Question

What volume of a concentrated HCl solution, which is 36.0% HCl by mass and has a density of 1.179 g/mL, should be used to make 5.30 L of an HCl solution with a pH of 1.5?

Answer 1

[H+] = [HCl] = 10^-1.5 = 0.0316 M

to calculate the molarity of the original HCl solution, and then M1V1 = M2V2

36.0% by mass means that 100 g of the HCl solution will contain 36.0 grams of HCl.

36.0 g HCl / 36.45 g/mol = 0.988 moles HCl in 100 g solution.

The volume of 100 g of solution is: 100 g / 1.179 g/mL = 84.8 mL or 0.0848 L. So, the molarity of the original HCl solution is:

0.988 mol / 0.0848 L = 11.6 M

Now, you can use M1V1 = M2V2:
11.6 M (V1) = 5.30 L (0.0316 M)
V1 = 0.0144 L = 14.4 mL