Question

At a certain temperature, the value of pKw = 13.4 and measured pH of solution is 7. The solution is
A. Acidic
B. Basic
C. Neutral
D. Unpredictable

Answer 1

In order to find the pH in the above mentioned condition one may find the change in neutral pH of the environment that in normal conditions is observed to be 7 but it may change with a significant change in temperature.

Complete step by step answer:

Firstly we should see that here we can’t say just by seeing pH below 7 that it must be acidic since there is a significant change in temperature.
Secondly As per the value of pKw we should find a pH for neutral scale that would help us to decide whether it lies in the acidic side or the basic one.
Applying the formula for $Kw = [H^{+}][OH^{-}] = 13.4,$ in neutral case $[H^{+}]=[OH^{-}]$ therefore pH that comes out for the above case is 6.7.
Thus we can conclude that if the pH of the given solution is 7 then it must be basic in nature since it is greater than the neutral pH that is 7.

Hence we can say the correct option is $B$.

Note:
Here one should not consider it as a really simple question and choose acidic be the answer as 6.7 is less than the common neutral pH 7. It should be seen that there is a significant temperature change in the solution that makes neutral pH to drop down from 7 to 6.7 that makes it basic instead of being acidic this basically uses the principal of being having equal concentration of both $[H^{+}]$ and $[OH^{-}]$ at the neutral point.