A student took 100 mL of a solution of Mg(OH)2 and reacted it with H2SO4 (aq) to calculate the concentration of hydroxide ions in the solution. If 13.75 mL of 0.010 M H2SO4 was used to react with all of the OH- (aq) in the 100-mL solution, what was the concentration of hydroxide ions dissolved in the 100-mL solution?

Question

A student took 100 mL of a solution of Mg(OH)2 and reacted it with H2SO4 (aq) to calculate the concentration of hydroxide ions in the solution.  If 13.75 mL of 0.010 M H2SO4 was used to react with all of the OH- (aq) in the 100-mL solution, what was the concentration of hydroxide ions dissolved in the 100-mL solution?

DrBob222 · Answer

Ca(OH)2 + H2SO4 ==> CaSO4 + 2H2O

mols H2SO4 = M x L = approx 1.5E-4 but that's an estimate and you need a more accurate answer for this and all the calculations that follow.
So mols OH^- must be twice that and (OH^-) = mols OH^-/L. Note L is 0.1 for Ca(OH)2.