Question

A solution contains Al3+ and Co2+. The addition of 0.3628 L of 1.714 M NaOH results in the complete precipitation of the ions as Al(OH)3 and Co(OH)2. The total mass of the precipitate is 21.96 g. Find the masses of Al3+ and Co2+ in the solution.

Answer 1

Moles of NaOH = Malarity o volume - 1.714 x 0.3628 = 0.6218 Moles of Oh ions furnish by Na oh = 0.6218 moles : If there are 5 moles of NaOH then 3 mdes Oh utilised by 913+ - and 2 moles utilised by Co 2+ i Out of 0.6218 mol Ott - • Utilised by A134- x0.6218 = 0.373 moles OHS • Utilised by Co2+ - - Şx 0.6218 = 0.249 moles OH

a Criven mass of precipitate = 21.969 let mass of Alloh), is x g then mass of Co (OH)₂ = (21096-1) g i Molar mass of Alloh) = 27+ 3(1671) = 78 glmol Molar mass of Color = 59*+2 (16+1) = 93 g/mol • Moles of Allow)? = (moles of ow" Wilised) 40.373 Mass of Alloh), = = moles y molar mass s373 x 78 =0.373 x 26 = 9.698 g Mass of ColoHl2 = (21.96-2) = 21096-9.698 = 12.262 g

The total moles of hydroxide ions furnished by NaOH are utilised by Al​​​​​3+ and Co​​​2+ in 3:2 ratio.