Calculate the pH of the solution. (The temperature of the solution is 25 C.)

Question

A chemist dissolves 752. mg of pure sodium hydroxide in enough water to make up 180. mL of solution. Calculate the pH of the solution. (The temperature of the solution is 

25 C.)

Round your answer to 3 significant decimal places. 

Answer 1

molar mass NaOH = 40.0 g/mol

752 mg NaOH x 1 g / 1000 mg = 0.752 g NaOH

0.752 g NaOH x 1 mol NaOH / 40.0 g = 0.0188 mols NaOH

0.0188 mols NaOH / 180 ml x 1000 ml / L = 0.10444 mol/L

pOH = -log [OH-] = -log 0.10444

pOH = 0.9811

pH = 14 - pOH

pH = 14 - 0.9811

pH = 13.0 (3 sig.figs.) not to 3 significan decimal places. That would be inane.