Move a bar magnet towards the coil. When North Pole is taken fast towards or South Pole is
taken fast towards the coil, the deflection occurs in the galvanometer but will be in opposite
direction. When the coil and magnet both are stationary, there is no deflection in the
galvanometer. Thus the motion of a magnet, with respect to the coil, produces an induced
potential difference which sets up an induced electric current in the circuit.
7. (a) 2 H ¾¾®2H+ + 2e- (Oxidation)
Substance getting oxidized is H2.
2 Cl + 2e- ¾¾®2Cl- (Reduction)
Substance getting reduced is Cl2.
(b) -
Cu2+ + 2e- ¾¾®Cu (Reduction)
Substance getting reduced is Cu.
2 H ¾¾®2H+ + 2e- (Oxidation)
Substance getting oxidized is H2.
(c) 2
2 2S - ¾¾®2S + 4e- (Oxidation)
Substance getting oxidized is H2S.
S4+ + 4e- ¾¾®S (Reduction)
Substance getting reduced is SO2.
8. It is a redox reaction because Ferrous (Fe2+ ) is getting oxidized to Ferric (Fe3+ ) whereas 2
4 SO -
is getting reduced to 2 SO .
9. (a) CaOCl2, Calcium oxychloride
(b) CaOCl2 + CO2 ¾¾® CaCO3 + Cl2
(c) It is used as disinfectant in water treatment plants.
10. (a) No, he was wrong. Pure gold is very soft and is therefore not suitable for making jewellery.
It is alloyed with either silver or copper to make it hard. But sometimes jewelers mix a large
quantity of copper and silver in gold to earn more profit.
(b) Untrustworthiness, cleverness.
(c) We should always purchase the gold jewellery from a branded shop with proper receipt
and Hallmark certificate.
(d) Government insists on purchasing Hallmarked jewellery as it contains the gold and its
alloyed metal (i.e. copper or silver) in a fixed ratio.
CBSE Sample Paper-01 (solved)
SUMMATIVE ASSESSMENT –I
SCIENCE (Theory)
Class – X
Time allowed: 3 hours Maximum Marks: 90
General Instructions:
a) All questions are compulsory.
b) The question paper comprises of two sections, A and B. You are to attempt both the sections.
c) Questions 1 to 3 in section A are one mark questions. These are to be answered in one word
or in one sentence.
d) Questions 4 to 6 in section A are two marks questions. These are to be answered in about 30
words each.
e) Questions 7 to 18 in section A are three marks questions. These are to be answered in about
50 words each.
f) Questions 19 to 24 in section A are five marks questions. These are to be answered in about
70 words each.
g) Questions 25 to 27 in section B are 2 marks questions and Questions 28 to 36 are multiple
choice questions based on practical skills. Each question of multiple choice questions is a one
mark question. You are to select one most appropriate response out of the four provided to
you.
Section A
1. What happens when a chemical reaction occurs?
2. Name the two stages of photosynthesis.
3. What is meant by the statement, “Potential difference between points A and B in an electric
field is 1 volt”?
4. (a) What is observed when sulphur dioxide is passed through (i) water, (ii) limewater?
(b) Also write chemical equations for the reactions that takes place.
5. Name the hormone responsible for regulation of:
(i) Metabolism of carbohydrates, fats and proteins.
(ii) Balance of calcium and phosphate.
(iii) Blood pressure.
(iv) Water and electrolytic balance.
6. With the help of neat diagram describe how you can generate induced current in the circuit.
7. Identify the substances oxidized and the substances reduced in the following reactions. Write
the ionic equation for the substances oxidized and reduced.
(a) ( H2 g) + Cl2 (g) ¾¾® 2HCl (g)
(b) ( ) ( ) ( ) ( ) 2 2 H g + CuO s ¾¾® Cu s + H O l
(c) ( ) ( ) ( ) ( ) 2 2 2 H S g + SO g ¾¾® S s + H O l
8. ( ) ( ) ( ) ( ) 4 2 3 2 3 2FeSO s ¾¾® Fe O s + SO g + SO g . Is it a redox reaction or not? If yes, why?
9. (a) Write the formula and chemical name of Bleaching powder.
(b) Write chemical equation to represent the action of atmospheric CO2 gas on bleaching
powder when left exposed in open.
(c) State for what purpose is bleaching powder used in water treatment plants.
