Question

When I added 1 drop of phenolphthalein to the water in the container and 1 drop of 0.1 M NaOH to the water in the test tube and gently exhaled...

Answer 1

1. Why was a colour changed observed?
2. What kind of reaction was this?
3. How do I write an equation showing what acid was produced starting with the oxidation of carbon?

Answer 2

0.1 M NaOH is a strong basic solution with a pH of 13. When HIn is added to water, the solution is colorless. As you add the NaOH, the solution becomes pink and eventually becomes colorless once again.
The reaction between NaOH and Hln is a neutralization reaction. The complex structure of Hln (C20H14O4) is just abbreviated as H2P.\[H_2P (aq) + 2OH^- \rightarrow P^{2-} (aq) + 2H_2O (l) \]\[P^{2-} (aq) + OH^- (aq) \rightarrow POH^{3-} (aq)\]The first reaction is from colorless to pink. The second is from pink to once again colorless.