Determining the concentration of an unknown acid?

Question

I did a chemlab in the following procedure and need some help with questions.
1)Obtain acid in a 100ml erlenmeyer flask, add 35ml of unknown HCl soluton. 2) Add 2 drops of phenolphthalin indicator. 3) Fill buret with NaOH to end point - obtain 50ml buret and fill with 100m solution of NaOH. 4) Titrate NaOH into HCl solution to end point. Record initial buret volume and final volume.
Solution turned pink when there was only 11.4 ml left in buret.
a)Calculate average volume of base added and # of moles of base added. b)Calculate molar concentration of unknown hydrochloric acid solution c)it says to repeat titration 3 times and then asks why I needed to repeat the titration 3 times d)sodium hydroxide solutions react slowly with air. What effect would this have on the molar concentration of sodium hydroxide? What effect would this have on the calculated value of the concentration of hydrochloric acid? Justify answers
e) how could you use a pH meter to indicate end point of titration?

I am pretty much lost on these questions and would appreiciate some help with any of them

Answer 1

Do the experiment carefully.

Answer 2

use a hallmark like widely used indicator... then evaluate the consequent shade exchange of the acid + indicator to the colour chart, which provides you with its pH point. Use logarithms(-lg) to artwork out the concentration of hydrogen ions in the unknown acid. try wikipedia to comprehend a thank you to apply the logarithms to get the concentration.