[Denu]

We were doing a Chemistry AS Level practical about 3-4 days ago, and the experiment was about acid-base titration. We used phenolphthalein indicator (2g in 10cm3 of water). When we put the indicator in the base, the colour turned violet/purple. After we had started to slowly neutralize the base, and after we found that the colour turned colourless, we went ahead and did the calculations, and then left the lab. For some reason though, I stayed behind to wash the beakers. This is when I noticed that the phenophalein which had turned colourless in the beaker was not colourless when I spilled the contents of the beaker containing the reagents in the sink. My teacher seems ignorant when I ask her why the colour went to the EXACT SAME state when I spilled the contents of the beaker into the sink even though we saw ALL OF IT turn colourless during the experiment. I don't know what happened, and I don't know if this is normal. Does anyone have an idea?

[Borek]

Are you sure there was no base in the sink, after someone emptied their glass earlier?

This is atypical. If the situation was reversed (that is, purple solution getting back colorless) that would be expected for at least two reasons (dilution lowers pH, atmospheric carbon dioxide lowers pH when dissolved).

[SirRoderick]

A base in the sink I should think.

[Denu]

I should of thought about the base in the sink. There was most likely base in the sink, because we performed the experiment multiple times, and each time we washed the beakers in the same sink.