Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Chapter 2 – Is Matter Around Us Pure

Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure. Most of the material we come into contact with in our daily lives isn’t pure. For example, the air we breathe is composed of many gases, including carbon dioxide, nitrogen, and oxygen. Tap water frequently has a variety of contaminants and dissolved materials in it. Combinations of several compounds can even be found in foods and materials.

Question 1. What is meant by a pure substance?

Answer: A pure substance is a kind of material made up of only one kind of particle with the same chemical makeup. It can be categorised as a compound or an element.

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

Answer:

Homogeneous mixture	Heterogeneous mixture
Uniform composition throughout	Non-uniform composition throughout
Constituents cannot be separated by simple physical means	Constituents can be separated by simple physical means
E.g., salt in water, sugar in water, copper sulphate in water	E.g., sodium chloride and iron fillings, salt and sulphur, oil and water

Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Exercise 2

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

Answer:

Homogeneous mixture	Heterogeneous mixture
Uniform composition throughout	Non-uniform composition throughout
Constituents cannot be separated by simple physical means	Constituents can be separated by simple physical means
E.g., mixtures of salt in water, sugar in water, copper sulphate in water, iodine in alcohol, alloy, and air	E.g., composition of mixtures of sodium chloride and iron fillings, salt and sulphur, oil and water, chalk powder in water, wheat flour in water, milk and water

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

Answer:

Sol (Colloid)	Solution	Suspension
Heterogeneous mixture	Homogeneous mixture	Heterogeneous mixture
Solute particles cannot be seen with the naked eye	Solute particles cannot be seen with the naked eye	Solute particles can be seen with the naked eye
Spread uniformly throughout	Spread uniformly throughout	Suspended throughout the

the mixture

mixture

Tyndall effect is observed

Tyndall effect is not

observed

Tyndall effect is observed

E.g., milk of magnesia

E.g., salt in water, sugar in water, iodine in alcohol, alloy

E.g., chalk powder and water, wheat flour and water

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: Given the mass of solute (here, sodium chloride) = 36 g Mass of solvent (here, water) = 100 g

Then, the mass of solution = Mass of solute + Mass of solvent

= (36 + 100) g

= 136 g

Therefore, concentration (mass by mass percentage) of the solution

=(Mass of solute/Mass of solvent)x 100%

= (36/136)x 100%

= 26.47%

Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Exercise 3

Question 1. Classify the following as chemical or physical changes:

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

Answer:

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
The 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: The pure substances or mixtures present around us are:

Water, salt, sugar, Saltwater, soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food, etc.

Pure substance	Mixture
Water, salt, sugar	Salt water, soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food

Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Exercise

1. Which separation techniques will you apply for the separation of the following?

Sodium chloride from its solution in water.
Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
Small pieces of metal in the engine oil of a car.
Different pigments from an extract of flower petals.
Butter from curd.
Oil from water.
Tea leaves from tea.
Iron pins from sand.
Wheat grains from husk.
Fine mud particles suspended in water.

Answer:

Sodium chloride from its solution in water: Evaporation
Ammonium chloride from a mixture containing sodium chloride and ammonium chloride: Sublimation
Small pieces of metal in the engine oil of a car: Centrifugation or filtration
Different pigments from an extract of flower petals: Chromatography
Butter from curd: Centrifugation
Oil from water: Using a separating funnel
Tea leaves from tea: Filtration
Iron pins from sand: Magnetic separation
Wheat grains from husk: Winnowing
Fine mud particles suspended in water: Centrifugation

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

Answer:

Step-1: Water is taken as a solvent in a saucepan.

Step-2: This water (solvent) is allowed to boil.

Step-3: Tea leaves and milk are added to the solvent as solutes during heating. They come up with a fix.

Step-4: After that, a strainer is used to filter the solution. The residue from the insoluble portion of the solution stays on the strainer.

Step-5: The filtrate is mixed with sugar, which dissolves in it. The necessary tea is the end product.

You guys can also follow us on the social media

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
Substance Dissolved	Solubility (gm/100grams of water)
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 a change in temperature on the solubility of a salt?

Answer:

Given the solubility of potassium nitrate at 313K = 62g/100g of water
It means, 100 g of water contains potassium nitrate = 62g
Therefore, 50 g of water will contain potassium nitrate

= 62/100 X 50 = 31g

In order to create a saturated solution of potassium nitrate in 50 g of water at 313 K, 31 g of potassium nitrate would be required.

b) When the solubility of potassium chloride decreases, some of the soluble potassium chloride will crystallise at room temperature.

c)The solubilities of different salts at 293K are as follows:

Potassium nitrate has a solubility of 32 g/100g of water at 293 K.
Sodium chloride has a solubility of 36 g/100g of water at 293 K.
Potassium chloride has a solubility of 35 g/100g of water at 293 K.
Ammonium chloride has a solubility of 37 g/100g of water at 293 K..

