Chromatography can be used to test the purity of substances.
The diagram shows the chromatogram of a coloured substance.
How does this chromatogram show that this substance is not pure?
Draw a circle around the correct Rf value for the spot labelled X.
State how a colourless substance can be made visible on a chromatogram.
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Substances can be classified as elements, compounds or mixtures.
Each of the boxes in the diagram represents either an element, a compound or a mixture.
The list gives the names of some methods used in the separation of mixtures:
Use names from the list to choose a suitable method for each separation. Each name may be used once, more than once or not at all.
The colours in three different dyes, A, B & C, were investigated using paper chromatography.
The dyes are soluble in propanone but not soluble in water.
The apparatus used is shown.
Place two ticks in boxes that identify how the equipment was incorrectly set up.Â
| The dyes are all on the same piece of chromatography paper | Â |
| The solvent used is water | Â |
| A lid is on the beaker | Â |
| The water is not level with the dyes | Â |
| The start line is drawn in ink | Â |
The student corrected the mistakes and obtained the chromatogram shown in Figure 2.
Put ticks (✔ ) in the boxes to show which statements are true and which statements are false.Â
| Â | True | False |
|  Dye A is the most soluble |  |  |
| Â Dye C is a mixture | Â | Â |
| Â Dye C contains dye BÂ | Â | Â |
| Â Dye C contains dye A | Â | Â |
| Â Dye B is a pure substance | Â | Â |
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The ester linkage showing all the bonds is drawn as
or more simply it can be written as –COO–.
[1]
[1]
Draw the structural formula of the polyester formed from the following monomers.
You are advised to use the simpler form of the ester linkage.
Esters can be used as solvents in chromatography. The following shows a chromatogram of plant acids.
An ester was used as the solvent and the chromatogram was sprayed with bromothymol blue.
[2]
[1]
| Plant acid | Rf value |
| tartaric acid | 0.22 |
| citric acid | 0.30 |
| oxalic acid | 0.36 |
| malic acid | 0.46 |
| succinic acid | 0.60 |
[2]
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Electrolysis is used to manufacture magnesium from molten magnesium bromide.
The following statements are about the procedure for making crystals of hydrated magnesium bromide from magnesium and dilute hydrobromic acid.
| A |
Add an excess of magnesium to dilute hydrobromic acid. |
| B |
Filter off the crystals and dry between filter papers. |
| C |
Filter off the excess magnesium. |
| D |
Leave the mixture at room temperature to form more crystals. |
| E |
Leave the mixture until no more bubbles are seen. |
| F |
Warm the filtrate to the point of crystallisation. |
Put the statements A, B, C, D, E and F in the correct order.
Magnesium is a metal in Group II of the Periodic Table.
Cobalt is a transition element with a higher melting point and a higher boiling point than magnesium.
Describe two other properties of cobalt which are different from those of magnesium.Â
Chromatography can be used to separate a mixture of ions from different transition element compounds.
Two solutions, Y and Z, each containing only one type of transition element ion were placed on a piece of chromatography paper.
Four samples, R, S, T and U, each containing transition element ions, were also placed on the same piece of chromatography paper.
Â
The results of the chromatography are shown.
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