Question

What is the correct answer for these question ?

Answer 1

C is correct.

Explanation:

From the wording of your question, I assume that you are adding sulfuric acid to a flask containing sodium hydroxide and a few drops of phenolphthalein.

A, The solution changes from colourless to pink

FALSE. Phenolphthalein is red in basic solution and colourless in acid. Thus, the colour in the flask changes from pink to colourless as you reach the equivalence point.

B. A precipitate is formed

FALSE. The equation for the neutralization reaction is

`"2NaOH(aq) + H"_2"SO"_4"(aq)" → "Na"_2"SO"_4 + 2"H"_2"O(l)"`

Per the solubility rules, the compounds of Group 1 metals are soluble, so `"Na"_2"SO"_4` is not a precipitate.

C. The solution becomes colourless

TRUE. Phenolphthalein is red in basic solution and colourless in acid. Thus, the colour in the flask changes from pink to colourless as you reach the equivalence point.

D. No hydrogen or hydroxide ions are in the solution

FALSE. At the equivalence point, you have neutralized all the `"OH"^"-"` from the `"NaOH"`. You have a solution of `"Na"_2"SO"_4` in water.

The water undergoes autoionization:

`"H"_2"O" ⇌ "H"^"+" + "OH"^"-"`

Thus, there is always some `"H"^"+"` and `"OH"^"-"` present in the solution.