The solubility of Ammonium chloride is highest at this temperature.

d) When the temperature rises, salt becomes more soluble.

4. Explain the following giving examples:

(a) Saturated solution

(b) Pure substance

(c) ColloidSuspension

Answer: A. solution that has dissolved all of the solutes that it is capable of dissolving is said to be saturated (a). That temperature will not allow for the dissolution of any additional solute.

Assume that at 50°C, 1000 g of a solvent may dissolve up to 200 g of a specific solute. Then, at 50°C, a saturated solution is defined as the result of dissolving 200 g of that solute in 1000 g of that solvent.

(b) Pure substance: A substance that is made up of only one kind of particle, meaning that every single particle that makes up the substance has the same chemical characteristics.

Examples of pure substances are ice, sugar, and salt.

A heterogeneous mixture is called a colloid.
Colloids contain solutes that are too tiny for the human eye to see separately.
The mixture contains an even distribution of the colloidal particles.
Colloids are quite stable because the solute particles do not settle when the mixture is left undisturbed.
Filtration is not a useful technique for separating colloids.
Centrifugation is a technique that can be used to separate colloid constituents.
Colloids exhibit the Tyndall phenomenon.

(d) Suspension

A heterogeneous mixture is a suspension.
For the majority of the medium, the suspended solute particles stay suspended. The particles are visible to the unaided eye.
We see the Tyndall effect in suspension.
Suspensions are unstable because the solute particles settle down when the mixture is left undisturbed.
Filtration is one technique that can be used to separate suspension constituents.
A couple of instances of suspensions are concoctions of water and chalk powder or water and wheat flour.

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

Answer:

Homogeneous mixtures	Heterogeneous mixtures
Soda water, air, vinegar, filtered tea	Wood, soil

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

Answer: Each and every pure liquid has a distinct boiling point. The boiling point of pure water is 100°C at 1 atmospheric pressure. The provided colourless liquid is pure water if it boils at precisely 100°C. The liquid in question is not pure water if it boils at any temperature, even somewhat above or below 100°C. Therefore, we may determine if a given colourless liquid is pure water or not by looking at its boiling point.

Question 7. Which of the following materials fall in the category of a “pure substance”?

Ice
Milk
Iron
Hydrochloric Acid
Calcium oxide
Mercury
Brick
Wood
Air

Answer: The pure substances are:

Ice
Iron
Hydrochloric acid
Calcium oxide
Mercury

Question 8. Identify the solutions among the following mixtures:

Soil
Sea water
Air
Coal
Soda water

Answer: The following mixtures are solutions:

(b) Sea water

(e) Soda water

Question 9. Which of the following will show the “Tyndall effect”?

Salt solution
Milk
Copper sulphate solution
Starch solution

Answer: Among the given examples only milk and starch solutions are colloids which will show the “Tyndall effect”.

Question 10. Classify the following into elements, compounds, and mixtures:

Sodium
Soil
Sugar solution
Silver
Calcium carbonate
Tin
Silicon
Coal
Air
Soap
Methane
Carbon dioxide
Blood

Answer :

Elements	Compounds	Mixtures
(a) Sodium	(e) Calcium carbonate	(b) Soil
(d) Silver	(k) Methane	(c) Sugar solution
(f) Tin	(l) Carbon dioxide	(h) Coal
(g) Silicon		(i) Air
		(j) Soap
		(m) Blood

Question 11. Which of the following are chemical changes?

Growth of a plant
Rusting of iron
Mixing of iron fillings and sand
Cooking of food
Digestion of food
Freezing of water
Burning of candle

Answer:

The following changes are chemical changes:

Chemical changes	Physical changes
(a) Growth of a plant	(c) Mixing of iron fillings and sand
(b) Rusting of iron	(f) Freezing of water
(d) Cooking of food
(e) Digestion of food
(g) Burning of candle

Best NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Matter is anything that occupies space and has mass. It can be classified into different types based on its purity:

Pure Substances: These are materials made up of only one type of particle. Pure substances can be elements or compounds. For example, pure gold is made up of only gold atoms, while pure water is made up of only H₂O molecules.
Mixtures: These are combinations of two or more pure substances. Mixtures can be homogeneous (uniform composition, like air or saltwater) or heterogeneous (distinct, separate components, like salad or sand and iron filings).

In our everyday lives, most of the matter we encounter is not pure. For instance, the air we breathe is a mixture of gases like nitrogen, oxygen, and carbon dioxide. Tap water often contains various dissolved substances and impurities. Even foods and materials can contain a blend of different substances.

So, while pure substances do exist, they are often not what we come across in daily life. Understanding the difference between pure substances and mixtures helps us appreciate the complexity of the materials around us.