Is Matter Around Us Pure NCERT Solution, study material, CBSE Notes

NCERT Solution: Is Matter Around Us Pure

The ‘sea-water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment

Homogeneous— mixture of salts and water only

Heterogeneous— contains salts, water, mud, decayed plant etc.

While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). What technique can be employed to get back the acetone? Justify your choice.

Acetone can be separated from this mixture by distillation. The boiling points of acetone is much lower than that of water. So, it will evaporate and can be collected after condensation.

What would you observe when

(a) a saturated solution of potassium chloride prepared at 60°C is allowed to cool
to room temperature.
(b) an aqueous sugar solution is heated to dryness.
(c) a mixture of iron filings and sulphur powder is heated strongly.

Ans. (a) Solid potassium chloride will separate out.
(b) Initially the water will evaporate and then sugar will get charred.
(c) Iron sulphide will be formed

Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.

Particle size in a suspension is larger than those in a colloidal solution. Also molecular interaction in a suspension is not strong enough to keep the particles suspended and hence they settle down.

Smoke and fog both are aerosols. In what way are they different?

Both fog and smoke have gas as the dispersion medium. The only difference is that the dispersed phase in fog is liquid and in smoke it is a solid.

Classify the following as physical or chemical properties

(a) The composition of a sample of steel is: 98% iron, 1.5% carbon and 0.5% other elements.
(b) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
(c) Metallic sodium is soft enough to be cut with a knife.
(d) Most metal oxides form alkalis on interacting with water.
Ans. Physical properties – (a) and (c)
Chemical properties – (b) and (d)

The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the desired solution and why?

‘C’ has made the desired solution

Name the process associated with the following

(a) Dry ice is kept at room temperature and at one atmospheric pressure.
Ans. Sublimation
(b) A drop of ink placed on the surface of water contained in a glass spreads throughout
the water.
Ans. Diffusion
(c) A potassium permanganate crystal is in a beaker and water is poured into the beaker
with stirring.
Ans. Dissolution/diffusion
(d) A acetone bottle is left open and the bottle becomes empty.
Ans. Evaporation, diffusion
(e) Milk is churned to separate cream from it.
Ans. Centrifugation
(f) Settling of sand when a mixture of sand and water is left undisturbed for some time.
Ans. Sedimentation
(g) Fine beam of light entering through a small hole in a dark room, illuminates the
particles in its paths.
Ans. Scattering of light (Tyndall effect)