Chromatography

Figure 3 shows the changes of state between ice, water and steam.

What is the name of the change of state labelled P in Figure 3?

Which of the following shows the arrangement of particles in ice?

Figure 4 shows the apparatus that can be used to separate a mixture of ethanol and water by fractional distillation.

Name the piece of apparatus labelled R in Figure 4.

Explain the purpose of the piece of apparatus labelled Q in Figure 4.

A student investigates the food dyes used to make the colours W, X, Y and Z in four different sweets.

Figure 5 shows the chromatogram produced.

The solvent front shows how far the solvent moves during the investigation.

Using the information in Figure 5, state which colour is made of only two food dyes.

The R_f value of a spot on the chromatogram can be calculated using the equation R = distance moved by the food dye ^f distance moved by solvent front

Using the information in Figure 5, calculate the R_f value of the food dye labelled S.

Give your answer to 2 decimal places.

R_f value of food dye S =_........

In an experiment, paper chromatography was used to separate the coloured dyes in four different inks, W, X, Y and Z.

Figure 1 shows the chromatogram at the end of the experiment.

The chromatogram shows that only one of the inks contains a single dye.

Which ink contains a single dye?

Which ink contains the greatest number of dyes?

The R_f value of a dye can be calculated using the equation

At the end of the chromatography one dye had moved 3.60 cm and the solvent front had moved 9.20 cm.

Calculate the R_f value for this dye.

Give your answer to 2 decimal places.

R_f =_........

The substance used as the solvent in the chromatography was heated for 8 minutes.

Figure 2 shows how the temperature of the substance changed with time.

From A to B the substance was a liquid.

From C to D the substance was a gas.

Give the name of the change when a liquid becomes a gas.

Use Figure 2 to give the temperature of the substance at 4 minutes.

_........ C

Use Figure 2 to give the time when the substance has completely changed into a gas.

_........ minutes

The temperature of the substance at A was 25C.

Calculate the temperature rise of the substance from A to D.

_........ C

Figure 5 shows the structure of a molecule of compound S.

Use Figure 5 to deduce the empirical formula of compound S.

The melting points of three samples of S are shown in Figure 6.

State whether each of these samples, A, B and C, is pure or impure and justify your answers using the information in Figure 6.

A scientist uses chromatography in an investigation of compound S.

In the conditions used, compound S has an R_f value of 0.22.

Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4 cm.

distance =_........ cm

*(c) A solution of sodium chloride in water needs to be separated to obtain a sample of pure, dry sodium chloride and a sample of pure water.

Figure 7 shows the boiling points of sodium chloride and water.

Explain this difference in boiling points in terms of the structure and bonding of sodium chloride and water and how this difference is used to choose a method to separate sodium chloride solution into pure, dry sodium chloride and pure water.

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.

Draw a labelled diagram of the apparatus used to filter the mixture and collect the sodium chloride solution.

Describe how a sample of pure, dry sodium chloride crystals can be obtained from the filtrate.

Inks contain coloured dyes. Samples of four inks, W, X, Y and Z, were separated using paper chromatography. Figure 3 shows the chromatogram obtained.

In the experiment, the solvent front moved 6.5 cm. Calculate the R_f value of the dye that is present in both inks X and Z.

R_f =_........

State what could be changed in the experiment to make the R_f value more accurate.

In this experiment, ink sample Y did not move from the start line. Explain a change to the experiment that would be needed to separate the dyes in ink sample Y.

Mixtures of substances can be separated using different techniques.

Which of the following is a mixture of substances?

Figure 3 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.

One mistake is that the bulb of the thermometer is too low.

The bulb of the thermometer should be level with the side arm.

Give a reason why the bulb of the thermometer should be level with the side arm.

State one other mistake in Figure 3.

Paper chromatography is used to separate the substances in five different food colourings, P, Q, R, S and T.

Figure 4 shows the chromatogram at the end of the experiment.

The steps needed to carry out the chromatography experiment are listed below. They are not in the correct order.

1 leave the solvent to rise up the paper 2 put solvent in the beaker 3 draw a start line on the piece of paper 4 place the paper in the beaker 5 remove the paper when the solvent is near the top 6 put small spots of the food colourings on the start line

List the steps in the correct order.

The first two steps have been done for you.

Explain, using Figure 4, which food colouring contains the greatest number of coloured substances.

During chromatography of the food colourings, the solvent front moved 8.00 cm and the food colouring R moved 2.30 cm.

Calculate the R_f value for food colouring R. Give your answer to two significant figures.

R_f value =_........

An ink is a mixture of coloured substances dissolved in water.

Which method is used to separate the coloured substances in the ink?

The apparatus shown in Figure 6 can be used to separate water from ink.

Cold water flows through the condenser.

On Figure 6 use arrows to show where the water should flow in and where it should flow out.

Explain why a condenser is used.

The flask was heated with a Bunsen burner.

Give the name of an alternative piece of apparatus that could be used to heat the flask.

The particles in the ink in the flask can be shown as in Figure 7.

In the boxes below, draw the arrangement of particles that would be expected at A and B shown in Figure 6.

Changes of state between the three states of matter are shown in Figure 8.

The changes shown are physical changes.

Explain why these changes are called physical changes rather than chemical changes.