Which of the following is not a pure substance?
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Which of the following is not a pure substance?
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Substances can be pure or they can be mixtures.
Which of these is a mixture?
☐ | A | chlorine | |
☐ | B | sodium | |
☐ | C | sodium chloride | |
☐ | D | sodium chloride solution |
Figure 9 shows some mixtures to be separated and possible methods of separation.
Place a tick () in one box in each row of the table to show the best method to separate the first named substance from each of the mixtures.
method of separation |
substance to separate | crystallisation | filtration | simple distillation |
fractional distillation |
sand from a mixture of sand and sodium chloride solution |
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copper sulfate crystals from copper sulfate solution | ||||
useful liquids from crude oil |
Figure 9
Paper chromatography was used to separate a mixture of blue and red inks. A spot of the mixture was placed on chromatography paper as shown in Figure 10.
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Figure 11
Figure 12
Rf value =
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P, Q, R and S are mixtures of food colourings.
They are investigated using paper chromatography.
Figure 13 shows the chromatogram at the end of the experiment.
Figure 13
☐ | A | mixture P | |
☐ | B | mixture Q | |
☐ | C | mixture R | |
☐ | D | mixture S |
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A student was investigating the colours in black food colouring.
Chromatography was carried out on samples A-E and compared to the black food coloring.
The following chromatogram was produced.
Which of the following conclusions is not true for this chromatogram?
☐ | A | Sample B is insoluble in the solvent used | |
☐ | B | Samples C and D are pure substances | |
☐ | C | Sample D is the least soluble of the samples | |
☐ | D | The black ink is a mixture of A, E and an unknown |
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An ink is a mixture of coloured substances dissolved in water.
Which method is used to separate the coloured substances in the ink?
☐ | A | chromatography | |
☐ | B | crystallisation | |
☐ | C | filtration | |
☐ | D | fractional distillation |
The apparatus shown in Figure 9 can be used to separate water from ink.
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The particles in the ink in the flask can be shown as in Figure 10.
Figure 10
In the boxes below, draw the arrangement of particles that would be expected at A and B shown in Figure 9.
Changes of state between the three states of matter are shown in Figure 11.
The changes shown are physical changes.
Explain why these changes are called physical changes rather than chemical changes.
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A student set up the following apparatus to investigate the colours in three different food colourings.
What are the stationary and mobile phases for this experiment?
Stationary | Mobile | |||
☐ | A | chromatography paper | water | |
☐ | B | beaker | start line | |
☐ | C | water | food colourings | |
☐ | D | start line | chromatography paper |
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Mixtures of substances can be separated using different techniques.
Which of the following is a mixture of substances?
Figure 5 shows the apparatus that a student set up to obtain pure water from ink.
There are three mistakes in the way the apparatus has been set up.
Paper chromatography is used to separate the substances in five different food colourings, P, Q, R, S and T.
Figure 6 shows the chromatogram at the end of the experiment.
List the steps in the correct order.
The first two steps have been done for you.
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A student making copper sulfate crystals used the method below.
Unreacted copper carbonate was left over as it had been added in excess.
Which separation technique could be used to separate the unreacted copper carbonate and solution into different containers?
☐ | A | Filtration | |
☐ | B | Crystallisation | |
☐ | C | Simple distillation | |
☐ | D | Fractional distillation |
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A mixture contains methanol and ethanol. They have different boiling points.
Which method could be used to separate this mixture?
☐ | A | Filtration | |
☐ | B | Simple distillation | |
☐ | C | Crystallisation | |
☐ | D | Evaporation |
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A sample of rock salt contains a mixture of sodium chloride and some insoluble substances.
The rock salt is added to water and the mixture stirred.
The mixture is then filtered to obtain a filtrate of sodium chloride solution.
Inks contain coloured dyes.
Samples of four inks, W, X, Y and Z, were separated using paper chromatography.
Figure 5 shows the chromatogram obtained.
Figure 5
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A student carried out chromatography on a sample of green ink.
The distance moved by the solvent front is 5.8 cm.
The distance moved by the yellow dye is 4.5 cm.
Calculate the Rf value of the yellow dye to 2 significant figures.
☐ | A | 0.78 | |
☐ | B | 0.80 | |
☐ | C | 1.3 | |
☐ | D | 26 |
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During the treatment of ground water, large insoluble particles are allowed to settle to the bottom of a tank.
What is this process called?
☐ | A | Sedimentation | |
☐ | B | Anaerobic digestion | |
☐ | C | Screening | |
☐ | D | Chlorination |
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A sample of potable water contains impurities.
Why is this sample of water potable even though it contains impurities?
☐ | A | the impurities have no smell | |
☐ | B | the impurities are colourless | |
☐ | C | the impurities are harmless | |
☐ | D | the impurities are soluble |
Waste water can be used to produce drinking water.
The processes used include sedimentation, filtration and chlorination.
☐ | A | the waste water is heated so the impurities evaporate | |
☐ | B | the waste water has an acid added to remove impurities | |
☐ | C | the impurities in the waste water settle to the bottom of their container | |
☐ | D | the impurities in the waste water are bleached |
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Some salts can be added to waste water to remove impurities.
In an experiment, different masses of salt A were added to 1000 cm3 samples of waste water.
The experiment was repeated with salt B.
The percentages of impurities removed from the waste water are shown in Figure 10.
Figure 10
It was concluded that the best way to purify 1000 cm3 of the waste water is to add 100 mg of salt B.
Use the information about salt A and salt B in Figure 10 to evaluate this conclusion.
A sample of water was contaminated with a dissolved solid.
Devise a plan to separate pure water from this mixture, including a test to show that the water obtained is neutral.
You may use some or all of the apparatus shown in Figure 11 and any other laboratory apparatus.
Figure 11
Waste water may contain phosphate ions, .
Aluminium ions react with phosphate ions to form aluminium phosphate.
Complete the ionic equation for the formation of aluminium phosphate in this reaction
.................. + → ............
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What is the correct expression for calculating the Rf value in chromatography?
☐ | A | ||
☐ | B | ||
☐ | C | ||
☐ | D |
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