how many ml of 6M HCl solution are required to bring the pH of 10 ml of a 4M NaOH solution to 2.0
You want to end up with pH = 2 or (H^+) = 0.02M
HCl + NaOH ==> NaCl + H2O
You have 10 mL of 4M NaOH = 40 millimolsl NaOH. You will need 40 mmols HCl to neutralize the NaOH. How many mL of 6M HCl is required for that?
mL x M = mmols
mL x 6 = 40 and mL needed is 16.67 of the 6M stuff.
Now you want to add enough EXTRA of the 6M to move the pH from 7 to 2. Again,
mL x M = mL x M
x*6 = (16.67+x)*0.01
Solve for x = mL of the 6M to add to the neutral solution to change from pH 7 to pH 2. It isn't much--the order of 0.03 mL or so if I didn't goof.