Answer:
In this titration, solution P (that contains hydrochloric acid) is added into the conical flask that contains sodium hydroxide drop by drop. The indicator (phenolphthalein) changes color when all the NaOH is completely neutralized.
i) Solution P contains hydrochloric acid. Hydrochloric acid is the chemical that reacts with sodium hydroxide to give salt and water.
This type of reaction is called neutralization.
ii) Under alkaline conditions, phenolphthalein appears pink in color. When the solution becomes neutral or acidic, it is colorless.
So, the color change of the mixture at the end point is from pink to colorless.
iii) same explanation from question i,
HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O (l)
iv) no. of moles = volume (in dm3) x concentration
hence,
no. of moles of NaOH used = 25/1000 x 0.1
= 0.0025 mol
From the equation in (iii), since the mole ratio of HCl : NaOH = 1:1, meaning 1 mole of HCl reacts completely with 1 mole of NaOH.
This also means that the no. of moles of NaOH reacted equals to the no. of moles of HCl needed to react with it, which is 0.0025 mol.
Given the concentration of HCl in solution P is 0.1 mol /dm3. (pls correct me if I misunderstood your comment),
if v is the volume of HCl needed,
0.0025 = 0.1 v
v = 0.025 dm3
also = 25 cm3