It is a pure single form of matter. A substance has definite properties and compositions. Example – Iron
2. List the points of differences between homogeneous and heterogeneous mixtures.
Solution:
Homogeneous mixture
Heterogeneous mixture
Particles are uniformly distributed throughout the mixture
All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.
Has a uniform composition
Irregular composition
No apparent boundaries of division
Noticeable boundaries of division.
Exercise-2.2 Page: 18
1. Differentiate between homogenous and heterogeneous mixtures with examples.
Solution:
The following are the differences between heterogeneous and homogenous mixtures.
Heterogeneous mixture
Homogeneous mixture
All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.
Particles are uniformly distributed throughout the mixture
Irregular composition
Has a uniform composition
Noticeable boundaries of division.
No apparent boundaries of division
Example: seawater, blood, etc.
Example: rainwater, vinegar, etc.
2. How are sol, solution and suspension different from each other?
Solution:
Attributes
Sol
Solution
Suspension
Type of Mixture
Heterogeneous
Homogeneous
Heterogeneous
Size of particles
10-7 – 10-5cm
Less than 1nm
More than 100nm
Tyndall effect
Exhibited
Not exhibited
May or may not be exhibited
Appearance
Usually glassy and clear
Unclouded and clear
Cloudy and opaque
Visibility
Visible with an ultra microscope
Not visible
Visible with naked eye
Diffusion
Diffuses very slowly
Diffuses rapidly
Do not diffuse
Stability
Pretty stable
Highly stable
unstable
Settling
Get settled in centrifugation
Do not settle
Settle on their own
Example
Milk, blood, smoke
Salt solution, Sugar solution
Sand in water, dusty air
3. To make a saturated solution, 36g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Solution:
Mass of solute (NaCl) = 36 g
Mass of solvent (H2O) = 100 g
Mass of solution (NaCl + H2O) = 136 g
Concentration = Mass of solute/Mass of solution x 100
Concentration = 36/136 x 100 = 26.47%
Hence, the concentration of the solution is 26.47%
Exercise-2.3 Page: 24
1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?
Solution:
A technique known as simple distillation can be used to separate the mixture of miscible liquids, where the difference in boiling point is more than 25°C, to name a few – kerosene and petrol. The whole concept is established on the volatility property of substances. The following are the various steps in the process of simple distillation:
(a) In a distillation flask, take the mixture.
(b) Treat the mixture with heat while a thermometer is affix.
(c) We observe evaporation of petrol as it has a low boiling point.
(d) As the vapours advance towards the condenser, a dip in the temperature causes condensation of the vapours into liquid which can be accumulated in a flask.
(e) We notice that kerosene tends to remain in the flask in a liquid state due to comparatively higher boiling point.
(f) Consequently, the liquids are separated.
2. Name the techniques used to separate the following:
(a) Butter from curd.
(b) Salt from seawater
(c) Camphor from salt
Solution:
a) A process known as centrifugation is used to separate butter from curd. The process is governed on the principle of density.
b) We can use the simple evaporation technique to separate salt from seawater. Distillation causes water to evaporate leaving solid salt behind, hence the production of salt.
c) Sublimation can be used to separate camphor from salt as during the phase change, camphor does not undergo a liquid phase.
3. What type of mixtures are separated by the technique of crystallization?
Solution:
The technique of crystallization is used to separate solids from a liquid solution. It is linked to precipitation, but in this technique, the precipitate is achieved in a crystal form which exhibits extremely high levels of purity. The principle of crystallization can be applied to purify impure substances.
Exercise-2.4 Page: 24
1. Classify the following as physical or chemical changes:
Cutting of trees
Melting of butter in a pan
Rusting of almirah
Boiling of water to form steam
Passing of electric current through water and water breaking into hydrogen and oxygen gases.
Dissolving common salt in water
Making a fruit salad with raw fruits, and
Burning of paper and wood
Solution:
The following is the classification into physical and chemical change
Physical change
Chemical change
Cutting the trees
Boiling of water to form steam
Melting of butter in a pan
Making a fruit salad with raw fruits
Dissolving common salt in water
Rusting of almirah
Passing of electric current through water, and water breaking into hydrogen and oxygen gases
Burning of paper and wood
2. Try segregating the things around you as pure substances and mixtures.
Solution:
Listed below are the classifications based on pure substances and mixtures:
Pure substance
Mixture
Water
Soil
Salt
Salad
Iron
Air
Diamond
Steel
Exercise Page: 28
1. 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.
Solution:
(a) In water, sodium chloride in its solution can be separated through the process of Evaporation.
(b) The technique of sublimation is apt as Ammonium chloride supports Sublimation.
(c) Tiny chunks of metal pieces in engine oil of car can be manually filtered.
(d) Chromatography can be used for the fine segregation of various pigments from an extract of flower petals.
(e) The technique of centrifugation can be applied to separate butter from curd. It is based on the concept of difference in the density.
(f) To separate oil from water which are two immiscible liquids which vary in their densities, separating funnel can be an effective method.
(g) Tea leaves can be manually separated from tea using simple filtration methods.