10. Mrs. Sharma has gone to the jewelers to buy gold jewellery. She asks the jeweler if the
jewellery is made of pure gold. The jeweler assure her that it is 10% gold and nothing has been
mixed in it. Mrs. Sharma is happy and buys the necklace.
Read the above passage and answer the following questions:
(a) Was the jeweler right in saying that the necklace is made of 100% gold?
(b)What values are promoted by the jeweler?
(c) What precautions should you take while purchasing gold jewellery?
(d)Why does Government insist on purchasing Hallmarked jewellery?
[Value Based Questions]
11. Describe with labelled diagram, the Froth Floatation Process used to separate the gangue from
a Sulphide ore.
12. (a) Draw diagram of a Stomata when it is open.
(b) Label Epidermal cell, Guard cell, Chloroplast and Stomatal opening on the diagram drawn.
13. Write the functions of the following in the digestive process:
(a) Bile
(b) Bicarbonate secreted by the duodenal wall.
(c) Pancreatic amylase.
14. What are ‘hormones’? Write any two functions of hormones.
15. (a) State Ohm’s law.
(b) Draw a schematic diagram of the circuit for studying Ohm’s law.
16. The flow of a current in a circular loop of wire creates a magnetic field at its centre. How many
existence of this field be detected? State the rule which helps to predict the direction of this
magnetic field.
17. (a) Describe the steps involved in obtaining biogas and explain what is meant by anaerobic
decomposition.
(b) Which isotope of Uranium can undergo fission readily?
18. (a) State one limitation of solar energy available from solar cells.
(b) What is the minimum wind velocity required to obtain useful energy with a wind mill.
(c) Define the term ‘Nuclear fission’.
19. Identify the type of chemical reaction taking place in each of the following:
(i) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is
observed.
(ii) On heating copper powder in air in a China dish, the surface of copper powder turns black.
(iii) On heating green coloured ferrous sulphate crystals reddish brown solid is left and small
of a gas having odour of burning sulphur is experienced.
(iv) Iron nails when left dipped in blue copper sulphate solution become brownish in colour
and the blue colour of copper sulphate fades away.
(v) Quick lime reacts vigorously with water releasing a large amount of heat.
Or
During the reaction of some metals with dilute hydrochloric acid, following observations were
made:
(i) Silver metal doesn’t show any change.
(ii) The temperature of reaction mixture rises when aluminium (Al) is added.
(iii) The reaction of sodium metal is found to be highly explosive.
(iv) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
(v) A gas produced when sodium carbonate is added to the acid.
Explain these observations giving suitable reasons.
20. Give reasons for the following:
(a) Metals conduct electricity.
(b)Metals generally do not form compounds with hydrogen.
(c) A piece of zinc placed in blue copper sulphate solution decolourize it.
(d) Alumina is dissolve in molten cryolite for electrolysis to obtain aluminium metal.
(e) Nitrogen gas is used to preserve food.
Or
(a) What is corrosion of metals? Name one metal which does not corrode and one which
corrodes on being kept in atmosphere.
(b) How will you show that the rusting of iron needs oxygen and moisture at the same time.
21. (a) Draw a diagram of human alimentary canal.
(b) Label oesophagus, Liver, Pancreas and Gall bladder on the diagram drawn.
(c) What is the function of enzyme ‘pepsin’ in the digestion process?
Or
(a) Draw a diagram of the human urinary system and label on it:
(i) Kidney (ii) Ureter (iii) Urinary bladder (iv) Urethra
(b) Name the two major components of normal human urine.
22. (a) What is the function of an earth wire in electrical instruments? Why is it necessary to earth
the metallic electric appliances?
(b) Explain what is short circuiting and overloading in an electric supply.
(c) What is the usual capacity of the fuse wire in the line to feed:
(i) Lights and fans?
(ii) Appliances of 2 kW or more power?
Or
(a) State Ohm’s law.
(b) Describe the activity with the help of a diagram to establish the relationship between
current (I) flowing in a conductor and potential difference (V) maintained across its two
ends.
(c) Draw the shape of the curve obtained when a graph is plotted between I and V.
23. (a) What is meant by a magnetic field?
(b) How is the direction of magnetic field at a point determined?
(c) Describe an activity to demonstrate the direction of the magnetic field generated around a
current carrying conductor.
