CBSE Class 7 Science Advanced Chemistry Acids, Bases and Salts Very Short Answer Questions Set 02

Very Short Answer Questions

Question 1. Name a natural indicator.
Answer:
Red cabbage juice (turmeric is another).
In simple words: Plant colours that change in acids and bases are natural indicators.

Teacher's Note:
1. Turmeric is yellow in acid and red in base.
2. Litmus is also obtained from lichens.

Question 2. Give the formulae of the following salts:
(a) blue vitriol   (b) green vitriol   (c) potash alum
Answer:
(a) \(\ce{CuSO4.5H2O}\)
(b) \(\ce{FeSO4.7H2O}\)
(c) \(\ce{K2SO4.Al2(SO4)3.24H2O}\)
In simple words: Blue is copper, green is iron, and alum has potassium and aluminium.

Teacher's Note:
1. Count the water molecules: 5, 7 and 24.
2. Vitriols are hydrated sulphates.

Question 3. Name the salt used for the manufacture of glass. Give its formula.
Answer:
Sodium carbonate (washing soda), \(\ce{Na2CO3.10H2O}\) (anhydrous form \(\ce{Na2CO3}\)).
In simple words: Washing soda is melted with sand to make glass.

Teacher's Note:
1. Sodium nitrate is also used in glass making.
2. Washing soda is also used in washing clothes.

Question 4. Name the salts used for the following purposes:
(a) Purification of water   (b) Fire extinguisher
Answer:
(a) Potash alum
(b) Sodium bicarbonate (baking soda, \(\ce{NaHCO3}\))
In simple words: Alum clears muddy water and baking soda gives out \(\ce{CO2}\) that puts out fire.

Teacher's Note:
1. Bleaching powder is also used to purify water.
2. Soda-acid extinguishers use baking soda and acid.

Question 5. Name the acid present in
(a) lemon   (b) vinegar
Answer:
(a) Ascorbic acid (citric acid is also present)
(b) Acetic acid
In simple words: Lemon contains vitamin C and vinegar contains acetic acid.

Teacher's Note:
1. Citrus fruits contain citric acid.
2. Vinegar is about 5 percent acetic acid.

Question 6. What are neutral oxides? Give examples.
Answer:
Oxides that are insoluble in water and do not form an acid or a base are called neutral oxides.
Examples: \(\ce{NO}\) and \(\ce{CO}\).
In simple words: Neutral oxides neither turn litmus red nor blue.

Teacher's Note:
1. Do not confuse them with acidic and basic oxides.
2. CO and NO are the two to remember.

Question 7. Name the acid and base from which the following salts are formed:
(a) sodium chloride   (b) potassium sulphate   (c) calcium nitrate
Answer:
(a) hydrochloric acid (HCl) and sodium hydroxide (NaOH)
(b) sulphuric acid (\(\ce{H2SO4}\)) and potassium hydroxide (KOH)
(c) nitric acid (\(\ce{HNO3}\)) and calcium hydroxide (\(\ce{Ca(OH)2}\))
In simple words: The metal part comes from the base and the radical part comes from the acid.

Teacher's Note:
1. Split the salt name into metal and radical.
2. '-ide' from hydracids, '-ate' from '-ic' acids.

Question 8. What are the suffixes of salts formed from the following acids?
(a) carbonic acid   (b) nitrous acid   (c) sulphuric acid   (d) nitric acid
Answer:
(a) -ate (carbonate, bicarbonate)
(b) -ite (nitrite)
(c) -ate (sulphate)
(d) -ate (nitrate)
In simple words: '-ic' acids give '-ate' salts and '-ous' acids give '-ite' salts.

Teacher's Note:
1. Carbonic acid is an '-ic' acid, so its salt ends in '-ate'.
2. Nitrous acid is the only '-ous' acid in the list.

Question 9. Write the chemical formula of hypo.
Answer:
\(\ce{Na2S2O3}\) (sodium thiosulphate)
In simple words: Hypo is the common name of sodium thiosulphate.

Teacher's Note:
1. Hypo removes extra chlorine from bleached cloth.
2. It is called an antichlor.

Question 10. Identify the basic and acidic radicals in sodium nitrate.
Answer:
Basic radical: \(\ce{Na+}\).
Acidic radical: \(\ce{NO3-}\).
In simple words: The positive ion is the basic radical and the negative ion is the acidic radical.

Teacher's Note:
1. Metal ions are the basic radicals.
2. \(\ce{NaNO3}\) is Chile saltpetre.

Question 11. Why is KOH called caustic potash?
Answer:
KOH has a causticising (burning) action on skin, so it is called caustic potash.
In simple words: It burns the skin, and it comes from potash.

Teacher's Note:
1. \(\ce{NaOH}\) is called caustic soda for the same reason.
2. Handle both with gloves.

Question 12. Give two examples of hydrated salts.
Answer:
\(\ce{CuSO4.5H2O}\) (blue vitriol) and \(\ce{FeSO4.7H2O}\) (green vitriol). \(\ce{Na2SO4.10H2O}\) is another.
In simple words: Hydrated salts carry a fixed number of water molecules in their crystals.

Teacher's Note:
1. Write the water molecules after a dot.
2. Washing soda is also hydrated.

Question 13. Define water of crystallization.
Answer:
The fixed number of water molecules that combine with each molecule of a salt in its crystals is called water of crystallization.
In simple words: It is the water that is part of the crystal.

Teacher's Note:
1. The salt loses it on heating.
2. Some salts lose their colour when it is lost.

Question 14. What is the formula of plaster of Paris?
Answer:
\( \ce{CaSO4}\cdot\frac{1}{2}\ce{H2O} \) (calcium sulphate hemihydrate)
In simple words: Plaster of Paris is calcium sulphate with half a water molecule.

Teacher's Note:
1. It is made by gently heating gypsum.
2. It sets hard when mixed with water.

Question 15. State true or false: Hydrochloric acid is a monobasic acid.
Answer:
True
In simple words: \(\ce{HCl}\) gives only one H+ ion per molecule.

Teacher's Note:
1. Basicity is the number of H+ ions given by one molecule of acid.
2. \(\ce{HCl -> H+ + Cl-}\) shows one H+.

Question 16. State true or false: Carbonic acid is a strong acid.
Answer:
False. Carbonic acid is a weak acid.
In simple words: Carbonic acid ionizes only partly, so it is weak.

Teacher's Note:
1. Carbonic acid is dibasic and weak.
2. Strong mineral acids are \(\ce{HCl}\), \(\ce{H2SO4}\) and \(\ce{HNO3}\).

Question 17. State true or false: Sulphur dioxide on hydrolysis gives sulphuric acid.
Answer:
False. It gives sulphurous acid: \(\ce{SO2 + H2O -> H2SO3}\).
In simple words: Sulphuric acid comes from sulphur trioxide, not sulphur dioxide.

Teacher's Note:
1. \(\ce{SO2}\) gives \(\ce{H2SO3}\) and \(\ce{SO3}\) gives \(\ce{H2SO4}\).
2. '-ous' goes with fewer oxygen atoms.

Question 18. State true or false: Acids turn methyl orange solution to pink.
Answer:
True
In simple words: Methyl orange is pink in acid and yellow in base.

Teacher's Note:
1. Pink may also be called orange-red.
2. Remember the colours in a table.

Question 19. State true or false: Ammonium hydroxide is an alkali.
Answer:
True
In simple words: It is a base that dissolves in water.

Teacher's Note:
1. Alkali means water-soluble base.
2. \(\ce{NH4OH}\) is a weak alkali.