(h) Iron pins can be separated from sand either manually or with the use of magnets as the pins exhibit strong magnetic quality which can be a key characteristic hence taken into consideration.
(i) The differentiating property between husk and wheat is that there is a difference in their mass. If treated with a small amount of wind energy, a remarkable variation in the moving distance is noticed. Hence to separate them, the sedimentation/winnowing procedure can be applied.
(j) Due to the property of water, sand or fine mud particles tends to sink in the bottom as it is denser provided they are undisturbed. Through the process of sedimentation/decantation water can be separated from fine mud particles as the technique is established on obtaining clear water by tilting it out.
2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.
Solution:
(a) Into a vessel, add a cup of milk which is the solvent, supply it with heat.
(b) Add tea powder or tea leaves to the boiling milk, which acts as a solute. Continue to heat
(c) The solute i.e., the tea powder remains insoluble in the milk which can be observed while it is still boiling.
(d) At this stage, add some sugar to the boiling solution while stirring
(e) Sugar is a solute but is soluble in the solvent
(f) Continuous stirring causes the sugar to completely dissolve in the tea solution hence reaching saturation.
(g) Once the raw smell of tea leaves is vanished and tea solution is boiled enough, take the solution off the heat, filter or strain it to separate tea powder and the tea solution. The insoluble tea powder remains as a residue while the solute (sugar) and the solvent (essenced milk solution) strain through the filter medium which is collected as the filtrate.
3. Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of a substance dissolved in 100 grams of water to form a saturated solution).
Substance dissolved
Temperature in K
283
293
313
333
353
Solubility
Potassium nitrate
21
32
62
106
167
Sodium chloride
36
36
36
37
37
Potassium chloride
35
35
40
46
54
Ammonium chloride
24
37
41
55
66
(a) What mass of potassium nitrate would be needed to produce a saturated solution of
potassium nitrate in 50 grams of water at 313K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the
solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this
temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
Solution:
(a) Given:
Mass of potassium nitrate required to produce a saturated solution in 100 g of water at 313 K = 62g
To find:
Mass of potassium nitrate required to produce a saturated solution in 50 g of water =?
Required amount = 62 x 50/100 = 31
Hence 31 g of potassium nitrate is required.
(b) The solubility of potassium chloride in water is decreased when a saturated solution of potassium chloride loses heat at 353 K. Consequently, Pragya would observe crystals of potassium chloride which would have surpassed it solubility at low temperatures.
(c) Listed below is the solubility of each salt at 293 K:
Solubility of Potassium nitrate —> 32/100
Solubility of Sodium chloride —> 36/100
Solubility of Potassium chloride —> 35/100
Solubility of Ammonium chloride —> 37/100
It is observed that the ammonium chloride salt has the highest amount of solubility when compared to any other salt at 293 K.
(d) Effect of change of temperature on the solubility of salts:
The table clearly depicts that the solubility of the salt is dependent upon the temperature and increases with an increase in temperature. With this we can infer that when a salt arrives at it saturation point at a specific temperature, there is a propensity to dissolve more salt through an increase in the temperature of the solution.
4. Explain the following giving examples.
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) suspension
Solution:
(a) Saturated solution: It is that state in a solution at a specific temperature when a solvent is no more soluble without an increase in the temperature. Example: Excess carbon leaves off as bubbles from a carbonated water solution saturated with carbon.
(b) Pure substance: A substance is said to be pure when it comprises of only one kind of molecules, atoms or compounds without adulteration with any other substance or any divergence in the structural arrangement. Example: Sulphur, diamonds
(c) Colloid: A colloid is a homogenous non-crystalline substance that comprises of ultramicroscopic particles of a particular substance that would be scattered through another substance. The particles in a colloid cannot be segregated via simple filtration or centrifugation such as suspension and do not settle. Example: Blood, Ink.
(d) Suspension: It is a heterogeneous mixture that comprises of solute particles that are insoluble but are suspended in the medium. These particles that are suspended are not microscopic but visible to bare eyes and are large enough (usually larger than a micrometer) to undergo sedimentation.
5. Classify each of the following as a homogeneous or heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.
Solution:
The following is the classification of the given substances into homogenous and heterogenous mixture.
Homogenous mixture
Heterogenous mixture
Soda water
wood
vinegar
air
Filtered tea
soil
6. How would you confirm that a colourless liquid given to you is pure water?
Solution:
We can confirm if a colourless liquid is pure by setting it to boil. If it boils at 100°C it is said to be pure. But if there is a decrease or increase in the boiling point, we infer that water has added impurities hence not pure.
7. Which of the following materials fall into the category of “pure substance”?
(a)Ice
(b)Milk
(c)Iron
(d)Hydrochloric acid
(e)Calcium oxide
(f)Mercury
(g)Brick
(e)Wood
(f)Air.
Solution:
Following substances from the above-mentioned list are pure substances:
Iron
Ice
Hydrochloric acid
Calcium oxide
Mercury
8. Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Solution:
The following are the solutions from the above-mentioned list of mixture:
Sea water
Air
Soda water
9. Which of the following will show the “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution.
Solution:
Tyndall effect is exhibited by only milk and starch solution from the above-mentioned list of solutions.
10. Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood.
Solution:
Elements
Compounds
Mixture
Sodium
Calcium carbonate
Soil
Silver
Carbon dioxide
Sugar solution
Tin
Methane
Coal
Silicon
Air
Blood
Soap
Additional Questions and Answers
What is meant by a substance?
It is a pure single form of matter. A substance has definite properties and compositions. Example – Iron
What type of mixtures are separated by the technique of crystallization?
The technique of crystallization is used to separate solids from a liquid solution. It is linked to precipitation, but in this technique, the precipitate is achieved in a crystal form which exhibits extremely high levels of purity. The principle of crystallization can be applied to purify impure substances.
How would you confirm that a colourless liquid given to you is pure water?
We can confirm if a colourless liquid is pure by setting it to boil. If it boils at 100°C it is said to be pure. But if there is a decrease or increase in the boiling point, we infer that water has added impurities hence not pure.
Notes and Definitions
Purity
Pure substances
Pure substances are elements or compounds.
They are made up of only one kind of entity.
They cannot be broken down into simpler entities by chemical or physical methods.
They have a fixed composition.
Example: Diamond, carbon dioxide.
Mixtures
Mixtures are formed by just mixing two or more pure substances (components) such that each substance retains its own chemical identity.
Types of mixtures
Types:
1. Homogeneous mixture
A mixture which has a uniform composition throughout is called a homogeneous mixture or solution.
Examples: sugar in water, salt in water.
Heterogeneous mixture
A mixture which contains physically distinct parts and has a non-uniform composition is called a heterogeneous mixture.
Examples: Mixture of salt and iron filings, sand and sugar.
Physical vs Chemical Changes
Physical and chemical changes
A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour or state of the substance change. No new substance is formed.
Example: Melting of ice, boiling water.
A substance is said to undergo a chemical change when a new substance with completely new properties (physical and chemical) is formed.
Example: Burning of wood or paper, souring of milk.
Solutions
Solutions and their properties
A solution is a homogeneous mixture of two or more substances.
Properties:
Its particles are too tiny and have a diameter less than 1 nm.
The particles are not visible to naked eyes.
Particles do not scatter a beam of light passing through it and hence do not show the Tyndall effect.
The solute particles never settle down on keeping undisturbed.
The components of a solution cannot be separated using filtration.
Alloys
Alloys are homogeneous mixtures of metals or a mixture of a metal and another element that cannot be separated into their components by physical methods.
Examples:
Steel, a combination of iron (metal) and carbon (non-metal).
Bronze, a combination of copper (metal) and tin (metal).
Brass, a mixture of copper (metal) and zinc (metal).
Concentration of Solutions
Solubility
Solubility is the property showing the ability of a given substance, which is the solute, to dissolve in a solvent.
It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium.
The resulting solution is called a saturated solution.
Factors Affecting Solubility:
Temperature – Solubility increases with temperature. The situation is different for gases. With the increase in temperature, they became less soluble in each other and in water, but more soluble in organic solvents.
Pressure – For the majority of solid and liquid solutes, pressure does not affect solubility. The solubility of gas is directly proportional to the pressure of this gas.
Types of solutions based on the concentration of the solution
Three types of solutions exist based on the concentration of the solution:
Dilute
Concentrated
saturated solution.
Ways of representing the concentration of a solution
The concentration of a solution can be represented in many ways
(i) Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) × 100
(ii) Mass by volume percentage of a solution = (Mass of solute/ volume of solution)×100
Suspensions
Suspension and its properties
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
The solute particles settle down when a suspension is left undisturbed.
They can be separated from the mixture by filtration.
Colloids
Types of mixtures based on particle size
Classified into:
Solution
Suspension.
Colloidal solution.
Colloidal Solutions
A colloidal solution is a mixture in which the substances are regularly suspended in a fluid.
Classified into: Foam, Emulsion, Sol
Tyndall Effect
Tyndall effect is the scattering of light by particles in a colloid or else particles in a very fine suspension.
e.g.It can be observed when sunlight passes through the canopy of a dense forest.
Dispersed phase
The solute-like component of the dispersed particles in a colloid form the dispersed phase.
Dispersion medium
The component in which the dispersed phase is suspended is known as the dispersing medium.
Aerosol
A colloidal solution with dispersed phase solid/liquid and dispersing medium gas is called Aerosol. e.g. clouds
Foam
A colloidal solution with dispersed phase gas and dispersing medium solid/liquid is called Foam. e.g.Shaving cream.
Sols
A colloidal solution with dispersed phase solid and dispersing medium liquid is called Sol. e.g. Milk of magnesia, mud.
Gels and emulsions
A colloidal solution with dispersed phase liquid and dispersing medium solid is called Gel.
A colloidal solution with dispersed phase liquid and dispersing medium liquid is called Emulsion.
Evaporation
The process of conversion of water into water vapour is known as evaporation.
It can be used to separate the volatile component (solvent) from its non-volatile solute.
Introduction to Separation
Separation of components of a mixture
Heterogeneous mixtures can be separated into their constituents by simple physical methods.
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