Question

A cloth strip dipped in onion juice is used for testing a liquid ‘X’. The liquid ‘X’ changes its odour. Which type of indicator is onion juice? The liquid ‘X’ turns blue litmus red. List the observations the liquid ‘X’ will show on reacting with the following: (a) Zinc granules (b) Solid sodium carbonate. Write the chemical equations for the reactions involved?

Answer 1

Liquid ‘$\mathrm{X}$’ changes its odour when dipped in onion juice:

• Since in the above question, they have provided the data that the liquid ‘$\mathrm{X}$’ changes its odour when a cloth strip is dipped in onion juice, this means that the change in the odour represents the acidic nature of the substance.
• Also, since the liquid ‘$\mathrm{X}$’ turns blue litmus to red, the liquid can be defined as acid as the acids tend to change the blue colour of litmus to red.

Onion juice as an indicator:

• Here onion juice which is acting as an indicator to change the colour of the liquid ‘$\mathrm{X}$ when dipped in it.
• The given indicator is also known as an olfactory indicator.

The reaction of the liquid ‘$\mathrm{X}$ with Zinc granules:

• We know, that when this acid reacts with metal, it produces salt with the evolution of hydrogen gas.
• Here, the zinc granules which act as a metal react with the acid (liquid ‘$\mathrm{X}$ ) and produce salt and hydrogen gas.
• The general form of the given reaction can be shown as:
  $\mathrm{Acid}\left(\mathrm{X}\right)+\underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}\to \mathrm{Zn}\mathrm{Salt}\left(\mathrm{s}\right)+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

The reaction of the liquid ‘$\mathrm{X}$ with Solid sodium carbonate:

• When the liquid ‘X’ which acts as an acid undergoes a reaction with the solid sodium carbonate it produces sodium salt and water along with the release of carbon dioxide gas.
• The general form of the given reaction can be shown as:
  $\mathrm{Acid}\left(\mathrm{X}\right)+\underset{(\mathrm{Sodium}\mathrm{carbonate})}{\mathrm{N}{\mathrm{a}}_2\mathrm{C}{\mathrm{O}}_3}\left(\mathrm{s}\right)\to \underset{\left(\mathrm{Sodium}\mathrm{salt}\right)}{\mathrm{Na}\mathrm{Salt}}+\underset{\left(\mathrm{water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\left(\mathrm{Carbon}\mathrm{dioxide}\right)}{\mathrm{C}{\mathrm{O}}_2\left(\mathrm{g}\right)}$