U3-5 - Chemical Analysis

Question 1

State two factors which influence R_f value/retention time.

Answer 1

Polarity
Molecular mass

Accept molecular size

Question 2

What is the relationship between molecular mass and retention time?

Also applies for molecular size

Answer 2

As molecular mass increases, retention time increases.

Heavier molecules travel more slowly = take longer to reach detector

Question 3

How can a gas chromatogram indicate the quantity of substance present?

Answer 3

Area under each peak corresponds to quantity

Bigger area = more of that substance present

Question 4

Mobile phase

Answer 4

Solvent (TLC/paper) or gas (gas chromatography)

Question 5

Stationary phase

Answer 5

Paper/TLC plate
OR high b.p. liquid (gas chromatography)

Question 6

If the mobile phase is ethanol, what type of substance will travel faster: polar or non-polar?

Answer 6

Polar

Ethanol is polar

Question 7

If the mobile phase is helium, what type of substance will travel faster: polar or non-polar?

Answer 7

Non-polar

Helium is non-polar