(d) What is the direction of magnetic field at the centre of current carrying circular loop?
Or
(a) What is an electromagnet?
(b) List any of its two uses.
(c) Draw a labelled diagram to show how is an electromagnet made?
(d)What is the purpose of the soft iron core used in making an electromagnet?
24. (a) Distinguish between renewable and non-renewable sources of energy giving one example
of each.
(b) Why is the use of wood as a fuel not advised although forests can be replenished?
Or
Explain why:
(a) It is difficult to burn a piece of wood fresh from a tree.
(b) Pouring dry sand over the fire extinguishes it.
(c) It is difficult to use hydrogen as a source of energy.
(d) Charcoal is considered a better fuel than wood.
Section B
25. In test tube A
(i) the solution turns blue litmus red
(ii) evolves H2 gas with Zn metal
(iii) gives out CO2 on treatment with Na2CO3.
In test tube B
(i) the solution turns red litmus blue,
(ii) liberate H2 with Zn metal and
(iii) does not react with Na2CO3.
What are A and B? Give the chemical reactions involved.
26. (a) In plant, when stomata is opened in night, are called _________.
(b) Justify your answer.
27. Why key used in electric circuit should be kept off? Give reason.
28. The pH of soft drink is _______ and they are _______.
(a) less than 7, acidic (b) more than 7, basic
(c) equal to 7, neutral (d) less than 7, basic
29. Conc. H2SO4 reacts with copper to form a sulphur dioxide gas. In this reaction, conc. H2SO4 act
as a:
(a) Oxidizing agent (b) Reducing agent
(c) Dehydrating agent (d) Bleaching agent
30. What will happen when excess of SO2 is passed through limewater and why:
(a) The solution will become colourless due to formation of Ca(HSO3)2.
(b) Limewater turns milky due to formation of CaSO3.
(c) The solution becomes green due to CaSO3.
(d) The solution becomes pink due to Ca(HSO3)2.
31. Sunlight used for photosynthesis is:
(a) 5% (b) 50% (c) 0.5% (d) 4%
32. The process in which water is split during photosynthesis is called:
(a) Photolysis (b) Hydrolysis (c) Glycolysis (d) None of these
33. Ammeter is always connected in:
(a) Series (b) Parallel
(c) Either in series or parallel (d) Neither in series nor in parallel
34. For current flow one need a:
(a) Closed circuit (b) Source of potential difference
(c) Both (a) and (b) (d) Neither (a) nor (b)
35. A voltmeter connected in parallel to a resistor reads 0.1 volt. There is:
(a) Zero error (b) Positive error (c) Negative error (d) Both (b) & (c)
36. Which of the following is a non-renewable source of energy:
(a) Wood (b) Sun (c) Fossil fuels (d) Wind
Answer
SCIENCE (Theory)
Class – X
(Solutions)
SECTION-A
1. When a chemical reaction occurs, new products are obtained.
2. Light reaction and Dark reaction.
3. Work done to carry a unit positive test charge from A to B is 1 Joule.
4. (a) Sulphurous acid is formed.
SO2 + H2O ¾¾® H2SO3 (Sulphurous acid}
(b) Limewater turns milky due to formation of calcium sulphate.
SO2 + Ca(OH)2 ¾¾® CaSO3 + H2O
5. (i) Thyroxine hormone (ii) Calcitonine hormone
(iii) Adrenaline hormone (iv) Vasopressin hormone
6. Connect a coil AB of wire having a number of turns. Connect it to a sensitive galvanometer as
shown in figure.
Move a bar magnet towards the coil. When North Pole is taken fast towards or South Pole is
taken fast towards the coil, the deflection occurs in the galvanometer but will be in opposite
direction. When the coil and magnet both are stationary, there is no deflection in the
galvanometer. Thus the motion of a magnet, with respect to the coil, produces an induced
potential difference which sets up an induced electric current in the circuit.
7. (a) 2 H ¾¾®2H+ + 2e- (Oxidation)
Substance getting oxidized is H2.
2 Cl + 2e- ¾¾®2Cl- (Reduction)
Substance getting reduced is Cl2.
(b) -
Cu2+ + 2e- ¾¾®Cu (Reduction)
Substance getting reduced is Cu.
2 H ¾¾®2H+ + 2e- (Oxidation)
Substance getting oxidized is H2.
