Question

1g of naphthalene (C10H8) in 50g of certain solvent raise the boiling point by 0.400C. 1.20g of an unknown solute in 60g of same solvent raise the boiling point by 0.550C. What is the molar mass of the solute? ​

Answer 1

Answer:

93

Explanation:

for explanation see the image above

Answer 2

Answer:

The molar mass of an unknown solute is 93.0909 gms.

Explanation:

The formula for elevation in boiling point is ΔTb = (Kb×1000×w₁)/(M₁×W₁)

• ΔTb - an elevation in boiling point
• Kb - molal elevation, ebullioscopic or boiling point constant
• w - the weight of solute
• M - the molar mass of solute
• W - the weight of solvent

1). In the case of naphthalene solute

(ΔTb)₁ = (Kb×1000×w₁)/(M₁×W₁)

0.400℃ = (Kb×1000×1)/(128×50)   [Equation 1]

2). In the case of an unknown solute

(ΔTb)₂= (Kb×1000×w₂)/(M₂×W₂)

0.550℃ = (Kb×1000×1.20)/(M₂×60)  [Equation 2]

Divide equation 1 by equation 2,  

0.400℃/0.550℃ = (M₂×60×1)/(128×50×1.20)

M₂ = 93.0909 gms

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