Aqueous solutions of ammonia, ethylamine and phenylamine are prepared - AQA - A-Level Chemistry - Question 24 - 2018 - Paper 3

To determine the correct order of the pH values for ammonia, ethylamine, and phenylamine, we need to consider their basicity and the resulting pH of their solutions:

1. Ammonia: Ammonia ($ext{NH}_3$) is a weak base that ionizes in water to form hydroxide ions. It has a relatively higher pH.

2. Ethylamine: Ethylamine ($ext{C}_2 ext{H}_5 ext{NH}_2$) is also a weak base but is stronger than ammonia due to the electron-donating effect of the ethyl group, which helps stabilize the positive charge on ammonium ion formed when it acts as a base.

3. Phenylamine: Phenylamine ($ext{C}_6 ext{H}_5 ext{NH}_2$), on the other hand, is weaker than both ammonia and ethylamine. The phenyl group has a withdrawing effect, which makes it less basic than both ammonia and ethylamine.

Based on this analysis, the correct order for the pH values from highest to lowest is:

• Ammonia > Ethylamine > Phenylamine.

Therefore, the correct choice is (A).