Question

An aqueous solution of magnesium oxalate is prepared by dissolving 4.46 g of magnesium oxalate in 1.51×10² g of water. The density of the solution is 1.01 g mL^-1.

a) Determine the mass percent of magnesium oxalate in the solution.

b) Determine the mole fraction of magnesium oxalate in the solution.

An aqueous solution of nickel(II) chloride is prepared by dissolving 5.61 g of nickel(II) chloride in 4.53×10² g of water. The density of the solution is 1.34 g mL^-1.


Determine the molarity (in mol/L) of nickel(II) chloride in the solution.

Answer 1

Molecular weight of Magnesium oxalate (MgC2O4)= 24+ 2*12+ 64 =112

Mass of sodium oxalate = 4.46 gm

mass of water =1.51*10² =151gm

Total mass = 151+4.46= 155.46

mass percentage of magnesium oxalate= 100*4.46/155.46= 2.87%

Moles of Magnesium oxaalte= Mass/molecular weight = 0.0398

Moles of water = 1.51*100/18 =8.39

Total moles = 0.0398+ 8.39= 8.4298

mole % Magnesium oxalte = 0.0398/8.4298 =0.004271

b) Nickel chloride exists in hexa hydrate whose molecular weight is =238

Moles of 5.61 g of Nickel chloride hex hydrate= 5.61/238= 0.023571 moles

Mass of the solution = mass of water + mass of nickel chloride hexa hydrate= 4.53*102+ 5.61 =453+5.61=458.61gm

Volume of the solution =mass/ density = 458.61 g/1.34(g/ml) =342.24ml =0.342 L

Molarity of the solution = Moles of solute / litre of solution = 0.023571/0.342 M=0.0688M

Alternatively if only nickel chloride is considered , molecular weigh =130

moles of nickel chloride = 5.61/130 =0.043154 moles

Voluue of the solution =0.342 L

Molarity = 0.0431254/0.342 M =0.1261M