Chapter 4.3 – Solution | Chapter Solution Class 9

Publisher	: Oriental Book Company Private Limited
Material	: Madhyamik Physical Science Solution
Subject	: Physical Science
Class	: 9 (Madhyamik)
Chapter Name	: Solution

In-Text Questions

Question 4.3.1

Define solution.

Answer

A solution is a homogeneous mixture of two or more chemically non-reacting substances whose composition can be varied within a certain limit.

Question 4.3.2

How many components are needed to make a solution?

Answer

At least two components are needed to make a solution—solute and solvent.

Question 4.3.3

50 g of common salt is dissolved in 100 mL of water. Which one is solute and which one is solvent of these two components?

Answer

Common salt (NaCl) is the solute, and water is the solvent.

Question 4.3.4

11.0 mL of ethyl alcohol and 9.0 mL of water are mixed to prepare a solution. Which component is solvent?

Answer

Ethyl alcohol is the solvent as it is present in a larger amount.

Question 4.3.5

In soda water, which is the solute?

Answer

Carbon dioxide (CO₂) is the solute.

Question 4.3.6

Milky chalk powder suspension is left undisturbed. What will happen?

Answer

The chalk particles will settle down due to gravity, forming a sediment.

Question 4.3.7

What is the dispersed phase and dispersion medium of starch solution?

Answer

Dispersed phase: Starch particles
Dispersion medium: Water

Question 4.3.8

How can colloidal particles be separated?

Answer

Colloidal particles can be separated by ultrafiltration or centrifugation.

Question 4.3.9

Give examples of Tyndal effect you have experienced.

Answer

A beam of light passing through fog.
Sunlight entering a dark room through a small hole.
Headlights of a car in a dusty atmosphere.

Question 4.3.10

What is electrophoresis?

Answer

Electrophoresis is the process of movement of colloidal particles under the influence of an electric field.

Question 4.3.11

What is an emulsion?

Answer

An emulsion is a colloidal solution in which both the dispersed phase and the dispersion medium are liquids.

Question 4.3.12

In the preparation of emulsion of oil in water, what is the role of soap solution?

Answer

Soap solution acts as an emulsifying agent, stabilizing the emulsion by preventing the oil droplets from coalescing.

Question 4.3.13

What happens when H₂O₂ solution is added to sodium thiosulphate solution?

Answer

Milky colloidal sulphur is liberated according to the reaction:

Na₂S₂O₃ + H₂O₂ → Na₂SO₄ + S + H₂O

Question 4.3.14

Why is little amount of gelatin added during the preparation of ice cream?

Answer

Gelatin is added as an emulsifying agent to stabilize the colloidal mixture and prevent ice crystal formation.

Question 4.3.15

Ionic compounds exist in aqueous solution in what form?

Answer

Ionic compounds exist in aqueous solution in the form of free ions.

Question 4.3.16

The ions and molecules in true solutions enter into the intermolecular voids of the solvent water, why?

Answer

Because of their small size, they fit into the intermolecular spaces of water, forming a homogeneous solution.

Question 4.3.17

The macromolecular colloidal particles cannot enter into the intermolecular space of dispersion medium water?

Answer

Due to their large size, macromolecular colloidal particles cannot fit into the intermolecular spaces of water.

Question 4.3.18

What do you mean by solubility of KNO₃ at 25°C is 40?

Answer

It means that at 25°C, 40 g of KNO₃ dissolves in 100 g of water to form a saturated solution.

Question 4.3.19

Why do bubbles of gas come out quickly when you open the lid of a bottle of cold drinks?

Answer

Due to the sudden decrease in pressure, dissolved CO₂ gas rapidly escapes from the solution.

Question 4.3.20

Solubility of sugar in water is affected by which temperature or pressure?

Answer

Solubility of sugar in water is affected by temperature, not pressure.

Question 4.3.21

Why temperature is mentioned to express the solubility of a substance in a solvent?

Answer

Because solubility varies with temperature, a specific temperature must be mentioned for accurate measurement.

Question 4.3.22

You know the solubility of KNO₃ at 40°C and at 60°C. How can you know its solubility at 50°C (without determining experimentally)?

