CLASS VI PROJECT TOPICS
I MIDTERM
1. Fibres
a. Metal fibres
b. Mineral fibres
c. Fibre Glass
d. Rayon
e. Polyester
2.SERICULTURE
a. Introduction
b. Life cycle of silk worm
c. Steps in silk production
d. Types of silk
e. Uses
3. Unusual plants
a. Agaricus (Mushroom)
b. Algae
c. Croton
d. Mould
e. Cuscuta(parasitic plant)
4. Food processing
a. Introduction
b. Modern methods of food processing(any
three)
c. Benefits of food processing
d. Drawbacks of food processing
e. Food additives
Fig 1: Filtration
Mixture of Solids and Liquids
Sedimentation and Decantation
Sedimentation is the process of separating an insoluble solid from a liquid in which it
is suspended by allowing it to settle to the bottom of the container. If this also involves
pouring off of the liquid leaving the solid behind, it is called decantation.
Filtration
Filtration is used for separating insoluble solids from a liquid.
When a mixture of chalk and water is poured through a filter paper in a funnel,
chalk particles remains as residue in the filter paper, while the water gets
collected in the beaker below as
Evaporation
filtrate. (see Fig. 1)
Evaporation is used for recovering dissolved solid substances from solutions by
evaporating the solvent. The solute “dissolves out” and is left behind.
Salt/sugar can be recovered from a salt/sugar -water mixture by evaporation.
The water evaporates to leave the solute
behind. , ,
 etc. can also
be recovered from their aqueous solutions by evaporation.
Fig 2: Distillation
Crystallisation
Crystallisation is a sophisticated form of evaporation technique in which crystals of
the solute are encouraged to develop during the process of “dissolving out” from the
solution as the solvent evaporates.
Distillation
Distillation is the process of heating a solution containing soluble solids to form
vapours of the liquid and then cooling the vapours to get the liquid back.
A mixture of common salt and water is taken in a
Steam rises up and comes out into the
distillation flask and heated.
condenser, which is a coaxial tube with
a central tube for vapour to pass through, and and outer tube through which
cold water circulates to form a cold water jacket. Steam condenses in the
central tube and collects in a receiver as distillate. (see Fig. 2)
Fig 3: Sublimation of ammonium chloride.(Source: NCERT,
Science IX, p. 8)
Mixture of Solids
Sublimation
Sublimation is a process in which some solids, on heating, are transformed directly
to vapour without passing through the liquid phase, and vice versa. This technique
can be used to separate a mixture of solids, one of which can undergo sublimation.
The vapours are then cooled separately to get the sublimed solid back. (Fig. 3)
Sublimation
is
used
in
the
separation
of
substances
like, , ,  and.
Extraction
In some cases, one substance in the mixture is soluble in a particular liquid solvent
whereas the other(s) is(are) insoluble in it. The process of dissolving out the soluble
component from a mixture, and subsequently treating the solution to get the solid, is
called extraction.
Magnetic Separation
This method of separation is exemplified by the separation of iron filings.
A mixture with iron filings as one of the components can be separated using a
magnet to attract the iron particles away from the mixture.
Fig 4: Chromatography
Chromatography
Chromatography is an advanced technique of separation in which individual
components of a mixture are separated from each other using the property
of differential migration(different rates of flow). Here, a mobile phase, carrying the
mixture, is passed through a selectively adsorbentstationary phase, which can retain
the components of the mixture to different degrees. (Fig. 4)
Mixture of Liquids
Fractional Distillation
Fig 5: Fractional Distillation
Fractional distillation is the process of separating two or more miscible liquids by a
modified distillation process, in which the distillates are collected as fractions having
different boiling points. The separation of the liquids by this method is based on the
difference in their boiling points. (Fig. 5)
Fractional distillation makes use of a fractionating column or distillation column, a
tube which provides different temperature zones inside it during distillation, the
temperature decreasing from bottom to top. It provides surfaces on which
condensations (of less volatile liquids) and vaporizations (of more volatile liquids) can
occur before the vapours enter the condenser in order to concentrate the more
volatile liquid in the first fractions and the less volatile components in the later
fractions.
Fractional distillation is very effective is separating mixtures of volatile components,
and is widely used in laboratories and industries.
Crude petroleum is separated by the process of fractional distillation into
different fractions like gasoline, lubricating oil, kerosene, diesel etc.
Fig 6: Gravity Separation. (Source: NCERT, Science
IX, p. 20)
Gravity Separation
In gravity separation, a mixture of two immiscible liquids can be separated using
a separating funnel, the working of which is based on the differences in the densities
of the liquids. The heavier liquid which settles below is drained out first from below the
funnel into a beaker, and then the lighter liquid is drained out into another beaker.
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NTSE
CTET
MONDAY, JULY 16, 2012
CBSE - Class 9 - CH2 - Is Matter Around Us Pure
Q1: On the basis of composition, how matter is classified?
Answer:

