Question

Dissolving `120g` of urea `(Mw = 60)` in `1000 g` of water gave a solution of density `1.15 g mL^(-1)`. The molarity of solution is:
A. `1.78 M`
B. `1.02 M`
C. `0.50 M`
D. `2.05 M`

Answer 1

Correct Answer - D
`n_("urea") = ("Mass"_("urea"))/("Molar mass"_("urea")) = (120g)/(60g mol^(-1)) = 2 "mol"`
Volume of solution `= ("Mass of solution")/("Density of solution")`
`= ((120+1000)g)/(1.15g mL^(-1)) = 974 mL = 0.974 L`
Molarity `= ("Moles of urea")/("Liters of solution") = (2 mol)/(0.974L)`
`= 2.05 "mol" L^(-1) = 2.05M`