Question

104g of calcium oxide dissolved in 1 l of water. Calculate the concentration of OH- ions in the solution.

Answer 1

n(CaO)=m/M=104/56=1.86(mol).

When CaO is dissolved in water, Ca(OH)₂ is formed:

CaO+H₂O=Ca(OH)₂.

It can be seen that number of moles of Ca(OH)₂ is equal to the number of moles of CaO.

C(Ca(OH)₂)=n/V=1.86/1=1.86(mol/L).

But concentration of OH^- ions is two times higher:

C(OH^-)=2×1.86=3.72(mol/L).