Question

What volume of a 15.0% by mass NaOH solution, which has a density of 1.116 g/mL, should be used to make 5.10 L of an NaOH solution with a pH of 11.0?

Answer 1

we know that

15.0% by mass NaOH solution means 15 g of NaOH in 100 g of the solvent.

therefore

moles of NaOH = 15 g / 40 g/mol = 0.375 mol

volume of the solution = 100 g / 1.116 g/ml = 89.61 ml

therefore

molarity of the solution = 0.375 mol / 0.08961 L = 4.19 M

and

pH = 11 - means [H3O+] = 10^-11 and [OH-] = 10^-3

therefore molarity of this solution = 10^-3 M

using the molarity equaion , we get

M1 V1 = M2 2V2

V1 = ( 5.10 L x 10^-3 M ) / 4.19 M

= 1.22 x 10^-3 L

= 1.22 mL