Question

An unknown solution having a $pH$ of $3.5$ was titrated with $0.1M$ $NaOH$. Analysis of the resulting titration curve showed a single equivalence point at $pH$ $7$. Therefore, which of the following could be the unknown solute in the initial solution?

• A. $HF$
• B. $HCl$
• C. $LiOH$
• D. $H_{2}S{O}_4$

Answer 1

The correct option is B $HCl$

Since the unknown solution has a pH of 3.5, it is an acidic solution. Hence, the solution cannot be $LiOH$, which is a base. From the titration experiment, we know that a single equivalence point is observed. Thus, the acidic solution is monoprotic. Hence, we can say that the solution is not $H_{2}S{O}_4$. Now, we also know that the equivalence point is obtained at a pH of 7, which indicates that the unknown acidic solution is strong. Among HF and HCl, HCl is the strong monoprotic acid. Hence, B is the right answer.