The vapor pressure of diethyl ether (ether) is 463.57 mm Hg at 25 °C. A nonvolatile, nonelectrolyte that dissolves in diethyl ether is testosterone. Calculate the vapor pressure of the solution at 25 °C when 7.752 grams of testosterone, C19H28O2 (288.4 g/mol), are dissolved in 208.0 grams of diethyl ether. diethyl ether = CH3CH2OCH2CH3 = 74.12 g/mol.

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Answer: The vapor pressure of solution is 459.17 mmHg

Explanation:

To calculate the number of moles, we use the equation:

[tex]\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}[/tex]      .....(1)

  • For testosterone:

Given mass of testosterone = 7.752 g

Molar mass of testosterone = 288.4 g/mol

Putting values in equation 1, we get:

[tex]\text{Moles of testosterone}=\frac{7.752g}{288.4g/mol}=0.027mol[/tex]

  • For diethyl ether:

Given mass of diethyl ether = 208.0 g

Molar mass of diethyl ether = 74.12 g/mol

Putting values in equation 1, we get:

[tex]\text{Moles of diethyl ether}=\frac{208.0g}{74.12g/mol}=2.81mol[/tex]

Mole fraction of a substance is calculated by using the equation:

[tex]\chi_A=\frac{n_A}{n_A+n_B}[/tex]

[tex]\chi_{\text{testosterone}}=\frac{n_{\text{testosterone}}}{n_{\text{testosterone}}+n_{\text{diethyl ether}}}[/tex]

[tex]\chi_{\text{testosterone}}=\frac{0.027}{0.027+2.81}\\\\\chi_{\text{testosterone}}=0.0095[/tex]

The formula for relative lowering of vapor pressure will be:

[tex]\frac{p^o-p_s}{p^o}=i\times \chi_{\text{solute}}[/tex]

where,

[tex]p^o[/tex] = vapor pressure of solvent (diethyl ether) = 463.57 mmHg

[tex]p^s[/tex] = vapor pressure of the solution = ?

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

[tex]\chi_{\text{solute}}[/tex] = mole fraction of solute (testosterone) = 0.0095

Putting values in above equation, we get:

[tex]\frac{463.57-p^s}{463.57}=1\times 0.0095\\\\p^s=459.17mmHg[/tex]

Hence, the vapor pressure of solution is 459.17 mmHg

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