What's the pH when adding .240g NaOH to 50.0 mL of 0.200 M HCl.?

Question

I already converted g NaOH to mmol, but I don't know how to figure out what volume solution it should be in? I need the pH of the new solution that is formed after you dilute the mmol NaOH and add it to the HCl. Please help!!

Answer 1

The trick is to consider volumen of the solution constant.

then you got 50 ml of .2M HCl = 10mmol
.240g of NaOH = 6 mmol
NaOH and HCl cancels each other so i have 4 mmol oh HCl

4 mmol HCl in 50 ml = 0.08 M H+

pH = -log H+ = 1.1

Answer 2

You have to assume that the volume is the same. Notice that the NaOH is a solid. Work out the moles of NaOH, the moles of HCl, find out which one is in excess, subtract, work out the new hydrogen ion concentration, and then take the negative log.