Is Matter Around Us Pure
Detailed NCERT Solutions & Analysis
In-Text Questions (Page 15)
Q1. What is meant by a substance?
Answer: A substance is a form of matter that has definite properties and constant chemical composition. It cannot be separated into other kinds of matter by any physical process. Example: Pure gold, water, sugar.
Q2. List the points of differences between homogeneous and heterogeneous mixtures.
| Homogeneous Mixture | Heterogeneous Mixture |
|---|---|
| Particles are uniformly distributed throughout the mixture. | Particles are not uniformly distributed. |
| Has a uniform composition. | Has a non-uniform composition. |
| No visible boundaries of separation. | Visible boundaries of separation between constituents. |
| Examples: Sugar solution, Air, Alloys. | Examples: Sand and salt, Oil and water. |
In-Text Questions (Page 18)
Q1. Differentiate between sol, solution and suspension.
| Property | Sol (Colloid) | Solution | Suspension |
|---|---|---|---|
| Type | Heterogeneous (appears homogeneous) | Homogeneous | Heterogeneous |
| Particle Size | 1 nm - 100 nm (Medium) | Less than 1 nm (Very small) | Greater than 100 nm (Large) |
| Tyndall Effect | Shows Tyndall effect. | Does not show. | Shows (until particles settle). |
| Stability | Stable (particles don't settle). | Stable. | Unstable (particles settle). |
Q2. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Given:
Mass of solute (NaCl) =
36 g
Mass of solvent (Water) = 100 g
Mass of Solution = Mass of Solute + Mass of
Solvent
= 36 g + 100 g = 136 g
Concentration (Mass by Mass %):
= (Mass of Solute / Mass of Solution) x 100
= (36 /
136) x 100
= 26.47%
In-Text Questions (Page 24)
Q1. 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?
We can separate them by the process of Simple Distillation.
- Since the difference in boiling points is more than 25K (or 25°C), simple distillation is sufficient.
- Petrol has a lower boiling point, so it vaporizes first, condenses in the condenser, and is collected. Kerosene remains in the flask.
Q2. Name the technique to separate: (i) Butter from curd, (ii) Salt from sea-water, (iii) Camphor from salt.
(i) Centrifugation (Butter from curd).
(ii) Evaporation (Salt from sea-water).
(iii) Sublimation (Camphor from salt).
Q3. What type of mixtures are separated by the technique of crystallization?
Crystallization is used to separate pure solids from impure samples (homogeneous mixtures). Example: Purification of salt from sea water, separation of alum (phitkari) crystals from impure samples.
Main Textbook Exercises
Q1. Which separation techniques will you apply for the separation of the following?
- (a) Sodium chloride from its solution in water: Evaporation
- (b) Ammonium chloride from sodium 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: Centrifugation / Loading
Q2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
- Take water as a solvent in a vessel and boil it.
- Add tea leaves and sugar as solutes.
- Sugar dissolves in water and is soluble, forming a solution.
- Tea leaves are insoluble in water.
- Add milk and boil again.
- Filter the mixture through a sieve (strainer).
- The tea leaves stay behind on the sieve as residue.
- The tea collected in the cup is the filtrate.
Q3. Pragy tested the solubility of three different substances at different temperatures...
(a) For Potassium Nitrate at 313K: Solubility is 62g/100g water. For 50g water, mass = 62/2 =
31g.
(b) On cooling from 353K to room temp, crystals of Potassium Chloride will form because solubility
decreases with decrease in temperature.
(c) Solubility at 293K: Potassium Nitrate (32g), Sodium Chloride (36g), Potassium Chloride (35g),
Ammonium Chloride (37g). Highest solubility: Ammonium Chloride.
Q4. Explain the following giving examples.
(a) Saturated Solution: A solution in which no more solute can be dissolved at that temperature. Ex: Adding salt to water until it stops dissolving.
(b) Pure Substance: Consists of a single type of particles. Ex: Iron, Water.
(c) Colloid: Heterogeneous mixture where particle size is intermediate between solution and suspension. Ex: Milk.
(d) Suspension: Heterogeneous mixture containing solid particles large enough for sedimentation. Ex: Chalk powder in water.
Is Matter Around Us Pure
Detailed Chapter Analysis & Mixtures
1. Pure Substances vs Mixtures
Matter can be classified into two main types based on its composition.
- Consists of only one type of particles (atoms or molecules).
- Homogeneous in nature.
- Definite chemical composition.
- Fixed melting and boiling points.
- Examples: Iron, Water, 24-carat Gold.
