ada_t

First of all, I would like to say hello and please excuse my English. I`ll do my best. We (finally) did some experiments in our Chemistry class on Wednesday and my group was the first one to finish them all, so the teacher gave us some extra homework. First experiment: We had to use HCl, NaOH and phenolphthalein. We added HCl and 2-3 drops of phenolphthalein and then we added NaOH. When we added it, a white foam was formed and a gas was emitted. We poured more NaOH and the foam reappeared, but after a very short time it disappeared and the solution turned dark pink (or a combination of red and pink). Why was that foam formed and why did the solution become dark pink? It usually used to have that color when phenolphthalein was added in NaOH or in any other solution containing "OH", so why is it different this time? Second experiment: We had to use CuSO4 and NaOH. We added 1-2 ml of CuSO4 and then 1 ml of NaOH. When we added NaOH a blue, insoluble precipitate was formed. As far as I know, the precipitate is Cu(OH)2, but my question is: why was it formed? Thanks for reading!