Question

What is the vapor pressure at 23 degC of a solution of 1.20 of haphtalene, C10H8 in 25.6g of benzene C6H6? The vapor pressure of pure benzene at 23 degC is 86.0mmHg. The vapor pressure of the haphtalene can be neglected. Calculate the vapor pressure lowering the solution.

Please show all steps

Thank you!

Answer 1

T = 23°C P° = 86 mm Hg

since this is nonvolatile then we can use ideal depression point equation

Apply

dP = xsolute * P°solvent

xsolute = mol of solute / total mol

m = 1.2 g of naphtalene

MW = 128.1705

mol = 1.2/128.1705 = 0.00936252881

m = 25.6 g of benzene

MW = 78.11

mol = 25.6/78.11 = 0.32774

total mol = 0.3277+0.009363 = 0.337063

x solute = 0.009363 /0.337063 = 0.027778

then

dP = xsolute * P°solvent = 0.027778*86 = 2.388908mm Hg

Pmix = P°solvent - dP = 86-2.388908 = 83.611092 mm Hg