Question

Density of a 1.5 M solution of urea in water is 1.02
g/mL. The molality of the solution is
1.6 m
1.5 m
0.16 m
16 m​

Answer 1

Answer:

Option 1 is correct ie. 1.6 m

Direct formula is see in

Answer 2

Given:-

→ Molarity of the solution = 1.5 M

→ Density of the solution = 1.02 g/mL

To find:-

→ Molality of the solution

Solution:-

• Chemical formula of urea = CH₄N₂O

• Molar mass of Carbon(C) = 12g

• Molar mass of Hydrogen(H) = 1g

• Molar mass of Nitrogen(N) = 14g

• Molar mass of Oxygen (O) = 16g

Hence, molar mass of urea is :-

= 12 + 1×4 + 14×2 + 16

= 12+4+28+16

= 60g

The relationship between molarity and molality is given by :-

=> m = 1000M/1000ρ - MMₘ

Where:-

• m is molality

• M is molarity

• ρ is density of the solution

• Mₘ is molar mass of solute

=> m = 1000×1.5/[1000×1.02 - 1.5×60]

=> m = 1500/[1020 - 90]

=> m = 1500/930

=> m = 1.6

Thus, molality of the solution is 1.6 m .