Question

The solubility of Potassium Manganate (VII) at 20ºC is 13g per 100g of water and at 90ºC is 60g per 100g of water.

1. Determine the mass of Pottassium (VII) Manganate present in 80g of saturated solution at 90ºC. 
2. Calculate the mass of Pottassium (VII) Manganate that would crystallize out if the solution in (a) were cooled to 20ºC.

Answer 1

1. Determine the mass of Pottassium (VII) Manganate present in 80g of saturated solution at 90ºC. 
   • 60g per 100g of water;total mass of saturated solution = 16g
     160g of saturated solution→13g of KMnO4
     80g of saturated solution→^80x60/₁₆₀ 30g ✓ ½ of KMnO4 
2. Calculate the mass of Pottassium (VII) Manganate that would crystallize out if the solution in (a) were cooled to 20ºC. 
   • At 20ºC:
     113g of saturated solution →13g of KM_nO₄
     80g of saturated solution → 80x13/113=9.204
   • At 90ºC:
     80g of saturated solution →30g of KM_nO₄
     At 200C:80g of saturated solution →9.204g
     Mass of KM_nO₄ crystalizes out
     30-9.204g