C1 - Mixtures and Chromatography

Question 1

What is a mixture and what are it’s properties?

Answer 1

• Substances mixed together. They are not chemically bonded.
• They have variable compositions. There is little or no energy change when a mixture forms. They can be separated by physical methods.

Question 2

Can they be separated out by physical methods?

Answer 2

-Yes

Question 3

List physical methods that can separate elements and compounds of a mixture.

Answer 3

• Filtration
• Crystallisation
• Simple distillation
• Fractional distillation
• Chromatography

Question 4

Can you give examples of some mixtures and what they’re a mixture of?

Answer 4

• Air - a mixture of gas.

- Crude oil - a mixture of different length hydrocarbon molecules.

Question 5

What is chromatography and what is it used for?

Answer 5

• A way of separating substances in a mixture.

- It can be used to separate different dyes in an ink.

Question 6

How do you do the chromatography practical?

Answer 6

• Draw a like near the bottom of a sheet of filter paper. Use a pencil to do this (pencil marks are insoluble and won’t dissolve in the solvent).
• Add a spot of the ink to the line and place the sheet in a beaker or solvent with a ruler and paper clips (to keep it in place). A solvent you could use could be water.
• Make sure the ink isn’t touching the solvent.
• Place a kid on top of the container to stop the solvent evaporating.
• The solvent seeks up the paper, carrying the ink with it.
• Each different dye in the ink will move up the paper at different rates, so the dyes will separate out. Each dye will form a spot in a different place - 1 spot per dye in the ink.
• If any of the dyes in the ink are insoluble (won’t dissolve) in the solvent you’ve used, they’ll stay on the baseline.
• When the solvent (water) has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry.
• Draw a like (the solvent front) where the solvent stops on the paper when you took it out.
• The end result is a pattern of spots called a chromatogram.

Question 7

What is a chromatogram?

Answer 7

-A pattern of spots that is the end result of chromatography.

Question 8

How do you calculate the Rf value of a chemical using your chromatography results?

Answer 8

Rf = distance traveled by substance
DIVIDED BY THE
distance traveled by solvent