CBSE Class 7 Science Advanced Chemistry Classification of Matter Very Short Answer Questions Set 02

Very Short Answer Questions

Question 1. What is a metalloid? Give two examples.
Answer:
A metalloid is an element that shows some properties of metals and some of nonmetals.
Examples: germanium and arsenic (also antimony, selenium and tellurium).
In simple words: A metalloid lies between a metal and a nonmetal in its properties.

Teacher's Note:
1. The word 'metalloid' means 'metal-like'.
2. Name any two from the five metalloids.

Question 2. What type of metals are found in free state?
Answer:
Noble metals, such as silver, gold and platinum, are found in the free state. Other metals are found in combined form.
In simple words: Only the unreactive noble metals occur free in nature.

Teacher's Note:
1. Gold, silver and platinum do not easily react, hence they remain free.
2. Most metals are found as compounds called ores.

Question 3. Distinguish sublimate from sublime.
Answer:
Sublime: the vapour formed when a solid changes directly into gas on heating.
Sublimate: the solid obtained when this vapour is cooled.
In simple words: The sublime is the vapour; the sublimate is the solid you get back on cooling.

Teacher's Note:
1. Sublime is formed first, sublimate afterwards.
2. Both words are used only in sublimation.

Question 4. What is sublimation?
Answer:
Sublimation is the process in which a solid changes directly into vapour on heating, without passing through the liquid state. Examples: camphor, iodine and ammonium chloride.
In simple words: A solid turning straight into a gas is sublimation.

Teacher's Note:
1. No liquid stage appears in between.
2. Camphor and naphthalene balls vanish slowly through sublimation.

Question 5. What is meant by intermolecular space and intermolecular forces of attraction?
Answer:
Intermolecular space: the empty space between the molecules of a substance.
Intermolecular forces of attraction: the forces that attract neighbouring molecules towards each other.
In simple words: Intermolecular space is the gap between molecules; forces of attraction are the pull between them.

Teacher's Note:
1. Gaps are smallest in solids and largest in gases.
2. Forces are greatest in solids and least in gases.

Question 6. Mention the factors on which the existence of matter in a particular state depends.
Answer:
The state of matter depends on temperature and pressure.
In simple words: Changing temperature and pressure can change a solid into a liquid or gas.

Teacher's Note:
1. Both factors together decide the state.
2. Water is ice, liquid or steam according to temperature.

Teacher's Note:
1. State the change of state for each.
2. Quote the example of water.

Question 8. "All pure substances are homogenous in nature." Justify.
Answer:
A pure substance is made of identical particles (molecules), so its composition and properties are the same throughout.
These particles are uniformly spread, so every pure substance is homogeneous.
In simple words: A pure substance is the same everywhere, so it is homogeneous.

Teacher's Note:
1. Think of pure water: every drop is the same.
2. Tie the answer to 'one kind of particle'.

Question 9. How can the constituents of compounds and a mixture be separated respectively?
Answer:
The constituents of a compound can be separated only by chemical methods.
The constituents of a mixture can be separated by physical methods, such as filtration, sublimation or distillation.
In simple words: Compounds need chemical methods; mixtures need physical methods.

Teacher's Note:
1. Keep the order 'respectively' in mind.
2. Chemical means a reaction takes place.

Question 10. Give two examples for sublimable substances.
Answer:
Camphor and iodine (ammonium chloride and naphthalene also sublime).
In simple words: These solids change into vapour without melting.

Teacher's Note:
1. Mothballs are a common example from daily life.
2. A sublimable solid can be separated from a non-sublimable one.

Question 11. Name any two metals which are poor conductors of electricity.
Answer:
Bismuth and tungsten. These are the metals named as exceptions in the chapter, since most metals conduct electricity well.
In simple words: Most metals conduct electricity, but bismuth and tungsten are listed as poor conductors.

Teacher's Note:
1. This is an exception to the general rule for metals.
2. Do not confuse it with graphite, a nonmetal that conducts.

Question 12. Mention the difference between a filtrate and a residue.
Answer:
Filtrate: the clear liquid that passes through the filter paper and is collected in the beaker.
Residue: the solid that stays behind on the filter paper.
In simple words: The filtrate passes through; the residue stays on the paper.

Teacher's Note:
1. Filtrate flows, residue remains.
2. Both words come up in the filtration experiment.

Question 13. Name two elements which have atomicity more than three.
Answer:
Phosphorus (\(\ce{P4}\), atomicity 4) and sulphur (\(\ce{S8}\), atomicity 8).
In simple words: Phosphorus has 4 atoms in a molecule and sulphur has 8.

Teacher's Note:
1. Atomicity above two means polyatomic.
2. Ozone has atomicity three, which is not more than three.

Question 14. Name two states of matter which are fluid.
Answer:
Liquids and gases.
In simple words: Liquids and gases can flow, so they are fluids.

Teacher's Note:
1. Fluid means able to flow.
2. Solids are rigid and cannot flow.

Question 15. State whether true or false: Intermolecular space is maximum in gases.
Answer:
True
In simple words: Gas molecules are very far apart, so the gaps are largest.

Teacher's Note:
1. Solids have the least space and gases the most.
2. That is why gases can be compressed.

Question 16. State whether true or false: Metals are highly ductile but nonmalleable.
Answer:
False. Metals are highly ductile and malleable.
In simple words: Metals can be drawn into wires and beaten into sheets.

Teacher's Note:
1. Malleable means beaten into sheets, ductile means drawn into wires.
2. Zinc is a known exception.

Question 17. State whether true or false: Evaporation is a surface phenomenon.
Answer:
True
In simple words: Evaporation happens only at the surface of a liquid.

Teacher's Note:
1. Boiling is the bulk phenomenon.
2. That is why a larger surface speeds up evaporation.

Question 18. State whether true or false: A pure substance is homogeneous in nature.
Answer:
True
In simple words: A pure substance has the same composition throughout.

Teacher's Note:
1. Identical molecules throughout means homogeneous.
2. Mixtures may or may not be homogeneous.

Question 19. State whether true or false: Tellurium shows the properties of both metals and nonmetals.
Answer:
True. Tellurium is a metalloid.
In simple words: Tellurium is a metalloid, so it shares properties of both groups.

Teacher's Note:
1. Learn the five metalloids: germanium, arsenic, antimony, selenium, tellurium.
2. Metalloids sit between metals and nonmetals.