Question

A solution of glucose in water is labelled as 10 by weight what would be the molality of solution

Answer 1

10%w/w solution of glucose in water means 10 g of glucose present in 100g of solution.

Therefore, Mass of glucose is 10g

Mass of water is = 100g- 10g = 90 g = 0.09 kg

And density = 1.2gmL-1

Let us find molality

Molality = Number of moles of solute / Mass of solvent in Kg

Number of moles of solute  = Mass of glucose / Molar mass of glucose  

Molar mass of glucose (C6H12O6) = 6x12 + 12x1 +  6x16 =180 g /mol

Number of moles of glucose =  10/180  = 0.0556 moles

Molality  =  0.0556/0.09   = 16.7M

Now find the molarity ,

Molarity = Number of moles of solute / Volume of solution in liter

Density = 1.2 g/ml

Volume = mass / density

= 100 g / 1.2 g/ ml  = 83.33 ml = 0.0833 L

Molarity = 0.0556/ 0.0833

= 0.67 M