Question

What happens to the temperature of the solution when acid is neutralised?

Answer 1

I guess you are talking about an acid-base neutralization. These are exothermic, meaning they produce heat. At the beginning, there are many OH- ions from the base and H3O+ ions from the acid present. They vigorously react and produce heat. According to the progress of the reaction, there are fewer and fewer ions present and the reacion finally dies down. That is when your solution is neutralized. No more heat is produced.

But that does not necessarily mean a pH of 7. If you neutralize a weak acid with a strong base, your resulting neutralized saline solution will still be alkaline. An example for this would be the neutralization of a weak fatty acid such as stearine with a strong base like sodium hydroxide. The result of this neutralization is common soap. Soap has an alkaline reaction, as your sore skin and itchy eyes tell you when you wash with it or get it into your face.