(c) 2
2 2S - ¾¾®2S + 4e- (Oxidation)
Substance getting oxidized is H2S.
S4+ + 4e- ¾¾®S (Reduction)
Substance getting reduced is SO2.
8. It is a redox reaction because Ferrous (Fe2+ ) is getting oxidized to Ferric (Fe3+ ) whereas 2
4 SO -
is getting reduced to 2 SO .
9. (a) CaOCl2, Calcium oxychloride
(b) CaOCl2 + CO2 ¾¾® CaCO3 + Cl2
(c) It is used as disinfectant in water treatment plants.
10. (a) No, he was wrong. Pure gold is very soft and is therefore not suitable for making jewellery.
It is alloyed with either silver or copper to make it hard. But sometimes jewelers mix a large
quantity of copper and silver in gold to earn more profit.
(b) Untrustworthiness, cleverness.
(c) We should always purchase the gold jewellery from a branded shop with proper receipt
and Hallmark certificate.
(d) Government insists on purchasing Hallmarked jewellery as it contains the gold and its
alloyed metal (i.e. copper or silver) in a fixed ratio.
11. Sulphide ore is mixed with water and pine oil. The mixture is agitated (shaken vigorously) with
the help of stirrer in the blast of air. Froth is formed, sulphide ore gets attracted towards pine
oil in the froth which is skimmed off, dried and concentrated sulphide ore is obtained. Gangue
is left behind at the bottom of water.
12.
13. The functions of the following in the digestive process are:
(a) Bile: Bile in the duodenum emulsifies fat present in the food, i.e. breaks fat molecules into
small globules.
(b) Bicarbonate secreted by the duodenal wall: Bicarbonate ions secreted by the duodenal
wall mke the medium alkaline because such a medium is required for the action of
pancreatic enzymes.
(c) Pancreatic amylase: Pancreatic amylase acts on starch and hydrolyses it into maltose and
isomaltose.
14. ‘Hormones’ are chemical substances secreted in trace amounts by specialized tissues called
endocrine glands.
The two functions of hormones are as follows:
(i) Hormones coordinate the activities of the body and also its growth.
(ii) Hormones regulate many functions like metabolism and reproduction in our body.
15. (a) Ohm’s law: Under similar physical conditions, such as temperature remains constant, the
current flowing through a wire is directly proportional to the difference in potential
applied across its ends, i.e., I µ V. or V = IR where R is the resistance offered.
(b)
16. To detect the presence of the magnetic field created by the current in a circular loop at the
centre, one can draw the magnetic field lines with the help of compass needle. The magnetic
field lines appear as a straight line at the centre and other lines appear in the same direction
without the loop.
Right hand thumb rule: Hold the wire in your right hand with your extended thumb pointing in
the direction of current. Your folded fingers will indicate the direction of magnetic field around
the wire.
17. (a) Anaerobic decomposition: The process in which the complex compound of cow dung
slurry decomposes or breaks down in the absence of oxygen by anaerobic micro organisms
called anaerobic bacteria is known as anaerobic decomposition.
Steps involved in obtaining biogas:
(i) Slurry is made by mixing of animal dung with an equal amount of water.
(ii) Slurry is passed through an inlet chamber of an underground digester tank.
(iii) In digester tank, slurry is decomposed by anaerobic bacteria in about 50-60 days to
produce biogas.
(iv) The biogas collected in domes built over the digester tank and has a gas outlet with
valve.
(v) The pressure exerted by the biogas on the slurry forces the spent slurry to the
overflow tank via outlet chamber.
(vi) The spent slurry is periodically removed and used as a good manure.
(vii)The whole process is repeated again for regular supply of biogas.
(b) 235
92 U can undergo fission readily.
18. (a) Conversion efficiency is less.
(b) Approximately 15 km/h.
(c) The process in which the heavy Uranium nucleus splits into lighter nuclei of smaller atomic
numbers is called Nuclear fission.
235 1 141 92 1
92 0 56 36 0 U + n ¾¾® Ba + Kr + 3 n + Q
Q refers to the energy of 200 MeV released.
19. (a) Double displacement reaction, precipitation reaction.
(b) Combination reaction, oxidation reaction.
(c) Thermal decomposition
(d) Displacement reaction
(e) Combination and exothermic reaction
Or
(i) Silver is very less reactive metal. So it does not react with dilute HCl.
