Calculate the [H+] in each of the following acid solutions.

Question

a. 5.00 mL of 0.250 M HClO₄ diluted down to 50.0 mL

b.a solution formed by mixing 10.0 mL of 0.100 M HBr with 30.0 mL of 0.200 M HCl

Answer 1

For (a), use V1M1 = V2M2 where or simply note a 1 to 10 dilution so 0.25 M --> 0.025 M

a). (5.00 ml)(0.250 M) = (50.0 ml)(x M)

x = 0.0250 M

b). Each acid is strong so will ionize completely.

moles H⁺ from HBr = 10.0 ml x 1 L / 1000 ml x 0.100 mol / L = 0.00100 moles H⁺

moles H⁺ from HCl = 30.0 ml x 1 L / 1000 ml x 0.200 mol / L = 0.00600 moles H⁺

total moles H⁺ = 0.00100 + 0.00600 = 0.00700 moles H⁺

total volume = 10.0 ml + 30.0 mls = 40.0 mls = 0.0400 L

[H⁺] = 0.00700 mols H⁺ / 0.0400 L = 0.175 mole/L = 0.175 M H⁺