CBSE Class 9 Science Advanced Chemistry Matter in Our Surrounding Very Short Answer Questions Set 01

Very Short Answer Type

Question 1. ‘Osmosis is a special kind of diffusion’. Comment.
Answer:
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.
Osmosis is the movement of water (solvent) particles through a semipermeable membrane, from a region where water is more plentiful to a region where it is less plentiful.
Because it is also a movement from higher to lower concentration of the particles (here of water), but only through a membrane, osmosis is a special case of diffusion.
In simple words: Osmosis is diffusion of water through a membrane that lets only some particles pass.

Teacher's Note:
1. Remember the keyword semipermeable membrane for osmosis.
2. Ordinary diffusion needs no membrane.

Question 2. A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.
Answer:
Pure water boils at exactly 100 °C at normal pressure, so water boiling at 102 °C is not pure; it has some substance dissolved in it.
A dissolved impurity lowers the freezing point, so this water will not freeze at 0 °C; it will freeze at a temperature below 0 °C.
In simple words: Impurities raise the boiling point and lower the freezing point of water.

Teacher's Note:
1. A pure substance has sharp fixed melting and boiling points.
2. Salt added to ice or water lowers the freezing point in the same way.

Question 3. Name two processes which provide the best evidence for the motion of particles of matter ?
Answer:
Diffusion (for example the spreading of perfume or of bromine vapour in air) and Brownian motion (the zig-zag motion of pollen grains in water or dust in air) give the best evidence that particles of matter are constantly moving.
In simple words: Diffusion and Brownian motion show that particles keep moving.

Teacher's Note:
1. Brownian motion is seen under a microscope or as dust in a beam of sunlight.
2. Both become faster at higher temperature.

Question 4. Write one common characteristic between solid and liquid ?
Answer:
Both solids and liquids have a definite volume (and a definite mass). Both are also much less compressible than gases.
In simple words: Solids and liquids both have a fixed volume.

Teacher's Note:
1. Only gases change their volume to fill the container.
2. Shape is where solids and liquids differ.

Question 5. At what temperature, do solid ice and liquid water co-exist together.
Answer:
Solid ice and liquid water co-exist at 0 °C (273 K), the melting point of ice, at normal atmospheric pressure.
In simple words: At 0 °C ice and water can stay together.

Teacher's Note:
1. At this temperature, heat given to the mixture melts ice without changing the temperature.
2. Give the answer in both °C and K.

Question 6. Name the temperature at which liquid changes into a gas ?
Answer:
The temperature at which a liquid changes rapidly into gas throughout its bulk is its boiling point (100 °C or 373 K for water at normal pressure).
In simple words: It is the boiling point.

Teacher's Note:
1. Boiling point depends on the pressure.
2. Evaporation, by contrast, occurs below the boiling point.

Question 7. Write the name of two substances which shows sublimation.
Answer:
Camphor and naphthalene (moth balls) show sublimation. Ammonium chloride and iodine are other examples.
In simple words: Camphor and naphthalene turn from solid to vapour directly.

Teacher's Note:
1. Do not choose common salt or sugar; they do not sublime.
2. Dry ice (solid carbon dioxide) also sublimes.

Question 8. Does the evaporation of liquid occur only at a fixed temperature ?
Answer:
No. Evaporation takes place at all temperatures below the boiling point of the liquid, though faster at higher temperatures.
In simple words: Evaporation goes on at every temperature below the boiling point.

Teacher's Note:
1. Only boiling happens at a fixed temperature.
2. Wet clothes dry even in winter.

Question 9. Arrange the following substances in the increasing order of interparticle forces. Water, common salt, nitrogen.
Answer:
Nitrogen is a gas (very weak forces), water is a liquid (moderate forces) and common salt is a solid (strong forces).
Increasing order: nitrogen < water < common salt.
In simple words: Gas has the weakest forces, then liquid, then solid.

Teacher's Note:
1. Decide the state at room temperature first.
2. Force order follows solid > liquid > gas.

Question 10. A certain substance ‘A’ can be compressed to very less extent, but takes up the shape of any container in which it is placed. What will be its physical state ?
Answer:
A substance that is hardly compressible (so has definite volume) but takes the shape of its container is a liquid.
In simple words: Little compression and no fixed shape means a liquid.

Teacher's Note:
1. A solid keeps its own shape.
2. A gas would be easily compressed.

Question 11. The melting point of a substance is just below the room temperature. Predict its physical state.
Answer:
At room temperature the substance is already above its melting point, so it has melted. Its state at room temperature is liquid (assuming its boiling point is above room temperature).
In simple words: Above the melting point the substance is a liquid.

Teacher's Note:
1. Compare room temperature with the melting and boiling points.
2. Mercury and gallium behave this way.

Question 12. How the two temperature scales (Celsius) °C and (Fahrenheit) °F are related with each other.
Answer:
The two scales are related by \( \frac{F - 32}{9} = \frac{C}{5} \), that is F − 32 = \( \frac{9}{5} \) C.
Check: C = 0 gives F = 32, and C = 100 gives F = 212.
In simple words: Fahrenheit reading minus 32 equals nine-fifths of the Celsius reading.

Teacher's Note:
1. Ice point is 0 °C = 32 °F and steam point is 100 °C = 212 °F.
2. Use the check values to avoid mixing up the formula.

Question 13. Name A, B, C, D, E and F in the following diagram showing change in their state :

Answer:
A = fusion (melting), B = evaporation (vaporisation), C = condensation, D = solidification (freezing), E = sublimation, F = frosting (deposition, vapour changing directly into solid).
(In the printed figure both reverse arrows are marked D; the arrow from gas to liquid is condensation, C, and is drawn here as C.)
In simple words: Heating and low pressure move matter from solid to gas; cooling and high pressure move it back.

Teacher's Note:
1. Solid to liquid is fusion and liquid to gas is vaporisation.
2. Gas to solid directly is also called deposition in textbooks.