CBSE Class 7 Science Advanced Chemistry Acids, Bases and Salts Very Short Answer Questions Set 01

Very Short Answer Questions

Question 1. The acids which are obtained from the minerals are called __________.
Answer:
mineral acids
In simple words: Acids made from minerals of the earth's crust are mineral acids.

Teacher's Note:
1. Mineral acids are also called inorganic acids.
2. Examples: \(\ce{HCl}\), \(\ce{H2SO4}\) and \(\ce{HNO3}\).

Question 2. The oxides of __________ on hydrolysis give bases.
Answer:
metals
In simple words: A metal oxide that dissolves in water makes a base.

Teacher's Note:
1. Metal oxides are basic and nonmetal oxides are acidic.
2. Example: \(\ce{Na2O}\) + \(\ce{H2O}\) gives \(\ce{NaOH}\).

Question 3. Ammonium hydroxide on heating gives __________ and __________.
Answer:
ammonia and water
In simple words: Heating breaks ammonium hydroxide into ammonia gas and water.

Teacher's Note:
1. The reaction is \(\ce{NH4OH -> NH3 + H2O}\) (on heating).
2. It happens even on slight heating.

Question 4. Zinc on reaction with dilute sulphuric acid liberates __________ gas.
Answer:
hydrogen (\(\ce{Zn + H2SO4 -> ZnSO4 + H2}\))
In simple words: Zinc pushes hydrogen out of the acid and forms zinc sulphate.

Teacher's Note:
1. Active metals displace hydrogen from dilute acids.
2. Bubbles of hydrogen can be tested with a burning splinter.

Question 5. Mineral acids react with metallic carbonate to form its respective metallic salt, __________ and __________.
Answer:
carbon dioxide and water
In simple words: Acid plus carbonate gives salt, water and carbon dioxide gas.

Teacher's Note:
1. Example: \(\ce{CaCO3 + 2HCl -> CaCl2 + H2O + CO2}\).
2. The gas turns lime water milky.

Question 6. Methyl orange turns lime water __________.
Answer:
yellow
In simple words: Lime water is basic, and methyl orange is yellow in a base.

Teacher's Note:
1. Methyl orange: pink in acid, yellow in base.
2. Lime water is a solution of calcium hydroxide.

Question 7. Chemical formula and chemical name of plaster of Paris are __________ and __________ respectively.
Answer:
\( \ce{CaSO4}\cdot\frac{1}{2}\ce{H2O} \) and calcium sulphate hemihydrate
In simple words: Plaster of Paris has half a molecule of water for every calcium sulphate.

Teacher's Note:
1. Hemi means half.
2. It is used for statues and for setting broken bones.

Question 8. The salt formed by removal of water of crystallization from hydrated salt is called __________.
Answer:
anhydrous salt
In simple words: Remove the water and what is left is the anhydrous form.

Teacher's Note:
1. Anhydrous means without water.
2. Example: white \(\ce{CuSO4}\) is the anhydrous form of blue vitriol.

Question 9. Hydrated zinc sulphate is __________ in colour.
Answer:
white
In simple words: Zinc sulphate crystals, \(\ce{ZnSO4}\).7H2O, are white (white vitriol).

Teacher's Note:
1. Salts of zinc, sodium and potassium are colourless or white.
2. Iron and copper salts are coloured.

Question 10. __________ which is a hydrated salt is used as a fungicide in agriculture.
Answer:
Copper sulphate (blue vitriol, \(\ce{CuSO4.5H2O}\))
In simple words: Blue vitriol kills fungi on crops.

Teacher's Note:
1. Blue vitriol is mixed with lime to make Bordeaux mixture.
2. It has 5 water molecules of crystallization.

Teacher's Note:
1. Sort the acids into strong and weak first.
2. One entry can match more than one item.

Teacher's Note:
1. Decide the salt type from the formula.
2. Nitre has more than one use.

Teacher's Note:
1. Efflorescent loses water, deliquescent dissolves, hygroscopic stays solid.
2. Learn one example for each.

Question 14. Name the acid present in
(a) curd   (b) tamarind
Answer:
(a) Lactic acid
(b) Tartaric acid
In simple words: Curd has lactic acid and tamarind has tartaric acid.

Teacher's Note:
1. Learn the source table of organic acids.
2. Tartaric acid is also found in grapes.

Question 15. Name the acid which is produced by the sting of an ant.
Answer:
Formic acid
In simple words: The burning feeling of an ant bite is due to formic acid.

Teacher's Note:
1. Formic acid is also present in the sting of bees and other insects.
2. Applying a mild base such as baking soda soothes the sting.

Question 16. What is meant by an alkali? Give two examples.
Answer:
An alkali is a base that is soluble in water.
Examples: \(\ce{NaOH}\) (sodium hydroxide) and \(\ce{KOH}\) (potassium hydroxide).
In simple words: All alkalies are bases, but only the water-soluble bases are alkalies.

Teacher's Note:
1. Ammonium hydroxide is also an alkali.
2. Every alkali is a base but not every base is an alkali.

Question 17. Give common names of sodium hydroxide and potassium hydroxide.
Answer:
Sodium hydroxide: caustic soda.
Potassium hydroxide: caustic potash.
In simple words: Both are called caustic because they burn the skin.

Teacher's Note:
1. 'Caustic' refers to the burning action on skin.
2. They are used in making soap.

Question 18. Name the substances formed by the dissolution of following oxides in water.
(a) \(\ce{CO2}\)   (b) MgO
Answer:
(a) \(\ce{CO2 + H2O -> H2CO3}\): carbonic acid
(b) \(\ce{MgO + H2O -> Mg(OH)2}\): magnesium hydroxide
In simple words: A nonmetal oxide gives an acid and a metal oxide gives a base.

Teacher's Note:
1. Write the equation to be sure.
2. \(\ce{CO2}\) is acidic and MgO is basic.

Question 19. What is the action of litmus on an acid and a base?
Answer:
Acid turns blue litmus red.
Base turns red litmus blue.
In simple words: Litmus is red in acids and blue in bases.

Teacher's Note:
1. Neutral solutions do not change either colour.
2. Litmus is a natural dye.