(ii) The reaction of Al with dilute HCl is exothermic i.e. heat is produced in the reaction, so the
temperature of the reaction mixture rises.
(iii) Sodium is a very reactive metal. It react vigorously with the evolution of heat too.
(iv) Bubbles are seen due to the evolution of H2 gas.
( ) ( ) ( ) 2 2 Pb s + 2HCl aq ¾¾® PbCl + H g
(v) CO2 gas is produced when Na2CO3 reacts with dilute HCl.
( ) ( ) ( ) ( ) ( ) 2 3 2 2 Na CO s + 2HCl aq ¾¾® 2NaCl aq + H O l + CO g
20. (a) It is due to presence of free electrons.
(b) Metals are good reducing agents and H2 is weak oxidizing agent therefore, metals do not
react with hydrogen to form hydrides.
(c) Zn + CuSO4 ¾¾® ZnSO4 + Cu
It is due to formation of ZnSO4 (aq) which is colourless.
(d) It increases electrical conductivity and molten cryolite acts as a solvent.
(e) It prevents oxidation of food which prevents its spoilage.
Or
(a) Corrosion of metal is a process in which metal reacts with substances present in
atmosphere to form surface compounds. ‘Al’ does not corrode whereas ‘Fe’ corrodes when
placed in atmosphere.
(b) Take three test tubes and put iron nails in each of them. In the first test tube add H2O up to
brim and leave no space for air. In the second test tube add fused CaCl2 so as to absorb
moisture. In the third test add water and leave space for air. Leave them for few days.
Rusting will not take place in first and second test tubes. But rusting will take place in third
test tube showing that rusting of iron requires both air and moisture.
21.
(c) The function of the enzyme ‘pepsin’ in the digestion process is that it breaks down proteins
into peptones in acidic medium of gastric juice.
Or
(i)
(ii) The two major components of normal human urine are water and nitrogenous
substances, most of which is urea.
22. (a) The earth wire helps us by offering a low resistance path to the high potential that might
have come in contact with the body or other unwanted part of the device. This will not
bring any damage to the device or to the person handling the device. The fuse may
disconnect the electrical link in such cases.
(b) Overloading is the situation which causes a sudden draw of larger current by the electrical
appliances, when operated at the same time from a single parallel connection.
In short-circuit the live wire comes in contact with the neutral line. This gives a large drop
of potential and flow or current through the fuse wire. So it burns.
(c) (i) 5 A (ii) 15 A
Or
(a) Ohm’s law: The electrical current (I) flowing through a metallic wire is directly
proportional to the potential difference (V) across its ends provided the physical conditions
like temperature remains constant.
Mathematically: V µ I ⇒ V = IR
(b) Aim: To establish the relationship between potential difference across the resistor and
current passing through it.
Apparatus required: Nichrome or eureka wire (length 0.5 m) , an ammeter, a voltmeter
and four cells if 1.5 V each.
Procedure:
(i) Set the circuit as shown in the figure.
(ii) First use only one cell as the source and note the reading of the ammeter and
voltmeter.
(iii) Now connect two cells in series and note the reading of the ammeter and voltmeter
again.
(iv) Now connect three cells in series in the circuit and again take the reading of both
devices.
(v) Lastly connect fourth cell in series in the circuit also note the reading of the ammeter
and voltmeter again.
Observation: In this activity, we will observe that the current increases with potential
difference, i.e. more cells being connected in series. We will get approximately the same
value for
V
I
in each case and we will also obtain straight line graph of V vs I passing
through the origin as shown in figure. From the graph, we observe that
V
I
= constant, i.e. V = constant x I or V µ I
Conclusion: The constant is called Resistance. If we change the wire, the graph will vary
but remain a line with a different slope/resistances.
(c) Shape of the V-I curve is a straight line passing through the origin as shown in figure.
23. (a) Magnetic field: Surrounding a magnet its influence is felt by any other magnetic element. It
may be an attractive of a repulsive influence.
(b) The direction of magnetic field at a point is determined by drawing a tangent at that point.
The direction of tangent gives the direction of magnetic field.
(c) Aim: To demonstrate the direction of the magnetic field generated around a current
carrying conductor.
Procedure:
(i) Obtain the concentric circles pattern of iron fillings around the copper wire by flowing
current through it as shown.
