Show graphically how the vapour pressure of a solvent and a solution in it of a non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

Solution

Answer:

Elevation of boiling point with addition of non-volatile solute vapour pressure decrese and hence boiling point increase.

Let $T_{b}^{0}$ be the boiling point of pure solvent and
T_b be the boiling point of solution. The increase in
the boiling point $∆ T_{b} = T_{b} - T_{b}^{0}$ is known as
elevation of boiling point.

for dilute
solutions the elevation of boiling point (ΔTb) is
directly proportional to the molal concentration of
the solute in a solution. Thus

ΔTb ∝ m
or
ΔTb = K_b m

Here m (molality) is the number of moles of solute dissolved in 1 kg of solvent and the constant of proportionality, Kb is called Boiling Point Elevation Constant or Molal Elevation Constant. The unit of K_b is K kg mol-1.If w₂ gram of solute of molar mass M₂is dissolved in w₁ gram of solvent, then molality, m of the solution is given by the expression:

$m = \frac{1000 \times w_{2}}{M_{2} \times w_{1}} putting the value of molality in ∆ T_{b} = K_{b} m we get ∆ T_{b} = \frac{k_{b} \times 1000 \times w_{2}}{M_{2} \times w_{1}}$

Thus, in order to determine M₂, molar mass of the solute, known mass of solute in a known mass of the solvent is taken and ΔT_b is
determined experimentally for a known solvent whose Kb value is known.

Some More Questions From Solutions Chapter

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 37⁰C.

Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

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Solutions

Show graphically how the vapour pressure of a solvent and a solution in it of a non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

Some More Questions From Solutions Chapter

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 37⁰C.

Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

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NCERT Sample Papers

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For Daily Free Study Material Join wiredfaculty

Solutions

Show graphically how the vapour pressure of a solvent and a solution in it of a non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

Some More Questions From Solutions Chapter

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 370C.

Suppose a solid solution is formed between two substances, one whose particles are very large and the other whose particles are very small. What kind of solid solution is this likely to be?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL at 37⁰C.