Q: The heat required to melt 2 kg of ice at 0 °C (latent heat of fusion of ice = 336000 J/kg) is:

672000 J. Heat Q = mL = 2 \times 336000 = 672000 J.

Question 1

The spreading of the smell of perfume across a room is evidence that particles of matter:

Accepted Answer

are continuously moving. Diffusion of perfume shows particles are in constant random motion and mix with air particles.

Question 2

The random zig-zag motion of tiny particles suspended in a fluid, seen under a microscope, is called:

Accepted Answer

Brownian motion. Brownian motion is the erratic movement of suspended particles caused by collisions with fast-moving fluid particles.

Question 3

Which of the following is a chemical change?

Accepted Answer

Burning of paper. Burning produces new substances (ash, gases) and is a chemical change; the others are physical.

Question 4

Which set contains ONLY chemical changes?

Accepted Answer

Burning of coal, souring of milk, rusting of iron. Burning, souring and rusting all form new substances (chemical changes); the others are physical.

Question 5

The heat energy absorbed by a solid at its melting point to change into a liquid, without any rise in temperature, is called the:

Accepted Answer

latent heat of fusion. Latent heat of fusion is absorbed at constant temperature to convert solid to liquid.

Question 6

Evaporation of sweat cools our body because evaporation:

Accepted Answer

absorbs latent heat from the body. Evaporating sweat takes latent heat of vaporisation from the skin, producing a cooling effect.

Question 7

The heat required to melt 2 kg of ice at 0 °C (latent heat of fusion of ice = 336000 J/kg) is:

Accepted Answer

672000 J. Heat Q = mL = 2 	imes 336000 = 672000 J.

Question 8

A compound differs from a mixture because in a compound the components are:

Accepted Answer

chemically combined in a fixed ratio. A compound has elements chemically bonded in a fixed proportion, with properties different from its constituents.

Question 9

When iron and sulphur are heated together to form iron sulphide, the product:

Accepted Answer

has properties different from both iron and sulphur. Iron sulphide is a compound whose properties differ from those of iron and sulphur (which can no longer be magnetically separated).

Question 10

Two miscible liquids with different boiling points (e.g. water and alcohol) are best separated by:

Accepted Answer

distillation. Distillation vaporises the more volatile liquid, which is then condensed and collected separately.

Question 11

The technique used to separate the different coloured dyes present in ink is:

Accepted Answer

chromatography. Chromatography separates components (dyes) that travel different distances on a medium.

Question 12

A mixture of common salt and camphor is best separated by:

Accepted Answer

sublimation. Camphor sublimes on heating and can be collected, while the salt is left behind.

Question 13

Anything that occupies space and has mass is called:

Accepted Answer

matter. Matter is anything that has mass and occupies space (volume).

Question 14

When a spoon of sugar dissolves in water without overflowing, it shows that:

Accepted Answer

particles of matter have spaces between them. Sugar particles fit into the spaces between water particles, so the level barely changes.

Question 15

Diffusion is fastest in:

Accepted Answer

gases. Gas particles move fastest and are farthest apart, so diffusion is quickest in gases.

Question 16

Solids, liquids and gases differ mainly in the:

Accepted Answer

arrangement and movement of their particles. The three states differ in how closely packed and how freely moving their particles are.

Question 17

A change in which no new substance is formed and which is usually reversible is a:

Accepted Answer

physical change. Physical changes (e.g. melting, dissolving) form no new substance and are often reversible.

Question 18

The rusting of iron is an example of a:

Accepted Answer

chemical change. Rusting forms a new substance (iron oxide), so it is a chemical change.

Question 19

Melting of ice into water is a physical change because:

Accepted Answer

no new substance is formed and it can be reversed by freezing. Ice and water are the same substance in different states; freezing reverses the change.

Question 20

Dissolving common salt in water is considered a physical change because:

Accepted Answer

the salt can be recovered by evaporation. No new substance forms; evaporating the water recovers the original salt, so it is physical.

Matter & Its States — Homi Bhabha Exam Chemistry MCQs with Solutions

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