A-level chromatography lesson

A-level chromatography lesson

Open Ended

Is silica considered a polar or non polar phase? Explain what this means

Multiple Choice

Which molecule would likely have the longest retention time?

• Ethanol

• Glucose

• Chloromethane

• hexane

Multiple Choice

Which solvent would you add to the eluent to decrease the retention time of a nonpolar sample chemical?

• Ethanol

• water

• propanone

• tetra chloro methane

Multiple Choice

What sould an Rf value always be?

• Great than 1

• Near 1

• less than 1

Open Ended

What does a Rf of close to 1 suggest?

Open Ended

A chemist found that on analysis the 2 spots for glucose and hydroxycyclohexane were too close together what should the chemist do when re running the chromatogram. explain your answer.

Watch the vid

https://www.youtube.com/watch?v=UmWMlKJAdSk

Why is it used?

• Cheap

• can be set up on the bench

• you collect your purified sample unlike TLC

• non distructive tichnique

Draw backs

• Time consuming to setup

• the column can 'go off' if the solvent evaporates from the silica

• quality of separation depends on the quality of the packed column (you are to blame!)

• not anaylitic, you will still have to run TLC, IR, NMR, MS to determine what is in each fraction.

Multiple Choice

WHICH PIGMENT WOULD HAVE BEEN MORE POLAR?

• red

• green

• black

Open Ended

A mixture of pentanal and pentan-1-ol were separating by column chromatography using a silica powder with cyclohexane as eluent. Which substance will have the shortest retention time? Explain your answer.

Key points

• High sensitive

• Separative and Quanitative

• separated samples not retieved from device (destructive technique).

Multiple Choice

Which substance had the longest retentiontiem?

• Nonane

• decane

• Hexane

• Heptane

Fill in the Blank

What spectroscopic technique is used to analyse the fractions from gas Chromatography?

Fill in the Blank

What acronym describes this combined technique?

now complete the assignment (PPQ pack) on Teams