OCR GCSE Combined Science
Topic questions Chemical analysis Chromatography
11 questions · 40 marks · about 45 minutes
Which type of mixture can be separated using paper chromatography?
A A mixture of gases.
B A mixture of insoluble liquids.
C A mixture of insoluble solids.
D A mixture of soluble liquids.
A student performs a chromatography experiment on a mixture of dyes.
The solvent moves 8.0 cm up the chromatography paper.
The Rf value for one dye is 0.60.
What distance does this dye move up the chromatography paper?
A 4.0 cm
B 4.8 cm
C 6.0 cm
D 7.2 cm
A teacher uses paper chromatography to show which dyes are in four different food colourings, A, B, C and D.
Fig. 14.1 shows the result of their experiment.
Fig. 14.1
Which food colouring contains the most dyes?
Which food colourings contain the same dye?
The teacher repeats the experiment with a new food colouring Q. They find it contains the same dyes that are also found in B and D.
Draw the results for the food colouring Q on Fig. 14.2.
Fig. 14.2
Fig. 14.3 shows the result for the food colouring D.
Fig. 14.3
Calculate the Rf value for the dye in the food colouring.
Give your answer to 2 significant figures.
The diagram shows how paper chromatography can be used to separate the colours in an ink.
What is the solvent called?
A The baseline
B The mobile phase
C The reference phase
D The stationary phase
Thin layer chromatography (TLC) is used to analyse and identify unknown samples.
Fig. 12.1 shows the apparatus used for thin layer chromatography.
Fig. 12.1
Identify the stationary phase and mobile phase shown in Fig. 12.1.
What determines how far the sample travels up the TLC plate?
Tick (✓) one box.
Fig. 12.2 shows the final TLC plate for a sample.
Fig. 12.2
Calculate the Rf value for the sample.
Give your answer to 2 decimal places.
A black ink is a mixture of different colours.
The diagram shows how the colours in the black ink can be separated.
What is the name of this method of separation?
A Chromatography
B Crystallisation
C Distillation
D Filtration
The diagram shows a chromatogram produced by paper chromatography.
What is the Rf value?
A –10
B –5
C 0.67
D 1.5
A scientist wants to find out the amount of each chemical in a mixture.
Which row in the table shows the chromatographic techniques that the scientist could use?
| Paper chromatography | Thin layer chromatography | Gas chromatography | |
| A | ✓ | 7 | 7 |
| B | ✓ | ✓ | 7 |
| C | 7 | 7 | ✓ |
| D | 7 | ✓ | ✓ |
Aspirin is a widely used painkiller and is sold as tablets.
One of the chemicals in aspirin is salicylic acid. The structure of salicylic acid is shown below.
Salicylic acid
What is the empirical formula of salicylic acid?
It is important that aspirin is pure for it to be safely used in tablets.
Explain the meaning of the term pure.
Three students, A, B and C make aspirin and check its purity. The students test the purity of the aspirin by measuring the melting point.
Their results are shown in the table.
| Student | Melting point (°C) |
| A | 160 |
| B | 139 |
| C | 137 |
The melting point of pure aspirin is in the range 138–140 °C.
Which student made pure aspirin?
Tick (✓) one box.
Another method of checking the purity of a substance is paper chromatography.
Look at the diagram of the apparatus used for paper chromatography.
Label the chromatography diagram.
Choose your labels from the list.
active phase
inactive phase
gas phase
mobile phase
stationary phase
* This is the method the students follow for the paper chromatography experiment.
1. Draw a pen line near the bottom of the paper.
2. Put a spot of the substance to be tested onto the line.
3. Stand the paper in the solvent. The solvent should be at the same level as the spot.
4. Cover the beaker.
5. Remove the paper from the beaker before the solvent reaches the top.
6. Calculate the Rf value of the substance by using this equation:
Their teacher notices some mistakes with this method.
Describe and explain the mistakes in the method and suggest improvements that could be made.
12* A student carries out an experiment using paper chromatography to distinguish between three substances.
Here is his method.
1. Draw a pen line half way up the paper.
2. Put a large spot of the substance to be tested onto the line.
3. Stand the paper in the solvent. The solvent should be at the same level as the spot.
4. Leave the beaker uncovered.
5. Remove the paper from the beaker before the solvent reaches the top.
He calculates the Rf value for each substance.
Look at his results.
| Substance | Distance moved by solvent (mm) | Distance moved by spot (mm) | Rf value |
| X | 95 | 78 | 1.22 |
| Y | 95 | 65 | 1.46 |
| Z | 95 | 51 | 1.86 |
His teacher noticed some mistakes with his method and his Rf values.
Describe and explain the mistakes the student has made and suggest corrections.
Memes
Laugh now. Cry in the exam hall later. Then come back and do a past paper.
Mum 💖
which science is it today? 🥰
all of them somehow
go on genius!!! 💪
📱 Screen time this week · YouTube6h 21m
Combined Science starter pack