Methane is prepared in the laboratory by heating a mixture of sodium ethanoate with soda lime. The chemical constituent(s) of soda lime is/are

Analysis

The question asks for the chemical composition of soda lime, which is a reagent used in the laboratory preparation of methane (an alkane) through a process called decarboxylation.

Concept Explanation

In organic chemistry, the preparation of methane from sodium ethanoate ($CH_3COONa$) involves heating the salt with soda lime. The reaction is represented by the following equation:

• Soda lime is not a single chemical compound but a mixture.
• Sodium hydroxide ($NaOH$) is the active reagent that provides the hydroxide ion to remove the carboxyl group ($–COONa$) from the sodium ethanoate.
• Calcium hydroxide ($Ca(OH)_2$) is added to the mixture to keep the sodium hydroxide in a solid, granular form and to prevent it from being too deliquescent (absorbing moisture from the air and turning into a liquid). It also helps to moderate the reaction.

Step-by-Step Solution

1. Identify the components: Soda lime is a mixture of two main substances: Sodium hydroxide ($NaOH$) and Calcium hydroxide ($Ca(OH)_2$).
2. Evaluate the options: • Option A lists both $Ca(OH)_2$ and $NaOH$, which matches the definition of soda lime. • Option B ($Na_2CO_3$) is a product of the reaction, not the reagent. • Option C ($NaCl$) is common table salt and is not involved in this reaction. • Option D ($NaOH$) is only one part of the mixture; soda lime specifically refers to the combination of $NaOH$ and $Ca(OH)_2$.

Conclusion

The chemical constituents of soda lime are indeed a mixture of sodium hydroxide and calcium hydroxide.

Exam Tip: Remember that "soda" refers to the sodium hydroxide ($NaOH$) and "lime" refers to the calcium hydroxide ($Ca(OH)_2$). This mnemonic will help you identify the mixture easily in future exams.