Question

A solution contains Al3+ and Co2+. The addition of 0.3969 L of 1.658 M NaOH results in the complete precipitation of the ions as Al(OH), and Co(OH)2. The total mass of the precipitate is 23.64 g. Find the masses of Alt and Co2+ in the solution. mass of A1P+: mass of Co2+: g

Answer 1

The balanced chemical reactions are

3NaOH + Al -> Al(OH)3 + 3Na

2NaOH + Co -> Co(OH)2 + 2Na

Total moles of NaOH reacted= volume × molarity

= 0.3969× 1.658

= 0.6580 moles

Let x moles of NaOH reacted with Al and y moles of NaOH reacted with Co.

Total mass of precipitate = 23.64 grams

Mass of Al(OH)3 produced = 78x/3 (by using the equation)

Mass of Co(OH)2 produced = 93y/2 ( using the equation)

As complete precipitation takes place so x+y= 0.658

And 78x/3 + 93y/2 = 23.64

Solving for x and y from the above 2 equations we get

x= 0.3394

y= 0.3186

So mass of Al in solution =( 0.3394/3) × 27 = 3.0545grams

Mass of Co = (0.3186/2) × 59= 9.3987 grams.

I hope this helps....