Answer

By interpolation using a solubility curve.

Question 4.3.23

How can you convert an unsaturated solution to a saturated solution and a super saturated solution to a saturated solution?

Answer

Unsaturated to saturated: By adding more solute.
Supersaturated to saturated: By cooling the solution or adding a seed crystal.

Question 4.3.24

How can you identify a super saturated solution?

Answer

By adding a small crystal of solute; if excess solute crystallizes out, the solution was supersaturated.

Question 4.3.25

Write the formula of hydrated sodium thiosulphate.

Answer

Na₂S₂O₃·5H₂O

Question 4.3.26

Write the formula of a crystal with water of crystallization and one without water of crystallization.

Answer

With water of crystallization: CuSO₄·5H₂O (Blue Vitriol)

Without water of crystallization: NaCl (Common salt)

Question 4.3.28

Mention one example of an industry where seeding process is applied.

Answer

The sugar industry uses seeding for crystal formation.

Question 4.3.29

What do you mean by 5% NaOH solution (W/V)?

Answer

It means 5 g of NaOH is dissolved in 100 mL of solution.

Question 4.3.30

73.00g HCl is dissolved in 1000mL solution. What is the molarity of the solution?

Answer

Molarity (M) = Mass of solute / (Molar mass × Volume in litres)

= 73 / (36.5 × 1)

= 2M

Question 4.3.31

What is the gram per litre concentration of a 0.5(M) NaOH solution?

Hints: $g/L concentration = 0.5 \times 40 = 20 g / L$

Answer

g/L concentration = 0.5 × 40 = 20 g/L

Question 4.3.32

Solubility of which of the following depends on both temperature and pressure and which depends on temperature only.

(i) CO₂

(ii) NaNO₃

Answer

CO₂: Depends on both temperature and pressure.

NaNO₃: Depends only on temperature.

Question 4.3.33

Some crystals of sugar are placed at the bottom of a beaker containing water, after some time it is found that the whole of the water becomes sweet. Why?

Answer

Due to diffusion, sugar molecules move throughout the water, forming a homogeneous solution.

Question 4.3.34

Give example of two non-aqueous solvents?

Answer

Petrol, benzene.

Question 4.3.35

Name a solvent which can dissolve rubber.

Answer

Benzene.

Question 4.3.36

Name two solvents used to prepare paint.

Answer

Turpentine oil, xylene.

Question 4.3.37

Mention harmful effects of alcohols and particularly of methanol.

Answer

Alcohols cause dizziness and liver damage; methanol can cause blindness and neurological damage.

Exercise

Very short answer type questions :

Each question carries 1 mark

Choose the correct answer.

Question 1 (i)

The ratio of the components of a solution is

(a) fixed

(b) may vary

(d) may vary within a limit

Answer

(d) may vary within a limit

Question 1 (ii)

Aerated cold drinks contain CO₂, Sugar, and water, here solution is of

(a) Sugar

(b) CO₂

(d) Sugar and CO₂

Answer

(b) CO₂

Question 1 (iii)

Which one is true solution?

(a) Solution of common salt

(b) Solution of chalk

(d) Butter

Answer

(a) Solution of common salt

Question 1 (iv)

Particle size of a colloid is—

(a) 10⁻⁸ cm

(b) 10⁻⁴ cm

(d) 10⁻⁵ – 10⁻⁷ cm

Answer

(d) 10⁻⁵ – 10⁻⁷ cm

Question 1 (v)

Which will not diffuse?

(a) Suspension

(b) True solution

(d) None

Answer

(a) Suspension

Question 1 (vi)

When liquid is dispersed in solid, the production is called

(a) Gel

(b) Sol

(d) Foam

Answer

(a) Gel

Question 1 (vii)

Which of the following in aqueous solution can enter into intermolecular space of water?

(a) Urea

(b) Protein

(d) Starch

Answer

(a) Urea

Question 1 (viii)

Solubility of which increases with increase of temperature?

(a) O₂

(b) NH₃

(d) SO₂

Answer

Question 1 (ix)

Which of the following solutions is unstable?

