Question

Soluble salt like sodium sulphite can be prepared in the laboratory by the process of

• A. titration
• B. synthesis
• C. displacement
• D. decomposition

Answer 1

The correct option is D

decomposition

Part 1 Explanation for the correct option

Corrrect option is D

1. A decomposition reaction occurs when a complex substance is broken down into two or more simpler components.
2. In most cases, sodium sulfite is made in a laboratory by reacting sodium hydroxide $\left(\mathrm{NaOH}\right)$ with gaseous sulphur dioxide ${\mathrm{SO}}_2$. The following is the chemical equation for this decomposition reaction is

${\mathrm{SO}}_2+2\mathrm{NaOH}\to {\mathrm{Na}}_2{\mathrm{SO}}_3+{\mathrm{H}}_2\mathrm{O}$

sulphur dioxide + sodium hydroxide $\to$sodium sulfite + water

2. The depletion of the $\left(\mathrm{NaOH}\right)$ reactant can be monitored by adding a few drops of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ , which results in ${\mathrm{SO}}_2$ gas liberation.

Part 2 Explanation for incorrect options

Option A.

1. A titration is a way to determine the concentration of an unknown solution using a solution of known concentration.
2. The titrant (the known solution) is typically added to a known quantity of the analyte (the unknown solution) from a buret until the reaction is complete.
3. So the option is incorrect.

Option B.

The process of building complex chemical compounds from simpler compounds is known as chemical synthesis. So the option is incorrect.

Option C.

The term "displacement reaction" refers to a reaction in which a portion of one reactant is displaced by another reactant. So the option is incorrect.

Conclusion

Therefore, the decomposition method is used to sodium sulphite in the laboratory.