Pure Subtance

Mixture
Q2(NCERT): What is meant by a pure substance?
Answer: A sample of matter containing only one substance is called a pure
substance. In other words all constituents of the substance are same in their
chemical nature.
Q3: What are the characteristics exhibited by a pure substance?
Answer:
1.
A pure substance contains only one kind of atoms or molecules.
2.
It is perfectly homogenous
3.
It has definite composition which does not vary with time.
4.
It has definite melting point, boiling point, density etc.
Q4: What are different categories of pure substance?
Answer:

Elements

Compounds
Q5: Name two properties of a substance to check its purity?
Answer: A pure substance has a fixed melting point or boiling point at
constant pressure. The purity of a substance can be tested by checking its
melting point or boiling point. If a substance is impure i.e. it contains traces of
another substance, the melting and boiling point of that substance will
change.
Q6: Define mixture.
Answer: If two or more substances (elements or compounds) are mixed
together in any proportion, do not undergo any chemical change but retain
their properties, the resulting substance is called mixture.
Q7: What are the kinds of mixture?
Answer:

Homogenous mixture

Hetrogenous mixture
Q8: What are the characteristics of mixture?
Answer:
1. Variable composition: The constituents of a mixture are present in any
ratio. Example: A mixture of sand and salt can be in a ratio of 1:2 or 1:3 by
weight.
2. Only Physical change: The mixture is a result of physical change. The
constituents of a mixture do not bind each other by chemical bonds. Example:
In air the main constituents, i.e., oxygen, nitrogen and carbon dioxide, do not
bind each other with chemical bonds.
3. No specific properties: The properties of a mixture are the average of the
properties of its constituents. Example: The properties of air are average
common properties of nitrogen and oxygen.
4. Homogeneity: Most of the mixtures are heterogeneous, i.e., their
constituents are not spread evenly throughout. However, some mixtures are
homogeneous i.e. constituents are uniformly spread out. Example: In the
mixture of iron and sulphur, at some places iron is more and at some places
sulphur is more.
5. Separation Methods: In general, the constituents of mixture can be
separated by applying suitable physical methods. E.g. Iron can be separated
from the mixture of iron and sulphur with the help of a magnet.
6. Energy changes: In general, no energy is released or absorbed during the
formation of a mixture. Example: On mixing iron and sulphur, heat energy is
neither absorbed nor evolved.
Q 9: List the points of differences between homogeneous and
heterogeneous mixtures.
Answer:
Homogenous Mixture
1. Constituents have uniform composition
throughout the mixture.
2. Air, blood, saturated sugar, water
solution, alloys are examples of
homogenous mixture.
3. Particles Not visible to unaided eye.
4. All solutions are homogenous mixture.
Heterogeneous Mixture
1. Constituents have non-uniform
composition throughout mixture.
2. Rock, oil and water, Mixture of
Iron filling and Sulphur.
3. Particles may be visible to
unaided eye.
4. All suspensions are
heterogeneous mixture.
Q10: Identity which of the following is homogenous mixture or
heterogeneous one. Also identify the type of constituents in mixture
(e.g. gas in gas, gas in liquid, gas in solid etc.)
a. Air
b. Water and Oil (N2 + O2 )
c. Hydrogen in Palladium
d. Aerated Water (CO2 + H2O)
e. Chalk in water
f. Ethyl Alcohol in Water
g. Alloys e.g. brass
h. Dust (e.g. fine sand) in water
i. Sand + iron fillings
j. Sand + ammonium chloride
h. milk
i. Mercury in amalgamated Zinc
Answer:
Type of
Mixture
1. Gas in gas
2. Gas in liquid
3. Gas in solid
4. Liquid in liquid
5. Liquid in solid
6. Solid in liquid
7. Solid in solid
Homogenous
Mixture
Heterogeneous Mixture
Air
Aerated water
Hydrogen in palladium
Ethyl alcohol + Water Water + Oil, Milk
Mercury in
amalgamated Zinc
Sugar in water
Chalk in water, Dust in water
Sand + Iron Fillings, Sand +
Alloys e.g. brass
ammonium chloride
Q11: What are the constituents of brass?
Answer: Brass is an alloy and is a mixture of Zinc(30%) and Copper (70%).
Q12: Alloys cannot be separated by physical means, though it is
considered mixture, Why?
Answer: Alloys are homogeneous mixtures of metals and cannot be
separated into their components by physical methods. But still, an alloy is
considered as a mixture because it shows the properties of its constituents
and can have variable composition.
Q13: What are elements?
Answer: Elements are substances that cannot be chemically broken down into
simpler substances. So an element is made up of only one kind of atoms. For
example, silver is an element which is made up of only silver atoms. Eiements
are the building blocks of all matter.
Q14: How elements are further classified?
Answer: Metals, Non-metals, metalloids.
Q15: What is a compound? Give an example.
Answer: A Compound is u substance made up of two or more elements
chemically combined in a fixed ratio by weight. They are homogeneous and
exhibit definite physical and chemical properties E.g water is a compound. It is
Q45: What are different ways to separate solid mixtures?
Answers:
1.
2.
3.
4.
Hand Picking
Sieving
Magnetic Separation Method
Sublimation
Sieve
credits:wikipedia
