The ratio of the peak areas on a gas chromatogram most accurately reflects which

Question

The ratio of the peak areas on a gas chromatogram most accurately reflects which of the following ratios between the two compounds? (Circle one) Volume ratio Mole ratio Mass ratio None of these The factor that most directly affects retention time of a compound is... (Circle one) Boiling point Melting point Solubility in water Solubility in acetone Which of the following "runs" would be analyzed to determine the Response Factor? (Circle one) Equal volume Equal moles Early fractional Early simple Equal mass The mobile phase in the gas-chromatograph is (Circle one) An inert gas A non-volatile liquid A flammable solid *For questions 6-10, assume that we have a mixture with a volume ratio of 50:50 Pentane: Cyclohexane. The boiling point of pentane is 36.1 degree C. Imagine that a fractional distillation has been performed on 10 mL of this mixture. You have the following samples: early fractional distillate, late fractional distillate, pure pentane, pure cyclohexane, original (equal volume) mixture, and an equimolar mixture. Imagine that you run your original mixture through GC and you find two large peaks. One peak has a retention time of 2.52 minutes and the other peak has a retention time of 5.30 minutes. a. What is likely the identity of the compound responsible for the first peak? (Circle one) Pentane Cyclohexane b. What is likely the identity of the compound responsible for the second peak? (Circle one) Pentane Cyclohexane Which sample would you run to check your answers to question 6? In other words, which sample would you run to determine the retention time for ... Pentane? ____ Cyclohexane? ____

Explanation / Answer

4) Boiling point. Substance with low boiling point will remain in gas phase for a longer period and hence will have low retention time

5) An inert gas : liquid nitrogen or helium etc

6) The lower retention time will be of pentane, so first peak for pentane

b) the higher retention time will be of cyclohexane, so second peak for cyclohexane

7) with higher retention time: cyclohexane

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