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77julia77 [94]
3 years ago
14

A solution contains naphthalene (C10H8) dissolved in hexane (C6H14) at a concentration of 13.06% naphthalene by mass. Calculate

the vapor pressure at 25 ∘C of hexane above the solution. The vapor pressure of pure hexane at 25 ∘C is 151 torr.
Chemistry
1 answer:
worty [1.4K]3 years ago
7 0

Answer: The vapor pressure of the solution at 25^0C is 137 torr

Explanation:

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

\frac{p^o-p_s}{p^o}=i\times x_2

where,

\frac{p^o-p_s}{p^o}= relative lowering in vapor pressure

i = Van'T Hoff factor = 1 (for non electrolytes)

x_2 = mole fraction of solute  =\frac{\text {moles of solute}}{\text {total moles}}

Given : 13.06 g of napthalene is present in 100 g of solution, thus (100-13.06) g = 86.94 g of hexane

moles of solute (napthalene) = \frac{\text{Given mass}}{\text {Molar mass}}=\frac{13.06g}{128g/mol}=0.102moles

moles of solvent (hexane) = \frac{\text{Given mass}}{\text {Molar mass}}=\frac{86.94g}{86g/mol}=1.01moles

Total moles = moles of solute (napthalene)  + moles of solvent (hexane) = 0.102 + 1.01 = 1.112

x_2 = mole fraction of solute (napthalene) =\frac{0.102}{1.112}=0.0917

\frac{151-p_s}{151}=1\times 0.0917

p_s=137torr

Thus the vapor pressure of the solution at 25^0C is 137 torr

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