Q46: Describe sieving method.
Answer: When the sizes of the components of a mixture are big enough, they
can be separated with the help of sieve. A sieve is a simple mechanical
device in which a mesh is attached to a frame. When the mixture is placed on
the mesh and is stirred, particles of smaller size pass through the mesh while
the bigger particles of the other component remain above the mesh.
E.g. gram can be separated wheat, sieving of sand at construction site etc.
Q47: Winnowing works on what property?
Answer: Winnowing is based on the property that grains are heavier than
husk and hay.
Q48: What are the reasons for separating the constituents of a mixture?
Answer:
1.
To remove any harmful or undesirable constituent.
2.
To obtain a pure sample of a substance.
3.
To obtain useful constituent from a mixture.
Q49: (a) When it is useful to apply sedimentation and decantation?
(b) Give an example where these methods are used?
(c) Explain the process.
Answer: (a) Sedimentation and Decantation are used to separate coarse
particles of a solid which is insoluble in the liquid. Sedimentation works on the
property that heavy particles settle down due to gravity.
(b) e.g. sand in muddy water can be separated using sedimentation and
decantation technique.
Another example is to remove dust from
rice. When water is added, rice grains being heavy settle down while the dust
remains floating on the water.
(c) The particles of sand particles settle down to the bottom of the beaker. The
settling down of heavier particles is called sedimentation. We can transfer the
clear water in the upper layer (supernatent) carefully to another beaker
without disturbing the solid partciles. This is called decantation.
Separating solid-liquid mixtures
Q 50: What principle is applied in centrifugation? Give examples where
this method is applied to separate mixtures.
Answer: Centrifugation works on the principle that that the denser particles
are forced to the
bottom and the lighter particles stay at the top when spun rapidly.
Examples are:
1.
Separating cream from milk (cream comes as top layer)
2.
Used in diagnostic laboratories for blood and urine tests.
3.
Used in washing machines to squeeze out water from wet
clothes.
4.
Used in preparing lactic cultures to prepare cheese (paneer)
from milk in dairies.
Q51: How crystallization is better than evaporation?
Answer: The process of evaporation gives residue which may contain
impurities. When there is requirement to obtain solid without impurity,
crystallization method is preferred.
In general practice, impure solids are obtained by evaporation and are further
purified by crystallization. e.g. salt obtained from sea is further purified by this
method.
In some cases e.g. sugar crystal cannot be obtained by simple evaporation
technique because sugar gets charred on heating to dryness. In such cases,
crystallization technique is applied.
Q52(NCERT): Name the technique to separate
(i) butter from curd
(ii) salt from sea-water
(iii) camphor from salt
Answer:
(i) butter from curd : centrifugation
(ii) salt from sea-water: evaporation followed by crystallization.
(iii) camphor from salt: sublimation
Q53: What is Chromatography?
Answer: Chromatography is a technique used to separate those solutes of a
mixture which are soluble in the same solvent. It works on the principle of
adsorption. It is used to separate the coloured components (dyes) in black
ink.
Q54: A good method to separate alum (phitkari) from impure samples is
(a) Filtration
(b) Sedimentaion
(c) Crystallization
(d) Sublimation
Answer: (c) Crystallization
Q55: A boy buys common salt from the market which is contaminated
with Ammonium Chloride (NH4Cl) and sand. The procedure he should
adopt to obtain pure NaCl is the following :
(a) to mix the sample in water and evaporate the solution
(b) to mix the sample in water and evaporate the decanted solution
(c) to mix the sample in acetone and evaporate the decanted solution
(d) to heat the sample, then mix in water and evaporate the decanted solution
Answer: (d) to heat the sample, then mix in water and evaporate the decanted
solution
Ammonium chloride sublimes, it can be separated from the mixture of salt and
sand by sublimation method. Sand can be separated from the mixture of sand
and salt by dissolving salt in water and then by filtration. Salt can be
separated through the process of evaporation.
Separating liquid-liquid mixtures
Q56(NCERT): Which separation techniques will you apply for the
separation of the following?(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and
ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer:
(a) Sodium chloride from its solution in water. (Evaporation)
(b) Ammonium chloride from a mixture containing sodium chloride and
ammonium chloride. (Sublimation)
(c) Small pieces of metal in the engine oil of a car.(Filtration)
(d) Different pigments from an extract of flower petals. (Chromatography)
(e) Butter from curd. (Centrifugation)
(f) Oil from water. (Separating Funnel)
(g) Tea leaves from tea. (Filtration)
(h) Iron pins from sand. (Magnetic Separation)
(i) Wheat grains from husk. (Winnowing)
(j) Fine mud particles suspended in water.(Sedimentation →Loading
→Filtration)
(Note: for item 'j' Fine mud particles suspended in water., Refer to diagram
'Water purification system in water works' in NCERT book).
Q57