CBSE Class 7 Science Advanced Chemistry Chemistry in Daily Life Very Short Answer Questions Set 02

Very Short Answer Questions

Question 1. Why is magnesium used in fireworks?
Answer:
Magnesium burns with a dazzling white flame, and its reaction with oxygen is highly exothermic.
In simple words: It gives a brilliant white light on burning.

Teacher's Note:
1. Burning in oxygen releases a lot of heat and light.
2. It is also used in alloys such as magnalium.

Question 2. Which non-metal is used for the manufacture of pencil lead?
Answer:
Carbon, in the form of graphite.
In simple words: Pencil lead is graphite, a form of carbon.

Teacher's Note:
1. Diamond is another form of carbon.
2. Graphite is mixed with clay for pencils.

Question 3. Why is duralumin used for the manufacture of automobiles and speedboats?
Answer:
Duralumin is very light in weight but hard and has high tensile strength.
In simple words: It is light and strong.

Teacher's Note:
1. It is 95% aluminium with copper, manganese and magnesium.
2. Light weight saves fuel in vehicles.

Question 4. Which chemical compound is used to reduce the acidity of the soil?
Answer:
Gypsum (calcium sulphate dihydrate, \(\ce{CaSO4.2H2O}\)) is the compound named in this chapter for treating soil.
Note: in farming practice, lime (calcium oxide or calcium hydroxide) is the usual material for neutralizing acidic soil, while gypsum is mainly used to condition alkaline soil.
In simple words: The chapter names gypsum, though lime is the usual soil acidity corrector.

Teacher's Note:
1. Answer gypsum if the exam follows this book.
2. Understand the chemistry: a base is needed to neutralize an acid.

Question 5. Which compound of silicon is used for the preservation of eggs?
Answer:
Sodium silicate (water glass).
In simple words: A coating of sodium silicate keeps eggs fresh.

Teacher's Note:
1. It forms a layer that blocks water and air.
2. Bacteria cannot grow, so eggs last longer.

Question 6. Name the hardest compound and write one of its uses.
Answer:
Silicon carbide. It is used in grinding wheels.
In simple words: Silicon carbide is the hardest compound and makes grinding wheels.

Teacher's Note:
1. Its hardness lets it cut other hard materials.
2. It is a compound of silicon and carbon.

Question 7. Write the formulae of glucose, sugar and starch.
Answer:
Glucose: \(\ce{C6H12O6}\)
Sugar: \(\ce{C12H22O11}\)
Starch: \(\ce{(C6H10O5)_n}\)
In simple words: These three are carbohydrates containing C, H and O.

Teacher's Note:
1. Starch is a polymer, so its formula has n.
2. Sugar is made of two glucose-type units.

Question 8. Give an example of a solution which gives us instant energy.
Answer:
A solution of glucose.
In simple words: Glucose solution gives energy quickly.

Teacher's Note:
1. Glucose is the simplest carbohydrate.
2. It is given in drips to weak patients.

Question 9. Write the composition of stainless steel.
Answer:
Iron 83%, chromium 15%, carbon 1% and nickel 1%.
In simple words: Stainless steel is mostly iron with chromium, carbon and nickel.

Teacher's Note:
1. Chromium prevents rusting.
2. The percentages add up to 100.

Question 10. Name the soap commonly used for scrubbing floors.
Answer:
Scouring soap.
In simple words: Scouring soap has sand and pumice stone added.

Teacher's Note:
1. The fillers give a scrubbing action.
2. It is made from laundry soap.

Question 11. How is concrete made?
Answer:
Concrete is made by mixing cement, gravel and sand in the ratio 1 : 2 : 3 by weight with the required quantity of water.
In simple words: Cement, gravel and sand are mixed with water in the ratio 1 : 2 : 3.

Teacher's Note:
1. Concrete is used for roofs, pillars and beams.
2. Adding steel to it gives RCC.

Question 12. What is emulsification?
Answer:
Emulsification is the removal of oil and grease with dirt by soaps and detergents through the formation of an emulsion.
In simple words: It is the cleaning process in which oil is broken into tiny drops held in water.

Teacher's Note:
1. Soap and detergent act as emulsifiers.
2. They form a film around grease spots.

Question 13. Why is glucose given to patients?
Answer:
Glucose is the simplest carbohydrate. It gives instant energy and also supplies water when it is injected as a solution, especially to dehydrated patients.
In simple words: Glucose gives quick energy and water.

Teacher's Note:
1. Dysentery causes loss of water from the body.
2. Glucose solution can be injected directly into the blood.

Question 14. What is annealing?
Answer:
Annealing is the slow cooling of shaped glass under controlled temperature in a long tunnel-type chamber.
In simple words: Glass is cooled slowly in a chamber so that it does not crack.

Teacher's Note:
1. It is the last step of glass manufacture.
2. Slow cooling relieves stress.

Question 15. State whether true or false: Sodium is a very hard metal.
Answer:
False
Sodium is a very soft metal.
In simple words: Sodium is soft, not hard.

Teacher's Note:
1. Sodium can be cut with a knife.
2. Do not confuse alkali metals with iron.

Question 16. State whether true or false: Non-metals are generally non-malleable and non-ductile.
Answer:
True
Non-metals are generally non-malleable and non-ductile.
In simple words: Non-metals break when hammered.

Teacher's Note:
1. They are brittle in solid form.
2. Graphite is a non-metal that conducts electricity.

Question 17. State whether true or false: Platinum is used as a catalyst.
Answer:
True
Platinum is used as a catalyst for most reactions in the gaseous state.
In simple words: Platinum speeds up many gas reactions.

Teacher's Note:
1. It is the least reactive metal used as a catalyst.
2. A catalyst changes the rate of a reaction.

Question 18. State whether true or false: Graphite is a good conductor of heat.
Answer:
False
Graphite is a good conductor of electricity but a bad conductor of heat.
In simple words: Graphite conducts electricity, not heat.

Teacher's Note:
1. It is used for electrodes.
2. Its heat resistance is another useful property.

Question 19. State whether true or false: Xenon and krypton are used in electric bulbs to slow down the sublimation of tungsten.
Answer:
True
These noble gases slow down the loss of the hot tungsten filament by sublimation.
In simple words: They make the bulb filament last longer.

Teacher's Note:
1. Argon also protects the filament from oxidation.
2. Sublimation means a solid turning to gas directly.