How many milliliters of 0.135 M HCl are needed to completely neutralize 56.0 mL of 0.101 M Ba(OH)2 solution?

Answer 1

You need an equation.
Ba(OH)2 + 2HCl --> BaCl2 + 2H2O
Think moles.'
moles Ba(OH)2 = M x L = ??

Using the coefficients in the balanced equation, convert moles Ba(OH)2 to moles HCl.
??moles Ba(OH)2 x (2 moles HCl/1 mole Ba(OH)2) = xx moles HCl

Tben the definition of molarity is
M = moles/L.
You have moles HCl and M HCl, solve for L HCl and convert to mL.