Question

A solid sample of zinc hydroxide is added to 0.340 L of 0.400 M hydrobromic acid. The solution that remains is still acidic. It is then titrated with 0.400 M sodium hydroxide solution, and it takes 90.5 mL of the sodium hydroxide solution to reach the equivalence point.

What mass of zinc hydroxide was added to the hydrobromic acid solution?

Answer 1

moles HBr = 0.340 x 0.400 = 0.136

moles NaOH = 0.0905 L x 0.400 M = 0.0362

moles HBr used for Zn(OH)2 = 0.136 - 0.0362

                                              = 0.0998

Zn(OH)2 + 2 HBr ------------> ZnBr2 + 2 H2O

moles Zn(OH)2 = 0.0998 / 2 = 0.0499

mass Zn(OH)2 = 0.0499 x 99.4 = 4.96 g

mass Zn(OH)2 = 4.96 g