CBSE Class 7 Science Advanced Chemistry Acids, Bases and Salts Very Short Answer Questions Set 03

Very Short Answer Questions

Question 1. State true or false: Lead sulphide is a normal salt.
Answer:
True
In simple words: PbS has no replaceable H or OH, so it is normal.

Teacher's Note:
1. Normal salts come from complete neutralization.
2. Lead sulphide is the salt of hydrosulphuric acid, \(\ce{H2S}\).

Question 2. State true or false: Formula of washing soda is \(\ce{Na2CO3.7H2O}\).
Answer:
False. The formula is \(\ce{Na2CO3.10H2O}\).
In simple words: Washing soda has 10 molecules of water, not 7.

Teacher's Note:
1. Remember 10 for washing soda and 7 for Epsom salt and green vitriol.
2. Many students mix these numbers up.

Question 3. State true or false: Nitre is the common name of sodium nitrate.
Answer:
False. Nitre is potassium nitrate (\(\ce{KNO3}\)).
In simple words: Sodium nitrate is Chile saltpetre.

Teacher's Note:
1. Chile saltpetre is \(\ce{NaNO3}\) and nitre is \(\ce{KNO3}\).
2. Both are used in gunpowder and fertilizers.

Question 4. State true or false: Mercuric nitrate is a deliquescent salt.
Answer:
True
In simple words: Mercuric nitrate absorbs moisture from air and dissolves in it.

Teacher's Note:
1. Deliquescent salts include \(\ce{CaCl2}\), \(\ce{MgCl2}\), \(\ce{ZnCl2}\).
2. They become wet on exposure.

Question 5. State true or false: Chile salt petre is used in the manufacture of nitric acid.
Answer:
True
In simple words: Sodium nitrate is a raw material for nitric acid.

Teacher's Note:
1. It is also used in fertilizers and fireworks.
2. The sibling salt nitre is also used for nitric acid.

Question 6. Hydrochloric acid is a _______ acid. (monobasic/dibasic)
Answer:
monobasic
In simple words: \(\ce{HCl}\) gives only one H+ ion.

Teacher's Note:
1. One H+ per molecule means monobasic.
2. Basicity is not the same as strength.

Question 7. Carbonic acid is a _______ acid. (strong/weak)
Answer:
weak
In simple words: It ionizes partly.

Teacher's Note:
1. Only a few molecules ionize in water.
2. Soda water contains it.

Question 8. Sulphur dioxide on hydrolysis gives _______.
Answer:
sulphurous acid (\(\ce{H2SO3}\))
In simple words: \(\ce{SO2}\) plus water gives a weak acid.

Teacher's Note:
1. \(\ce{SO3}\) gives sulphuric acid instead.
2. \(\ce{SO2 + H2O -> H2SO3}\).

Question 9. Acid turns methyl orange solution _______.
Answer:
pink
In simple words: Methyl orange is pink in acid.

Teacher's Note:
1. It turns yellow in base.
2. It is used in titrations.

Question 10. Ammonium hydroxide is an _______ (acid/alkali)
Answer:
alkali
In simple words: It is a soluble base.

Teacher's Note:
1. Its formula is \(\ce{NH4OH}\).
2. It turns red litmus blue.

Question 11. Sodium sulphate is a _______ salt.
Answer:
normal
In simple words: \(\ce{Na2SO4}\) has no replaceable hydrogen or hydroxyl.

Teacher's Note:
1. Both H of \(\ce{H2SO4}\) are replaced by Na.
2. That is why it is a normal salt.

Question 12. Formula of washing soda is _______.
Answer:
\(\ce{Na2CO3.10H2O}\)
In simple words: It is sodium carbonate decahydrate.

Teacher's Note:
1. Deca means 10.
2. It loses 9 water molecules in air, so it is efflorescent.

Question 13. Nitre is the common name of _______
Answer:
potassium nitrate (\(\ce{KNO3}\))
In simple words: \(\ce{KNO3}\) is called nitre.

Teacher's Note:
1. Sodium nitrate is Chile saltpetre.
2. Nitre is a gunpowder ingredient.

Question 14. Mercuric nitrate is a _______ salt. (deliquescent/efflorescent)
Answer:
deliquescent
In simple words: It takes moisture from air and dissolves.

Teacher's Note:
1. Efflorescent salts lose water instead.
2. Deliquescent salts become wet.

Question 15. Chile salt petre is used in the manufacture of _______ (nitric acid/nitrous acid)
Answer:
nitric acid
In simple words: Sodium nitrate is a source of nitric acid.

Teacher's Note:
1. Nitric acid is also made by other routes.
2. Nitrous acid is not made this way.

Teacher's Note:
1. Link each substance with its main use.
2. Milk of magnesia is \(\ce{Mg(OH)2}\).

Teacher's Note:
1. Colour tells the metal: green iron, blue copper.
2. Check the number of water molecules.

Teacher's Note:
1. Make a small table of colours in acid and in base.
2. Blue is the colour of litmus in a base, not in an acid.