Calculate pH of a solution made by mixing 10 mL of HCl (0.20 M) with 15.0 mL of NaOH (0.10 M).

Answer 1

pH = -log [H⁺], so we have to find [H⁺] in order to find pH.

HCl + NaOH ==> H₂O + NaCl

moles HCl present = 10 ml x 1 L/1000 ml x 0.20 mol/L = 0.002 moles HCl

moles NaOH present = 15 ml x 1 L/1000 ml x 0.10 mol/L = 0.0015 moles NaOH

moles HCl left over after reaction with NaOH = 0.002 - 0.0015 = 0.0005 moles HCl = 0.0005 moles H⁺

Final volume of solution = 10 ml + 15 ml = 25 ml = 0.025 L

[H⁺] = 0.0005 moles / 0.025 L = 0.02 M

pH = -log 0.02

pH = 1.7