Question

A 25.0 mL solution of HCl is neutralized with 20.5 mL of 0.240 M Ba(OH)₂. What is the concentration of the original HCl solution

Answer 1

2HCl + Ba(OH)2 ==> BaCl2 + 2H2O ... balanced equation

It takes TWO moles HCl for each ONE mole of Ba(OH)2.

Let's find moles Ba(OH)2 present: 12.7 ml x 1 L/1000 ml x 0.240 mol/L = 0.003048 moles Ba(OH)2

That means we need 2 x 0.003048 moles of HCl = 0.006096 moles HCl needed

Since this # of moles is present in 25.00 ml (0.025 L) of the HCl solution, we can now express the concentration of HCl as [HCl] = 0.006096 moles/0.025 L = 0.244 mol/L = 0.244 M (to 3 sig. figs.)