(a) Saturated

(b) Unsaturated

(d) Colloidal

Answer

Question 1 (x)

Which of the following solvents used to remove nail polish?

(a) Ethyl alcohol

(b) Methyl alcohol

(d) Terpentine oil

Answer

Select the correct word from the words in the brackets to complete each sentence.

Question 2 (a)

A saturated solution can be converted to an unsaturated solution by ___ (heating/cooling).

Answer

A saturated solution can be converted to an unsaturated solution by heating.

Question 2 (b)

Solubility of a gas in water increases by ___ (increasing/decreasing) pressure.

Answer

Solubility of a gas in water increases by increasing pressure.

Question 2 (c)

Solubility of a gas at constant pressure may be increased by ___ (increasing/decreasing) temperature.

Answer

Solubility of a gas at constant pressure may be increased by decreasing temperature.

Question 2 (d)

Sodium chloride remains in solution as ___ (ions/molecules).

Answer

Sodium chloride remains in solution as ions.

Question 2 (e)

Rate of crystallization from saturated solution may be increased by ___ (seeding/heating).

Answer

The rate of crystallization from a saturated solution may be increased by seeding.

Answer the following :

Question 3 (a)

State the biological importance of dissolved O₂ and CO₂ in water.

Answer

Dissolved oxygen (O₂) is essential for the respiration of aquatic organisms, while dissolved carbon dioxide (CO₂) is necessary for photosynthesis in aquatic plants.

Question 3 (b)

What is the effect of temperature on the solubility of KNO₃ and CaSO₄?

Answer

The solubility of KNO₃ increases with an increase in temperature.
The solubility of CaSO₄ decreases with an increase in temperature.

Question 3 (c)

How can you increase the solubility of a given volume of gas in water?

Answer

The solubility of a gas in water can be increased by:

Increasing pressure
Decreasing temperature

Question 3 (d)

Why the CO₂ gas rapidly bubbles out when the lid of its bottle is opened?

Answer

When the bottle is opened, the pressure inside decreases suddenly, causing the dissolved CO₂ gas to escape as bubbles.

Question 3 (e)

Which solution is more concentrated 10 g/L NaOH or 10 molar NaOH solution?

Answer

10 molar NaOH solution is more concentrated because 1 mole of NaOH = 40 g, so 10 M solution contains 400 g/L, which is much higher than 10 g/L NaOH.

Short answer type questions:

Each question carries 2 marks

Question 1

Atul tested the solubility of four different substances at different temperatures and data are noted in the following table. (Results are given in grams/100 grams of water to form a saturated solution).

Substance dissolved in 100g Water

Substance	Solubility at 283K	Solubility at 303K	Solubility at 323K	Solubility at 343K	Solubility at 363K
Potassium nitrate	283	303	323	343	363
Sodium chloride	21	42	82	102	128
Ammonium chloride	24	46	56	57	57
Potassium chloride	35	45	60	66	74

(a) What mass of potassium nitrate would be needed to prepare a saturated solution of potassium nitrate in 50 grams of water at 323K?

(b) The saturated solution of potassium chloride at 363K is cooled to room temperature. What Atul would observe as the solution cools? Explain.

(d) What is the effect of change of temperature on the solubility of a salt?

Answer

(a) At 323K, 100g of water dissolves 323g of potassium nitrate.

For 50g of water:

Mass of KNO₃ needed = (50 × 323) / 100

= 161.5g

(b) As the solution cools, crystals of potassium chloride will start to form because the solubility of potassium chloride decreases with decreasing temperature. The excess dissolved salt will separate as solid crystals.

Potassium Nitrate = 323g
Sodium Chloride = 82g
Ammonium Chloride = 56g
Potassium Chloride = 60g

Potassium Nitrate (KNO₃) has the highest solubility at 323K.

(d) For most solids, solubility increases with an increase in temperature.

For some salts like CaSO₄, solubility decreases with increasing temperature.

Question 2

Classify each of the following as a homogeneous or heterogeneous mixture:
Soda water, air, filtered tea, vinegar.

Answer

Soda water → Homogeneous
Air → Homogeneous
Filtered tea → Homogeneous
Vinegar → Homogeneous

Question 3

Which of the following will show ‘Tyndall effect’?

