Question

On bringing a lighted matchstick near the mouth of the test tube in which $\mathrm{NaOH}\mathrm{and}\mathrm{Zn}$ react:

• A. the matchstick gets extinguished
• B. the matchstick burns faster
• C. a pop sound is heard
• D. no effect is observed on the matchstick

Answer 1

The correct option is C

a pop sound is heard

The explanation for the correct option:

Option C is the correct option.

1. When one mole of zinc reacts with two moles of Sodium hydroxide $\left(NaOH\right)$ it fives Sodium zincate $\left(N{a}_{2}Zn{O}_2\right)$, with Hydrogen $\left(H_2\right)$ gas.
2. The reaction of Zinc with Sodium hydroxide gives Sodium zincate and hydrogen gas is evolved.

$\underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Sodium}\mathrm{hydroxide}\right)}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{Sodium}\mathrm{zincate}\right)}{{\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

3. The hydrogen gas starts released from the vessel.

4. Therefore, if we bring a lighted matchstick near the vessel it burns with a pop sound.

5. It burns with a pop sound because hydrogen has the characteristics property to burn with a pop sound.

Explanation of incorrect options:

Option A:

1. The matchstick does not get extinguished because the ignition temperature of the matchstick is near about $230°C$ and the room temperature is less than the ignition temperature.

Option B:

1. Only the head of the matchstick burns faster because this head is made of Potassium chlorate $\left(KCl{O}_3\right)$ and it releases a lot of Oxygen when it burns.
2. And due to this, the head burns faster but the rest of the body burns slowly.

Option D:

1. A pop sound and the blue flame are observed on the matchstick because of burning the Hydrogen gas.

Final Answer: When Zinc reacts with Sodium hydroxide, a pop sound is heard.