Class 9 Science Chapter 2 question answer is matter around us pure

Ncert Solutions for Class 9 Science Chapter 2: is matter around us pure question answers

Textbook	Ncert
Class	Class 9
Subject	Science
Chapter	Chapter 2
Chapter Name	is matter around us pure class 9 ncert solutions
Category	Ncert Solutions
Medium	English

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In Text Questions Page No: 15

Question 1: What is meant by a substance?

Answer 1: A substance is a type of matter that has a fixed composition and distinct properties. It can be an element or a compound.

Question 2: List the points of differences between homogeneous and heterogeneous mixtures.

Answer 2:

Homogeneous mixtures	Heterogeneous mixtures
Homogeneous mixtures have uniform composition.	Heterogeneous mixtures have non uniform composition.
It has no visible boundaries of separation between its constituents.	It has visible boundaries of separation between its constituents.

In Text Questions Page No: 18

Question 1: Differentiate between homogeneous and heterogeneous mixtures with examples.

Answer 1: 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
Examples: Seawater, blood, etc.	Examples: Rainwater, vinegar, etc.

Question 2: How are sol, solution and suspension different from each other?

Answer 2:

Attributes	Sol	Solution	Suspension
Type of mixture	Heterogeneous	Homogeneous	Heterogeneous
Size of particles	10-7 – 10-5 cm	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 ultramicroscope	Not visible	Visible with the 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

Question 3: 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.

Answer 3: Mass of sodium chloride (solute) = 36 g Mass of water (solvent) = 100 g Mass of solution = 36 + 100 = 136 g Therefore, concentration percentage = mass of solute/mass of solution = 26.47 %

In Text Questions Page No: 19

Question 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

Answer 1:

• Cutting of trees: Physical change
• Melting of butter in a pan: Physical change
• Rusting of almirah: Chemical change
• Boiling of water to form steam: Physical change
• Passing of electric current through water, and water breaking down into hydrogen and oxygen gas: Chemical change
• Dissolving common salt in water: Physical change
• Making a fruit salad with raw fruits: Physical change
• Burning of paper and wood: Chemical change

Question 2: Try segregating the things around you as pure substances or mixtures.

Answer 2: Pure substance: Distilled water, diamond; graphite, gold, sulphur.

Mixture: Curd, ice cream, kerosene oil, cooking oil, steel, vulcanised rubber, solder wire (an alloy of lead and tin).

Exercises

Question 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

Answer 1: (a) Evaporation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Separating funnel
(g) Filtration
(h) Magnetic separation
(i) Gravity separation/ Winnowing
(j) Sedimentation and Decantation

Question 2: Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Answer 2:

1. Boil water, which acts as the solvent.
2. Add tea leaves (the solute) to the hot water.
3. The tea leaves are soluble in water, so they dissolve to form a solution of tea.
4. Add sugar as another solute that also dissolves in the hot solvent (water).
5. If any part of the tea leaves is insoluble, it won’t dissolve.
6. Pour the tea through a strainer. The liquid that passes through is the filtrate.
7. The leftover tea leaves in the strainer are the residue.

Question 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 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 313 K?
(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?

Answer 3: (a) Since 62 g of potassium nitrate is dissolved in 100g of water to prepare a saturated solution at 313 K, 31 g of potassium nitrate should be dissolved in 50 g of water to prepare a saturated solution at 313 K.

(b) The amount of potassium chloride that should be dissolved in water to make a saturated solution increases with temperature. Thus, as the solution cools some of the potassium chloride will precipitate out of the solution.

(c) The solubility of the salts at 293 K are:
Potassium nitrate – 32 g
Sodium chloride – 36 g
Potassium chloride – 35 g
Ammonium chloride – 37 g

Ammonium chloride has the highest solubility at 293 K.

(d) The solubility of a salt increases with temperature.

Question 4: Explain the following giving examples.
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension

Answer 4: (a) Saturated solution: A saturated solution is one in which no more solute can dissolve at a given temperature.
Example: If you keep adding sugar to water and it stops dissolving, the solution is saturated.

(b) Pure substance: A pure substance is made up of only one kind of particle and has a fixed composition.
Example: Distilled water or pure gold (Au).

(c) Colloid: A colloid is a mixture where tiny particles of one substance are evenly spread throughout another, and they don’t settle down.
Example: Milk is a colloid of fat in water.

(d) Suspension: A suspension is a mixture in which the particles of a substance are large and settle down if left undisturbed.
Example: Sand in water.

Question 5: Classify each of the following as a homogeneous or
heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.

Answer 5: The following is the classification of the given substances into homogenous and heterogenous mixtures.

Homogenous mixture	Heterogeneous mixture
Soda water	wood
vinegar	soil
Filtered tea
Air

Question 6: How would you confirm that a colourless liquid given to you
is pure water?

Answer 6:  By finding the boiling point of a given colourless liquid. If the liquid boils at 100°C at atmospheric pressure, then it is pure water. This is because pure substances have fixed melting and boiling point.

Question 7: Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air

Answer 7: The pure substances are:

• Ice
• Iron
• Hydrochloric acid
• Calcium oxide
• Mercury

Question 8: Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water

Answer 8: Sea water, air and soda water are solutions.

Question 9: Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution

Answer 9: Milk and starch solution have larger particles since they are not true solutions so they will show tyndall effect.

Question 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

Answer 10: (a) Sodium — Element
(b) Soil — Mixture
(c) Sugar solution — Mixture
(d) Silver — Element
(e) Calcium carbonate — Compound
(f) Tin — Element
(g) Silicon — Element
(h) Coal — Mixture
(i) Air — Mixture
(j) Soap — Mixture
(k) Methane — Compound
(l) Carbon dioxide — Compound
(m) Blood — Mixture

Question 11: Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron fillings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of candle

Answer 11:

1. Plant growth: Five types of hormones are found in plants, which cause plant growth through chemical processes.
2. Rusting of iron: Iron forms undesirable substances when it comes in contact with moisture.
3. Cooking of food: Vapors arise while cooking food which is a chemical change.
4. Digestion of food: There are chemicals inside our body for digestion.
5. Burning of candle: Oxygen is required for this so it is a chemical change.