Question

What is the molality of 2 M $HN_3$ solution ? (Density of solution = 1.5g/mL)

Answer 1

Answer:

Molality, m = (1000 - Molarity of solute) / 1000d - Molarity of solution × Molarity of solvent

= (1000 - 42/43) / 1000 × 1.5 - 2 × 42/43

= .................

Solve it and you will get the answer.

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(Expert)

Answer 2

given, concentration of NH3 is 2M.

it means, 2mole of NH3 in 1000mL of solution.

mass of 2mole of NH3 (solute) = 2 × (1 × 3 + 14) = 34g

density of solution is 1.5 g/mL

so, mass of solution = 1000mL × 1.5g/mL

= 1500g

so, mass of solvent = mass of solution-mass of solute

= 1500g - 34g

= 1466g

now, molality = mole of solute/mass of solvent in kg

= 2mole/(1466/1000)kg

= 2 × 1000/1466

= 1.364m

hence, answer is 1.364m