acid alkali 問題(urgent)

It is easy to note down the answer even without seeing your solution.
1. NaCl solution can change the pH of the alkali. It is trivial that NaCl is considered to be neutral with a pH value of 7 at 25 degree celcius. However, it has volume and this dilution would change the pH of the alkali slightly.
2. KOH: The problem is not KOH. The main reason is that the concentration of KOH is the same as that of NaOH, your original alkali. Hence, same pH solution mixed together would not change the pH of the other solution.

加5cm3 of 0.1M KOH，同再加NaOH冇分別，因兩者都係monobasic，一樣都係0.1M，所以兩者的OH- ions濃度一樣。