(ii) Place a magnetic needle (compass) at any point (P) over a circle.
(iii) Observe the direction of needle.
(iv) Show the direction by arrows.
Conclusion: The direction of the north pole of the compass needle would give the direction
of the field lines produced by the electric current through the straight wire at that point.
(d) The direction of the field is perpendicular to the plane of the coil and directed inwards for
the clockwise current flowing. For anticlockwise current, it will be outwards.
Or
(a) Magnetizing a material: When a material like soft iron, is placed inside a coil carrying
current (may be a solenoid), it will get magnetized. Once the current is put-off, the
magnetic field will also be lost. Such magnets are called electromagnets.
(b) Two uses of electromagnet:
(i) In electric bells.
(ii) For sorting scrap metal.
(c)
(d) The purpose of soft iron core used in making an electromagnet that:
(i) It is temporary magnetized.
(ii) It retains magnetism as long as current flow is maintained.
(iii) It will ensure an uniform and stronger field.
24. (a) Renewable sources of energy are those that can be used without depleting their reserves
and do not get exhausted. E.g., solar energy, wind energy, hydro energy etc.
Non-renewable sources of energy are those which cannot be replenished and exhausted
with the passage of time, e.g. coal, petroleum and natural gas.
(b) Wood is not advisable used as a fuel, although forests can be replenished due to the
following reasons:
(i) Burning of wood causes pollution.
(ii) The left-over residue after combustion have a disposed off problem.
(iii) Smoke produced by burning of wood causes health hazard.
(iv) Wood is a less heat generating fuel.
(v) Trees are essential for our life as they absorb CO2 and give out O2.
Or
(a) It is because a piece of fresh wood is not dry and therefore it is to be heated at high
temperature before it catches fire that is why it is difficult to burn.
(b) It cuts off the supply of air (oxygen) which is required for combustion to take place.
(c) Hydrogen is highly combustible and burns with an explosion, therefore, it is difficult to
store and transport.
(d) Charcoal, has higher calorific value than wood and produces less smoke than wood.
25. ‘A’ is HCl because it turns blue litmus red and liberates H2 with Zinc and CO2 with Na2CO3.
Zn + 2 HCl ¾¾® ZnCl2 + H2
Na2CO3 + 2HCl ¾¾® 2NaCl + CO2 + H2O
‘B’ is NaOH because it turns red litmus blue and liberates H2 gas with Zinc metal.
Zn + 2 NaOH ¾¾® Na2ZnO2 + H2
Na2CO3 + NaOH ¾¾® No reaction
26. (a) Scotoactive
(b) Due to deficiency of oxygen, in most plants, stomata opens at night, e.g., Opuntia,
Bryophyllum.
27. Key used in electric circuit should be kept off to avoid heating of the resistor because heating
changes resistance.
28. (a)
29. (a)
30. (a)
31. (a)
32. (a)
33. (a)
34. (c)
35. (b)
36. (c)
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Atoms and Molecules
Laws of Chemical Combinations
Before Dalton concept of atom was mere
philosophical. Dalton explained about atom on the basis of Laws of Chemical
Combinations.
There are three laws of chemical combination.
Law of Conservation of Mass
Antoine L. Lavoisier, a French scientist,
established the theory of Law of Conservation of Mass.
The law of conservation of mass states, “Mass
can neither be created nor destroyed in a chemical reaction”.
According to this law mass of an isolated
system will remain constant over time. This means when mass is enclosed in a
system and none is allowed in or out, its quantity will never change. That is
mass will be conserved, and hence this is called Law of Conservation of Mass.
This means total mass of products is always equal to the total mass of
reactants. As there is no loss of mass of substances, i.e. mass is conserved,
that’s why Lavoisier called this the law of conservation of mass.
Reactants and Products:
In a chemical reaction the substances that
combine or react are known as reactants and the new substance/substances
formed are called product or products.
A chemical reaction can be represented in
general as follows:
Example:
When calcium oxide is dissolved in water
calcium hydroxide is formed. The reaction invole in this can be written as:
In this reaction calcium oxide and water are
reactants while calcium hydroxide is product.
In this reaction 74 g of calcium hydroxide is
obtained when 56 g of calcium oxide reacts with 18 g of water, which is
proved by experiment.
