Question

Calculate the molar concentration of a solution 3 molal of ammonia, whose density is 0.98g/ml.

Answer 1

Given:-

→ Molality of the solution = 3 m

→ Density of the solution = 1.98 g/mL

To find:-

→ Molar concentration [molarity] of the solution.

Solution:-

• Molar mass of Nitrogen (N) = 14 g/mol

• Molar mass of Hydrogen (H) = 1 g/mol

Hence, molar mass of ammoinia [NH₃] :-

= 14 + 1×3

= 17 g/mol

Since molality is 3m, thus 3 moles of ammonia are present in 1 kg of solvent.

Mass of NH₃ [solute] in the solution :-

= No of moles × Molar mass

= 3 × 17

= 51g

Total mass of solution :-

= Mass of solute + Mass of solvent

= 51g + 1000g

= 1051g

Volume of the solution :-

= Mass of solution/Density of solution

= 1051/0.98

= 1072.44 mL

= 1.072 L

Molarity of a solution :-

= Moles of solute/Liters of solution

= 3/1.072

= 2.79 M

Thus, molarity of the solution is 2.79M .

Answer 2

Explanation:

Given:-

→ Molality of the solution = 3

→ Density of the solution = 1.98 g/mL

To find:-

→ Molar concentration [molarity] of the solution.

Solution:-

• Molar mass of Nitrogen (N) = 14 g/mol

• Molar mass of Hydrogen (H) = 1 g/mol

Hence, molar mass of ammoinia [NH₃] :-

= 14 + 1×3

= 17 g/mol

Since molality is 3m, thus 3 moles of ammonia are present in 1 kg of solvent.

Mass of NH₃ [solute] in the solution :-

= No of moles × Molar mass

= 3 × 17

= 51g

Total mass of solution :-

= Mass of solute + Mass of solvent

= 51g + 1000g

= 1051g

Volume of the solution :-

= Mass of solution/Density of solution

= 1051/0.98

= 1072.44 mL

= 1.072 L

Molarity of a solution :-

= Moles of solute/Liters of solution

= 3/1.072

= 2.79 M

Thus, molarity of the solution is 2.79M .

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