(a) Salt solution

(b) Milk

(d) Solution of blue vitriol

Answer

Milk and Starch solution show the Tyndall effect because they are colloidal solutions.

Question 4

What will happen when you add a small crystal of the substance in its supersaturated solution?

Answer

The excess solute will crystallize out immediately, and the solution will return to a saturated state because a supersaturated solution is unstable.

Question 5

What is the molar concentration of a 10% NaOH solution?

Answer

Mass of NaOH = 10g

Volume of solution = 100mL = 0.1 L

Molar mass of NaOH = 40 g/mol

Molarity (M) = (Mass of solute in g) / (Molar mass × Volume in L)

= 10 / (40 × 0.1)

= 2.5M

Long answer type questions:

Each question carries 5 marks

Question 1

What are the components to prepare a solution? Compare the particle sizes of suspension, colloids and true solution. How will you identify whether a solution is a true solution?

Answer

A solution consists of two components:

(i) Solute: The substance that dissolves (e.g., salt in water).

(ii) Solvent: The substance in which the solute dissolves (e.g., water).

Type of Mixture	Particle Size	Example
True Solution	Less than 10⁻⁸ cm	Salt solution
Colloid	10⁻⁵ cm – 10⁻⁷ cm	Milk, starch
Suspension	Greater than 10⁻⁴ cm	Muddy water

A true solution does not scatter light, whereas a colloid shows the Tyndall effect.

Question 2

Give common names and examples of the following colloids:

(a) Gas in liquid

(b) Liquid in gas

(d) Liquid in solid

Answer

State of Colloid	Common Name	Examples
Gas in Liquid	Foam	Shaving cream
Liquid in Gas	Aerosol	Perfume spray
Solid in Liquid	Sol	Paint, Muddy water
Liquid in Solid	Gel	Cheese, Jelly

Question 3

What is an emulsion? Classify the emulsions and give examples of each type.

Answer

An emulsion is a colloidal solution where liquid droplets are dispersed in another liquid.

Types of Emulsions:

Oil-in-water (O/W) type: Oil is dispersed in water. (e.g., Milk, Ice cream)
Water-in-oil (W/O) type: Water is dispersed in oil. (e.g., Butter, Cold cream)

Question 4

What is an emulsifier? Mention the use of an emulsifier.

Answer

An emulsifier is a substance that stabilizes an emulsion by preventing the dispersed phase from separating.

Examples:

Soap in oil-water emulsion
Lecithin in food products
Gum Arabic in inks

Question 5

Give examples of micromolecular and macromolecular substances. How do they remain in solution?

Answer

Micromolecular substances (e.g., Glucose, NaCl) form true solutions.
Macromolecular substances (e.g., Proteins, Starch) form colloidal solutions.

Question 6

Define saturated and supersaturated solution.

Answer

Saturated Solution: A solution that contains the maximum solute that can be dissolved at a given temperature.

Supersaturated Solution: A solution that contains more solute than normally possible at a given temperature. It is unstable.

Question 7

How will you distinguish between unsaturated and saturated solution?

Answer

Unsaturated solution – More solute can be dissolved.

Saturated solution – No more solute can be dissolved.

Question 8

What are the factors affecting the solubility of a substance? What is the utility of the solubility curve?

Answer

Factors Affecting Solubility:

Temperature (increases/decreases solubility)
Pressure (affects gas solubility)
Nature of solute & solvent

Solubility Curve helps to predict the solubility at different temperatures.

Question 9

Mention three uses of non-aqueous solvents.

Answer

The three uses of non-aqueous solvents are:-

Alcohol in medicines and perfumes
Petrol as a fuel
Acetone as a nail polish remover

Question 10

Name the industries where the following solvents are used:

(i) Alcohol

(ii) Petrol

(iii) Terpentine oil

(iv) Benzene

(v) Acetone

Answer

Solvent	Industry Used
Alcohol	Pharmaceutical industry
Petrol	Automotive industry
Turpentine oil	Paint industry
Benzene	Chemical industry
Acetone	Cosmetics industry