Chromatography

A student uses paper chromatography to investigate the dyes in five different inks, V, W, X, Y and Z.

The chromatogram shows the results of the investigation.

solvent front

V W X Y Z

Explain why the start line on the paper is drawn in pencil rather than in ink.

Explain which two inks contain the dye that is most soluble in the solvent.

Explain how the chromatogram shows that

• W contains only one dye

• V may contain more than one dye

Calculate the R_f value for the dye in W.

Give your answer to two significant figures.

A student does an experiment to identify the dyes in inks A, B, C, D and E.

The student uses this apparatus.

• a piece of chromatography paper

• a beaker

• a solvent

• inks A, B, C, D and E

Describe how the student should set up the apparatus and do the experiment.

You may use a diagram to help your answer.

The chromatogram shows the results for inks A, B, C, D and E.

Explain which ink contains a dye that is insoluble in the solvent.

Explain which inks contain the same dye.

Describe how the student can use the chromatogram to determine the R_f value for the dye in ink C.

You do not need to calculate the R_f value.

Chromatography is used to separate the components in a mixture.

Diagram 1 shows the apparatus used to separate the different dyes in a food colouring.

Diagram 1

Complete the diagram by adding the missing labels.

Give a reason why the baseline is drawn in pencil.

Diagram 2 shows a chromatogram produced from four different food colourings, W, X, Y and Z.

Which two food colourings contain the same dye?

Calculate the R_f value of the dye in food colouring W.

This question is about mixtures and compounds.

The box gives some techniques used to separate mixtures.

The table lists some substances and mixtures.

Complete the table using words from the box to show the best technique to obtain the named substance from each mixture.

Each technique may be used once, more than once or not at all.

State how the box represents a mixture.

Food colourings are mixtures of food dyes.

A student uses paper chromatography to separate the food dyes contained in food colouring D.

The student places spots of three food dyes A, B and C and food colouring D on chromatography paper.

The diagram shows the appearance of the paper after the experiment.

Describe the composition of food colouring D.

A compound has the formula Ca(HCO₃)₂

Determine the number of different elements in Ca(HCO₃)₂

Determine the number of atoms in the formula of Ca(HCO₃)₂

A student uses this apparatus to investigate the dyes in a food colouring A.

Explain two mistakes that the student makes when setting up the apparatus.

The student repeats the experiment, but with no mistakes.

The table shows the R_f values for the two dyes in food colouring A.

Complete the chromatogram for food colouring A by adding and labelling the dyes.

Give a reason why the blue dye has a larger R_f value than the yellow dye.

The diagram shows a chromatogram of the food dyes in four different food colourings, A, B, C and D.

Give the letter of the food colouring that contains three different food dyes.

Give the letters of the two food colourings that contain the same dye.

Using the scale on the diagram, determine the R_f value of the dye in food colouring C.

Give a reason why the dye in food colouring D moves the furthest from the start line.

Describe how a student could obtain a chromatogram similar to the one shown in the diagram.

A student does a chromatography experiment using ink 1, ink 2, and three known dyes A, B and C. The student uses water as the solvent.

The diagram shows the student’s chromatogram.

Deduce what conclusions can be made about the composition of ink 1.

Give one conclusion that can be made about ink 2.

Suggest how the student could change the experiment to find the composition of ink 2.

Calculate the R_f value of dye C, giving your answer to 2 significant figures.

In a chromatography experiment a student uses samples of three pure food dyes, blue (B), red (R) and yellow (Y).

He also uses samples of four unknown substances, S, T, U and V.

The student puts a small drop of each substance on the pencil line.

The diagram shows the student’s chromatogram at the end of the experiment.

solvent front at end

pencil line

B R Y S T U V

at start

Which of the unknown substances contains only one food dye?

Explain which pure food dyes are in substance V.

Calculate the R_f value of the yellow food dye Y.

State how the chromatogram suggests that the yellow food dye Y is less soluble in the solvent than the red food dye R.

Chromatography is used to analyse mixtures.

A student does a chromatography experiment to analyse the composition of green food colouring in sweets.

She places four known dyes, A, B, C and D, and the green food colouring on chromatography paper.

The diagram shows the student’s apparatus at the start of her experiment.

The diagram shows that the student makes two mistakes when setting up her apparatus.

State the two changes that the student should make so that her experiment works.

Another student does the chromatography experiment correctly.

The diagram shows her chromatogram at the end of the experiment.

Explain what the chromatogram shows about the composition of the green food colouring.

The distance between the start line and the spot for dye C is 6.2 cm.

Calculate the R_f value of dye C.

Suggest why dye A does not move.