CHEMCA Free Chemistry Notes for JEE NEET Chemistry MadeEasy: Ostwald-Walker Method

Ostwald-Walker Method - Virtual Lab

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Set A: Solution Bulbs
Loss $\propto p_s$

Loss: 0.000 g

Set B: Solvent Bulbs
Loss $\propto (p^\circ - p_s)$

Loss: 0.000 g

Set C: U-Tube ($CaCl_2$)
Gain $\propto p^\circ$

Gain: 0.000 g

Relative Lowering of VP

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The Ostwald-Walker method measures the relative lowering of vapor pressure dynamically by passing dry air through a sequence of bulbs.

Dry air absorbs vapor until saturated to $p_s$.
Mass Loss ($w_1$) $\propto p_s$

Air absorbs more vapor to reach $p^\circ$.
Mass Loss ($w_2$) $\propto (p^\circ - p_s)$

Anhydrous $CaCl_2$ absorbs all moisture.
Total Mass Gain ($W$) $\propto p^\circ$

JEE/NEET Core Formula:
$$\frac{p^\circ - p_s}{p^\circ} = \frac{w_2}{W} = \frac{\text{Loss in Set B}}{\text{Gain in Set C}}$$

Relative Lowering (RLVP) = 0.000

Solute Mole Fraction ($X_{solute}$) 0.20

Increasing solute concentration lowers the vapor pressure of the solution ($p_s$).