- Consists of two or more pure substances mixed together physically.
- Can be homogenous or heterogeneous.
- Variable composition.
- No fixed melting/boiling points.
- Examples: Air, Soil, Milk, Salt water.
2. Types of Mixtures
A. Homogeneous Mixtures (Solutions)
A mixture which has a uniform composition throughout. The particles are mixed at the molecular level.
- True Solution: A solution involves a solute dissolved in a solvent. Size of particles is less than 1 nm (10^-9 m).
- Examples: Sugar in water, Alloys (Brass).
B. Heterogeneous Mixtures
A mixture which has a non-uniform composition and visible boundaries of separation.
A heterogeneous mixture containing solid particles that are large enough for sedimentation. Particles are visible to naked eye (>100 nm).
Appears homogeneous but is heterogeneous. Particles size is between true solution and suspension (1 nm - 100 nm). Particles scatter a beam of light passing through it (Tyndall Effect).
3. Concentration Formulae
The concentration of a solution is the amount of solute present in a given amount of solution.
= (Mass of Solute / Mass of Solution) x 100
= (Mass of Solute / Volume of Solution) x 100
4. Separation Techniques
Used to separate a volatile component (solvent) from a non-volatile component (solute).
Example: Blue dye from ink.Denser particles are forced to the bottom and lighter particles stay at the top when spun rapidly.
Example: Cream from milk, blood tests.Separates mixtures containing a sublimable volatile component from a non-sublimable impurity.
Example: Ammonium chloride, camphor, naphthalene.Separates solutes that dissolve in the same solvent.
Example: Pigments from natural flowers, drugs from blood.Separates miscible liquids that boil without decomposition and have sufficient difference in boiling points (>25 K).
Example: Acetone and water.Separates miscible liquids with boiling point difference less than 25 K.
Example: Components of air, petroleum fractions.Key Facts & Definitions
50+ Important Points to Remember
Consists of a single type of particles (atoms or molecules).
Consists of more than one kind of pure form of matter.
Mixture with uniform composition throughout (e.g., sugar in water).
Mixture with non-uniform composition and visible boundaries (e.g., sand and salt).
A homogeneous mixture of two or more substances.
Homogeneous mixture of metals or non-metals that cannot be separated by physical means.
An alloy of Zinc (30%) and Copper (70%).
The component of solution dissolved in the solvent (usually lesser quantity).
The component of solution that dissolves the other component (usually larger quantity).
Less than 1 nm (10^-9 m) in diameter.
Solution particles are too small to scatter a beam of light.
Solute particles do not settle down when left undisturbed.
A solution where no more solute can be dissolved at a given temperature.
The amount of solute present in saturated solution at a specific temperature.
Contains less solute than the saturation level.
Heterogeneous mixture with particles large enough to settle down.
Heterogeneous but appears homogeneous; particles scatter light.
Scattering of a beam of light by colloidal particles.
Solute-like component in a colloid.
Component in which the dispersed phase is suspended.
Liquid or solid dispersed in gas (e.g., Fog, Smoke).
Gas dispersed in liquid (e.g., Shaving cream).
Liquid dispersed in liquid (e.g., Milk, Face cream).
Solid dispersed in liquid (e.g., Milk of Magnesia).
Liquid dispersed in solid (e.g., Jelly, Cheese, Butter).
Separates non-volatile solute from volatile solvent.
Denser particles forced to bottom, lighter stay top.
Separates immiscible liquids based on density (Oil and Water).
Separates sublimable volatile component from non-sublimable impurity.
Separates drugs from blood, pigments from natural colors.
Boiling point difference > 25 K.
Boiling point difference < 25 K.
Done by Fractional Distillation of liquid air.
Process that separates a pure solid in the form of its crystals from a solution.
Better than evaporation because some solids decompose or char on heating.
Done by crystallization from impure samples.
Basic form of matter that cannot be broken down (Robert Boyle term).
Lustrous, malleable, ductile, good conductors of heat/electricity.
Non-lustrous, poor conductors, brittle.
Elements having intermediate properties (Boron, Silicon, Germanium).
Substance composed of two or more elements chemically combined in fixed ratio.
Mixture retains properties of constituents; Compound has new properties.
The only metal which is liquid at room temperature.
A non-metal which is liquid.
A non-metal which is lustrous.
Metals melting at temperature slightly above room temperature.
Involves sedimentation, loading, filtration, and chlorination.
(Mass Solute / Mass Solution) * 100.
(Vol Solute / Vol Solution) * 100.
Solution of iodine in alcohol (iodine is solute, alcohol is solvent).