Viva Voce: Properties of Acids & Bases | Lab Manuals for Class 10 PDF Download

Q.1.Explain, why hydrogen gas is not collected by the downward displacement of air?

Hydrogen gas is not collected by the downward displacement of air because hydrogen gas is lighter than air.

Q.2. Which gas is produced when zinc metal reacts with hydrochloric acid?

When zinc metal reacts with hydrochloric acid, hydrogen gas is produced.
Zn(s)+ 2HCl(aq) → ZnCl₂(aq)+ H₂(g)

Q.3. Hydrogen gas is neutral to litmus paper. Explain how?

Hydrogen gas is neither acidic nor basic in nature, thus it does not affect blue and red litmus paper.

Q.4. How can the deposits of carbonates and hydrogen carbonates on the metal surface be cleaned?

The deposits of carbonates and hydrogen carbonates on the metal surface can be cleaned by dil. HCl or acetic acid.

Q.5. When a white powder was mixed with dilute acid, a colourless and odourless gas was produced which turned lime water milky. What is this white powder?

White powder may be carbonate or bicarbonate of metals, which evolve CO₂ on reacting with dilute acid. CO₂ gas turned lime water milky

Q.6. If a moist blue litmus paper is brought near CO₂ gas. What change would be observed on the blue litmus paper?

Blue litmus paper turns red. In the presence of moisture, CO₂ changes to carbonic acid.
CO₂ + H₂O → H₂CO₂
It will change the colour of blue litmus to red.

Q.7. Which substance will be required to identify the gas evolved when dil. HCl reacts with solid sodium carbonate?

Lime water will be required. CO₂ is evolved in the reaction which turns lime water milky.

Q.8. Out of acetic acid and hydrochloric acid, which would have a lower pH?

HCI would have lower pH as it can easily dissociate to give more H⁺ ions as compare to acetic acid.

Q.9. A drop of red litmus solution is poured in a metal carbonate solution. The colour of litmus solution change to blue. What is the nature of metallic carbonate solution?

The metallic carbonate solution is alkaline in nature.

Q.10. Why do metal displace hydrogen from dilute acids?

It is because metals are more reactive than hydrogen, therefore they can displace H₂. They can supply electrons to convert H⁺ ions to H₂ gas.
2H⁺ + 2e^– → H₂(g)

Q.11. Why does lime water turn milky when CO₂ is passed through it?

It is due to the formation of insoluble calcium carbonate.

Q.12. Name one metal (other than zinc) which on reacting with dil. HCl gives a colourless gas that burns with a pop sound.

Magnesium metal evolves hydrogen gas on reacting with dil. HCl. The gas burns with a pop sound.

Q.13. What is the utility of the reaction between NaHCO₃ and HCl in daily life situation?

Sodium bicarbonate (NaHCO₃) acts as an antacid and it neutralises excess of hydrochloric acid (HCl) in our stomach.

Q.14. Which gas is liberated when sodium carbonate reacts with hydrochloric acid?

When sodium carbonate (Na₂CO₃) reacts with hydrochloric acid, carbon dioxide (CO₂) gas is released.
Na₂CO₃(s)+ 2HCl(aq) → 2NaCl(aq)+ CO₂(g)+ H₂O(l)

Q.15. What will happen to a lighted candle if it is brought near the mouth of a gas jar containing hydrogen gas?

The candle extinguishes with a pop sound and the gas burns with a pale blue flame.

Q.16. What will be the colour of a blue litmus paper on bringing it in contact with a drop of dil. hydrochloric acid?

The colour of the blue litmus paper changes to red on bringing it in contact with a drop of dil. hydrochloric acid.