If 250 milliliters of calcium hydroxide is titrated with 345 milliliters of 0.75 molarity hydrobromic acid, what is the concentration of the base?

The balanced neutralization reaction here is:

Ca(OH)2 + 2HBr --> 2H2O + CaBr2

Notice that two moles of Her are required to neutralize every one mole of Ca(OH)2. This means that for however many moles of Her reacted, HALF as many moles of Ca(OH)2 reacted as well.

Moles of HBr reacted = 0.75 M x 0.345 L = 0.259 mol

Moles of Ca(OH)2 reacted = 0.259 mol / 2 = 0.130 mol

Concentration of Ca(OH)2 = 0.130 mol / 0.250 L = 0.52 M