Here the total mass of reactants, i.e. calcium
oxide and water is equal to 74 g. And the mass of product, i.e. calcium
hydroxide is also equal to 74g. This proves that the total mass of reactants
is always equal to the total mass of product, which proves the Law of
Conservation of Mass.
Law of Constant Proportions
Law of Constant Proportion states that a
chemical compound always contains exactly the same proportion of elements by
mass.
This law is also known as Law of definite
proportions. Joseph Louis Proust gave this law hence, this law is also known
as Proust’s Law.
Explanation of the law:-
Compounds are formed by the combination of two
or more elements. In a compound the ratio of the atoms or element by mass
remains always same irrespective of the source of compound. This means a
certain compound always formed by the combination of atoms in same ratio by
mass. If the ratio of mass of constituent atoms will be altered the new
compound is formed.
Examples:-
Water is formed by the combination of hydrogen
and oxygen. The ratio of masses of hydrogen and oxygen is always in 1:8 in
water irrespective of source of water. Whether you collect the water from a
well, river, pond or from anywhere the ratio of their constituent atoms by
mass will always same.
Nitrogen dioxide is a compound, which is
formed by the combination of nitrogen and oxygen. The ratio of nitrogen and
oxygen by mass in nitrogen dioxide is in 7:16.
Nitrous oxide is a compound which is also
formed by the combination of nitrogen and oxygen. The ratio of nitrogen and
oxygen in nitrous oxide is in 28:16.
Nitric oxide is a compound, which is also
formed by the combination of nitrogen and oxygen. The ratio of nitrogen and
oxygen in nitric oxide is in 7:8.
From the above three examples it is clear that
if the ratio of the atoms by mass is altered then the new compound is formed,
such as in the case of nitrogen dioxide, nitrous oxide, nitric oxide. These three
compounds are formed by the combination of same atoms but because of
combination of the constituent atoms in different ratios by mass new compound
is formed.
Dalton’s Atomic Theory
John Dalton, a British Chemists and scientists
gave the Atomic Theory in 1808. This theory is popularly known as Dalton’s
Atomic Theory in the honour of John Dalton. He gave the theory on the basis
of Laws of Chemical Combination and explains them properly. In his theory he
explains about atom.
Main postulates of Dalton's atomic theory
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Atoms:
On the basis of
Dalton’s Atomic On the basis of Dalton’s Atomic Theory atom can be
defined as the smallest particles of matter are called atoms.
Other characteristics
of atoms:
- Atom is the smallest particle of matter.
- AAll elements are made of tiny particles called atom.
- Atoms are very small in size and cannot be seen through
naked eyes.
- Atom does not exist in free-state in nature. But atom
takes part in a chemical reaction.
- The properties of a matter depend upon the characteristics
of atoms.
- Atoms are the building block of an element similar to a
brick which combine together to make a building.
- The size of atoms is indicated by its radius.
- In
ancient time atoms was considered indivisible.
Symbols of Atoms of Elements
For convenience elements
are represented by unique symbols. For example: Hydrogen is represented by ‘H’.
Oxygen is represented ‘O’. Nitrogen is represented by ‘N’. Iron is represented
by ‘Fe’. ments are represented by unique symbols. For example: Hydrogen is represented
by ‘H’. Oxygen is represented ‘O’. Nitrogen is represented by ‘N’. Iron is
represented by ‘Fe’.
His worked proved as
boon to science. For his marvelous work Berzilius, together with John Dalton,
Antoine Lavoisier, and Robert Boyle is considered as the Father of Modern
Chemistry.
Symbol of many elements
are taken from their English name, while symbol of many elements are taken from
their Greek or Latin names.
Symbol of some element
which are derived from their Latin name
Several elements are
named after the place where they discovered, such as ‘Copper’ which was taken
from Cyprus. Some elements are named after their colour, such as ‘Gold’ which
means yellow.
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Atomic Mass
Mass of atom is called atomic mass. Since,
atoms are very small consequently actual mass of an atom is very small. For
example the actual mass of one atom of hydrogen is equal to 1.673 x 10-24 g.
This is equal to 0.000000000000000000000001673 gram. To deal with such small
nuber is very difficult. Thus for convenience relative atomic mass is used.
Carbon-12 is considered as unit to calculate
atomic mass. Carbon-12 is an isotope of carbon. The relative mass of all
atoms are found with respect to C-12.
One atomic mass = 1/12 of the mass of one atom
of C-12.
