NCERT QUESTIONS: CHAPTER-2: IS MATTER AROUND US PURE?
NCERT INTEXT QUESTIONS(P-15)
- What is meant by a substance?
A material that is composed of only one type of particles is called a pure substance. All the constituent particles of a pure substance have the same nature. It cannot be separated into other kinds of matter by any physical process.
- List the points of differences between homogeneous and heterogeneous mixtures.
| Homogeneous mixtures | Heterogeneous mixtures | ||
| i. | It has a uniform composition. | i. | It doesn’t have a uniform composition. |
| ii. | It has no visible boundary/boundaries of separation between its constituents. | ii. | It has visible boundary/boundaries of separation between its constituents. |
| iii. | Different constituents present in it exist in single phase.
Examples: Sugar + water = Sugar solution Iodine + alcohol = Iodine tincture Alloy, Air, etc. |
iii. | They consist of more than one phase.
Examples: Oil + Water, Salt + Sulphur, Milk, Chalk powder + water, etc. |
NCERT INTEXT QUESTIONS(P-18)
- Differentiate between homogeneous and heterogeneous mixtures with examples.
Please refer Q2 above for the answer.
- How are sol, solution, and suspension different from each other?
| Property | True solution | Sol(Colloidal solution) | Suspension |
| i. Appearance | Homogeneous and transparent. | Heterogeneous and translucent. | Heterogeneous and opaque. |
| ii. Particle size | < 1 nm (10-9m). | 1 nm-100nm. | >100 nm. |
| iii. Visibility | Particles are not visible even with a powerful microscope. | Particles can be seen with a high-power microscope. | Particles can be seen with naked eyes. |
| iv. Stability | Highly stable. | Pretty stable. | Unstable. |
| v. Diffusion | Diffuse rapidly. | Diffuse slowly. | Do not diffuse. |
| vi. Filterability | Passes through filter paper. | Passes through filter paper. | Can be separated by filter paper. |
| vii. Tyndall effect | Not Exhibited. | Exhibited. | May or mayn’t be exhibited |
| viii. Settling | Do not settle. | Get settled in centrifugation. | Settle on their own. |
| ix. Example | NaCl dissolved in water. | Blood | Mud Water. |
- 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.
Mass of solute (sodium chloride) = 36 g
Mass of solvent (water) = 100 g
Mass of solution = Mass of solute + Mass of solvent = 36 g + 100 g = 136 g
NCERT INTEXT QUESTIONS(P-19)
- 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,
- passing of electric current through water and the water breaking down into hydrogen and oxygen gas,
- dissolving common salt in water,
- making a fruit salad with raw fruits and
- burning of paper and wood.
| Physical change | Chemical change |
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- Try segregating the things around you as pure substances or mixtures.
Pure substances: water, copper wire, bread, salt, sugar, and gold.
Mixtures: steel, plastic, paper, talc, milk, lemon juice, clothes, ink, and air.
NCERT EXERCISES (P-22 to 25)
- 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.
(a) Evaporation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Separating funnel
(g) Filtration
(h) Magnetic separation
(i) Winnowing/ sedimentation
(j) Decantation and filtration
- Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.
First, water is taken as a solvent in a pan. This water is allowed to boil.
ii. Add sugar as a solute in it. Heat it till all the sugar dissolves.
iii. You get a solution of water and sugar.
iv. Sugar is soluble in water completely. www.physicsinduction.com
v. Add half a teaspoon of tea leaves; it is insoluble in water.
vi. Boil the content, add milk, which is also soluble in water, and boil again.
vii. Filter the tea with the help of a strainer; the tea collected in the cup is filtrate, and the tea leaves collected on the strainer are residue. - 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?
Mass of Potassium nitrate (KNO3) to produce a saturated solution in 100 g of water is 62g
⸫ Mass of Potassium nitrate (KNO3) to produce a saturated solution in 50 g of water is 31g
(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 us the solution cools? Explain.
As the solution cools, potassium chloride (KCl) gets crystallized or precipitated. Because at 353K, the solubility of potassium chloride (KCl) is 54 g per 100 g of water. Whereas at room temperature, it is 35 g. So, excess potassium chloride (KCl) dissolved gets precipitated.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
Solubility of each salt at 293K is:
| i. Potassium nitrate (KNO3)-32g | ii. Sodium chloride (NaCl)-36g | iii. Potassium chloride (KCl) -35g | iv. Ammonium chloride (NH4Cl)-37g |
At 293K, ammonium chloride (NH4Cl) has the highest solubility.
(d) What is the effect of a change of temperature on the solubility of a salt?
Solubility increases with temperature.
- Explain the following, giving examples:
(a) Saturated solution: A solution in which no more solute can be dissolved in a given amount of solvent at a given temperature is called a saturated solution. g., Suppose 40 g of a solute is the maximum amount that can be dissolved in 100 g of water at 298 K. Then, (100+40) g of solution so obtained is the saturated solution at 298K.
(b) Pure substance: A pure substance means a single substance (matter) that cannot be separated into other kinds of matter by any physical process. A pure substance has a characteristic melting point and boiling point at a given pressure. e.g., gold, silver.
(c) Colloid: A colloid is a heterogeneous mixture in which the size of solute particles is bigger than that of true solution. These particles cannot be seen with naked eyes; they are stable, e.g., ink, blood.
(d) Suspension: It is a heterogeneous mixture in which the solute particles are big enough to settle down, e.g., chalk-water, paints, etc. - Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air, soil, vinegar, filtered tea.
Homogeneous mixture: soda water, air, vinegar, filtered tea.
Heterogeneous mixture: wood, soil. - How would you confirm that a colourless liquid given to you is pure water?
Every liquid has a characteristic boiling point at 1 atmospheric pressure. If the given colourless liquid boils at 100°C at 1 atmospheric pressure, then it is pure water. If the boiling point is even slightly above 100 °C, then it is contaminated. - 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.
Pure substances are:
(a) Ice – a compound
(c) Iron – an element
(d) Hydrochloric acid – a compound
(e) Calcium oxide – a compound
(f) Mercury – an element
- Identify the solutions among the following mixtures.
(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.
Solutions are: sea water, soda water, and air. - Which of the following will show the “Tyndall effect”?
(a) Salt solution; (b) Milk; (c) Copper sulphate solution; (d) Starch solution.
Milk and starch solution. - 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
Elements – Sodium, Silver, Tin, Silicon Compounds –Calcium carbonate, Methane, Carbon dioxide, Soap Mixtures– Sugar solution, Soil, Coal, Air, Blood - Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle.
Chemical changes are:
(a) Growth of a plant
(b) Rusting of iron
(c) Cooking of food
(d) Digestion of food
(e) Burning of a candle