Question

a volume of 50mL of a standard HCl solution is needed to neutralize 50 mL of 1x10-2 M NaOH. what volume of this HCl solution is needed to neutralize 50 mL of 1x10-2 M Ba(OH)2

Answer 1

First the M of HCl must be determined from the titration with NaOH.
NaOH + HCl ==> NaCl + H2O
Since the molar ratio or the reactants is 1:1, one may use
mL x M = mL x M. Use that to determine M HCl.

Then go to the Ca(OH)2 solution.
2HCl + Ba(OH)2 ==> BaCl2 + 2H2O

Here the ratio of the reactants is not 1:1; therefore, a different approach must be used.
moles Ba(OH)2 = M x L.
Moles HCl = twice that (from the coefficients in the balanced equation).
moles HCl = M x L
You know moles and M, calculat L and convert to mL.