Thus atomic mass is the relative atomic mass
of an atom with respect to 1/12th of the mass of carbon-12
atom. ‘amu’ is the abbreviation of Atomic mass unit, but now it is denoted
just by ‘u’.
The atomic mass of hydrogen atom = 1u.
This means one hydrogen atom is 1 times
heavier than 1/12th of the carbon atom.
The atomic mass of oxygen is 16u, this means
one atom of oxygen is 16 times heavier than 1/12th of carbon
atom.
Absolute mass or Actual atomic mass:
It is found that, the actual atomic mass of a
carbon-12 atom is equal to 1.9926 X 10-23g.
Thus by multiplying the relative atomic mass
with 1.6605 × 10-24 g we can get the absolute or actual mass
of an atom.
Example -1 - Find the absolute mass oxygen.
Example – 2 – Find the absolute mass of
Sodium.
Example – 3 – Calculate the absolute mass of
hydrogen atom.
Example – 4 - Calculate the absolute or actual
mass of Nitrogen atom.
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Existence of Atoms
Atoms of most of the
elements exist in the form of molecule or ion, since they are most reactive.
For example, hydrogen, oxygen, chlorine, etc. However, atoms of some
elements, which are non-reactive, exist in free-state in nature. For example
helium, neon, argon, etc.
Usually atoms are
exist in following two forms -
• In the form of
molecules
• In the form of ions
Molecule:-
Molecule is the
smallest particle of a compound.
Atoms exist in free
states in the form of molecule.
Most of the atoms
exist in the form of molecule. Molecules are formed by the combination of two
or more elements.
Example: Molecule of
hydrogen (H2), Molecule of oxygen (O2), Molecule of nitrogen (N2), etc.
• Molecules of
elements
• Molecules of Compounds
Molecules of
elements: When two of more atoms of same element combine to form a
molecule these are called molecules of element.
Example:
Hydrogen molecule
(H2). Hydrogen molecule (H2). Molecule of hydrogen is formed by the
combination of two hydrogen atoms.
Oxygen molecule (O2).
Molecule of oxygen is formed by the combination of two oxygen atoms.
Sulphur molecule (S8).
Molecule of sulphur is formed by the combination of eight sulphur atoms.
Phosphoroud molecule
(P4). Molecule of phosphorous is formed by the combination of four
phosphorous atoms.
Molecules of some
non-reactive elements are formed by single atom. For example – helium, neon,
argon, etc. molecules: Molecules of metals formed as big cluster of atoms.
They are represented by their symbols simply. For example: Iron (Fe), Copper
(Cu), Zinc (Zn), etc. These molecules are known as giant molecules.
Carbon is a non-metal,
but it also exists as giant molecule and represented by its symbol ‘C’.
Atomicity
Monoatomic: When
molecule is formed by single atom only, it is called monoatomic molecule.
Generally noble gas forms monoatomic molecules. For example: Helium (He),
Neon (Ne), Argon (Ar), Kr (Krypton), Xenon (Xe), Randon (Rn).
Diatomic: When
molecule is formed by the cDiatomic: When molecule is formed by the
combination of two atoms of it is called diatomic molecule. For example:
Hydrogen (H2), Oxygen (O2), Nitrogen (N2), Chlorine (Cl2), etc.
Triatomic: When
moleucule is formed by the combination of three atoms it is called triatomic
molecule. For example: molecule of ozone (O3)
Tetra-atomic:- When
molecule is formed by the combination of four atoms it is called tetra-atomic
molecule. For example: Phosphorous molecule (P4)
Polyatomic:- When
molecule is formed by the combination of more than two atoms, it is called
polyatomic molecule. For example: Sulphur molecule (S8)
Molecules of
compounds: When molecule is formed by the combination of two or more
atoms of different elements, it is called the molecule of compound.
Example:Molecule of
water (H2O). Molecule of water is formed by the combination of two hydrogen
and one oxygen atoms.
Ions:
Atoms of several
elements exists in the form of ion. Atoms or molecule with negative or
positive charge over them are called ions.
Cations: Ions
having positive charge over them are called cations.
Anions: Ions
having negative charge over them are called anions.
Monoatomic
ions: Ions formed by one atom are called monoatomic ions.
Polyatomic
ions: Ions formed by two or more atoms are called polyatomic ions.
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