Chemical Analysis and Instrumental Methods

Question 1

What can paper chromatography be used for?

Answer 1

Separating artificial colours.

Question 2

How does paper chromatography separate artificial colours? (4 points)

Answer 2

1) extract colour from food sample by placing it in a solvent
2) put spots of the colour on a pencil baseline on filter paper
3) roll up the sheet and put it in a beaker with some solvent, keeping the baseline above the level of the solvent
4) the solvent seeps up the paper, taking dyes with it to different places

Question 3

What are some advantages of using machines to identify unknown substances? (3 points)

Answer 3

1) very sensitive
2) very fast
3) very accurate

Question 4

What can gas chromatography be used for?

Answer 4

Identifying substances from compounds.

Question 5

How does gas chromatography do this? (7 points)

Answer 5

1) a gas carries a substance through a solid metal column
2) the substances travel at different speeds so they are separated
3) retention time = time it takes to reach the detector, which can be used to identify the substances
4) the recorder draws a gas chromatograph, number of peaks = number of different compounds
5) position of peaks = retention time
6) can be linked to a mass spectrometer, known as GC-MS, identifies substances leaving the column very accurately
7) the relative molecular mass can be read off from the molecular ion peak