Question

1. Calculate the vapor pressure of heptane (b.p. 98.0 ∘C98.0 ∘C) at the gas chromatography column temperature of 94.0 ∘C94.0 ∘C using the form of the Clausius–Clapeyron equation shown

ln(P1P2)=−(ΔHvapR)(1T1−1T2)ln(P1P2)=−(ΔHvapR)(1T1−1T2)

where RR is the ideal gas constant, ΔHvapΔHvap is the enthalpy of vaporization, T1T1 and T2T2 are two different temperatures, and P1P1 and P2P2 are the vapor pressures at the respective temperatures. The enthalpy of vaporization can be estimated using Trouton's rule, ΔH∘vap=(88 J⋅mol−1⋅K−1)×Tbp.ΔHvap∘=(88 J·mol−1⋅K−1)×Tbp.

P=

2. Calculate the vapor pressure of methyl ethyl ketone (b.p. 80.0 ∘C80.0 ∘C) at the same column temperature.

P=

3. For compounds of the same chemical class, what is the relationship between vapor pressure of a compound and retention in gas chromatography?

A. As the vapor pressure decreases, retention time decreases.

B. There is no relationship between vapor pressure and retention.

C. As the vapor pressure increases, retention time increases.

D. As the vapor pressure increases, retention time decreases.

Answer 1