Question

(a) a sample of solid ca(oh)2 is stirred in water at 30°c until the solution contains as much dissolved ca(oh)2 as it can hold. a 100.-ml sample of this solution is withdrawn and titrated with 5.00 10-2 m hbr. it requires 48.8 ml of the acid solution for neutralization. what is the molarity of the ca(oh)2 solution?

Answer 1

The neutralization reaction is:

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

Therefore based on the reaction stoichiometry, the ratio of Ca(OH)2 : HBr = 1:2

Titration data:

Concentration of HBr = 5.00 *10^-2 M

Volume of HBr required  = 48.8 ml = 0.0488 L

# moles of HBr = 5.00 *10^-2 moles L-1 * 0.0488 L = 0.00244 moles

Based on the reaction stoichiometry:

Moles of Ca(OH)2 = 1/2 * Moles of HBr = 1/2 * 0.00244 = 0.00122 moles

Volume of Ca(OH)2 taken = 100 ml = 0.1 L

Concentration of Ca(OH)2 = 0.00122/0.1

 = 0.0122 M = 1.22 * 10^-2 M