The vapour pressure of pure benzene at a certain temperature is `0.850` bar. A non-volatile, non-electrolyte solid weighting `0.5 g` when added to `39.0 g` of benzene (molar mass `78 g mol^(-1)`). The vapour pressure of the solution then is `0.845` bar. What is the molar mass of the solid substance?

Explanation

To find the molar mass of the non-volatile, non-electrolyte solid added to benzene, we can use the concept of relative lowering of vapor pressure. Here’s the step-by-step solution:

### Step 1: Identify the given data
- Vapor pressure of pure benzene (P₀) = 0.850 bar
- Vapor pressure of the solution (P) = 0.845 bar
- Mass of the solute (solid) = 0.5 g
- Mass of benzene (solvent) = 39.0 g
- Molar mass of benzene (M₁) = 78 g/mol
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