Question

In which of the following cases pH is greater than 7?
(A) $50ml$ of $0.1M$ HCl + $50ml$ of $0.1M$ NaCl
(B) $50ml$ of $0.1M$ ${H_2}S{O_4}$ + $50ml$ of $0.2M$ NaOH
(C) $50ml$ of $0.1M$ $C{H_3}COOH$+ $50ml$ of $0.1M$ KOH
(D) $50ml$ of $0.1M$ $HN{O_3}$+ $50ml$ of $0.1M$ $N{H_3}$

Answer 1

We will show what is given into the question. Then we will look into what type of reactions will follow and then we will see how we will determine the pH. When we will know the pH then we will know that on what condition a solution is basic or acidic. In the end we will choose the correct option.

Complete step-by-step answer: Step1: We have given four options with solution of acid and bases. We are given molarity of that substance and they will react and shift the pH of the solution.
Step2. The reactions happening above is the acid base reaction. It is a neutralization reaction. When acid and base react the ions get exchanged. The hydrogen ion reacts with the hydroxide ion. It creates salt and water. The pH almost shifts to seven.
Step2. But many times when one of them is more acidic or basic and other is less acidic or basic then many of times the solution is not neutral. So as we see in the question the carboxylic acid i:e $C{H_3}COOH$ , and NaOH the carboxylic acid is a weak acid and NaOH is a strong base. When they will react the final solution will be basic.
Weak acid + strong base = basic solution.
Step3. When the solution is acidic than pH will be less than seven and when solution is basic than the pH will be more than seven.

Hence the option (C) is correct.

Note: The nature of the solution can be found out by the litmus test. The blue litmus paper turns into red under acidic solution, and the red litmus paper turn into the blue under basic conditions.