Chromatography

A student investigated three inks using chromatography.

The three inks used were A, B and C.

Inks contain different coloured dyes.

Figure 2 shows the apparatus.

The student used water as the solvent and then repeated the investigation with alcohol as the solvent.

With water as the solvent, the dyes in each ink did not separate.

With alcohol as the solvent, the dyes in each ink did separate.

Why did the chromatography not work when water was used as the solvent?

Tick (✓) one box.

The inks were insoluble in water.

Water moved up the paper too slowly.

Water reacted with the paper.

Give one safety precaution the student should use when pouring alcohol into a beaker.

Why is the start line drawn in pencil and not in ink?

Tick (✓) one box.

A pencil line can be removed after the investigation.

A pencil line will not move up the paper.

The pencil is a different colour from the three inks.

The student used alcohol as the solvent.

Figure 3 shows the results after 10 minutes.

Which ink contained three dyes?

Tick (✓) one box.

A B C

In a different investigation, the distance moved by a dye was 2.4 cm.

What was the distance moved by the dye in millimetres?

The distance moved by the solvent was 80 mm.

Calculate the R_f value of the dye.

Use your answer from Question 02.5.

Use the equation:

This question is about chromatography.

Explain how paper chromatography separates mixtures of coloured substances.

You should identify:

the mobile phase

the stationary phase.

Do not describe how to do the experiment.

A substance has an R_f value of 0.30

The solvent moved 8.0 cm from the start line.

Calculate the distance moved by the substance.

Give your answer in millimetres.

Describe how paper chromatography can be used to identify an unknown substance.

Do not describe how to do the experiment.

A species of grass has the binomial name Lolium perenne.

What is the genus of the grass?

Grass leaves look green because of a green pigment found in chloroplasts.

Name the green pigment found in chloroplasts.

Which mineral ion is found in the green pigment in chloroplasts?

Tick (✓) one box.

Magnesium ion

Nitrate ion

Sodium ion

An area of grass changed colour after being covered by a tent.

The colour of the grass changed from green to yellow.

Figure 13 shows the area of green grass and the area of yellow grass.

A student used paper chromatography to investigate the pigments in grass leaves from: the area of green grass the area of yellow grass.

Figure 14 shows the results.

Figure 14

Distance

Start line

Green Yellow grass grass leaves leaves

The student crushed the grass leaves.

Describe a method to separate the pigments in the crushed grass leaves using paper chromatography.

Figure 14 is repeated below.

Figure 14

Distance

Start line

Green Yellow grass grass leaves leaves

Determine the R_f value of the pigment that is found in green grass leaves but not found in yellow grass leaves.

Use the equation:

R = distance moved by pigment ^f distance moved by solvent

Use Figure 14.

There are fewer pigments in the yellow grass leaves than in the green grass leaves.

Suggest one reason why.

A species of grass has the binomial name Lolium perenne.

What is the genus of the grass?

Grass leaves look green because of a green pigment found in chloroplasts.

Name the green pigment found in chloroplasts.

Which mineral ion is found in the green pigment in chloroplasts?

Tick (✓) one box.

Magnesium ion

Nitrate ion

Sodium ion

An area of grass changed colour after being covered by a tent.

The colour of the grass changed from green to yellow.

Figure 2 shows the area of green grass and the area of yellow grass.

A student used paper chromatography to investigate the pigments in grass leaves from: the area of green grass the area of yellow grass.

Figure 3 shows the results.

Figure 3

Distance

Start line

Green Yellow grass grass leaves leaves

The student crushed the grass leaves.

Describe a method to separate the pigments in the crushed grass leaves using paper chromatography.

Figure 3 is repeated below.

Figure 3

Distance

Start line

Green Yellow grass grass leaves leaves

Determine the R_f value of the pigment that is found in green grass leaves but not found in yellow grass leaves.

Use the equation:

R = distance moved by pigment distance moved by solvent

Use Figure 3.

There are fewer pigments in the yellow grass leaves than in the green grass leaves.

Suggest one reason why.

Some plants have leaves with white areas and green areas.

A student tested a leaf with white areas and green areas for starch.

This is the method used.

1. Boil the leaf in ethanol.

2. Rinse the leaf in water.

3. Add iodine solution to the leaf.

4. Record the colour of each area of the leaf.

Figure 19 shows the results.

The student boiled the leaf in ethanol to remove the green colour from the leaf.

Why does the green colour need to be removed from the leaf before the leaf is tested for starch?

Explain how the results in Figure 19 provide evidence that the white area of the leaf did not contain chlorophyll.

The student investigated the coloured pigments in the leaf.

Figure 20 shows the apparatus.

Chromatography involves a mobile phase and a stationary phase.

Draw one line from each phase to the identity of that phase in the investigation.

The student drew the start line in pencil.

Why did the student not draw the start line in ink?

Table 7 shows the results.

Calculate X in Table 7.

Use the equation:

The distance moved by the solvent was 121 mm.

Give your answer to 2 significant figures.

Table 8 shows the range of R_f values for known leaf pigments.

The student used Table 8 to identify the leaf pigments in their investigation.

Which colour is the leaf pigment phaeophytin?

Use Table 7 and Table 8.

Another student did the investigation using the same leaf pigments.

The R_f values for the same pigments were different.

What is the reason for the difference?

Tick (✓) one box.

A different solvent was used.

A greater volume of solvent was used.

The solvent moved further.

Some plants have leaves with white areas and green areas.

A student tested a leaf with white areas and green areas for starch.

This is the method used.

1. Boil the leaf in ethanol.

2. Rinse the leaf in water.

3. Add iodine solution to the leaf.

4. Record the colour of each area of the leaf.

Figure 2 shows the results.

The student boiled the leaf in ethanol to remove the green colour from the leaf.

Why does the green colour need to be removed from the leaf before the leaf is tested for starch?

Explain how the results in Figure 2 provide evidence that the white area of the leaf did not contain chlorophyll.

The student investigated the coloured pigments in the leaf.

Figure 3 shows the apparatus.

Chromatography involves a mobile phase and a stationary phase.

Draw one line from each phase to the identity of that phase in the investigation.

The student drew the start line in pencil.

Why did the student not draw the start line in ink?

Table 2 shows the results.

Calculate X in Table 2.

Use the equation:

The distance moved by the solvent was 121 mm.

Give your answer to 2 significant figures.

Table 3 shows the range of R_f values for known leaf pigments.

The student used Table 3 to identify the leaf pigments in their investigation.

Which colour is the leaf pigment phaeophytin?

Use Table 2 and Table 3.

Another student did the investigation using the same leaf pigments.

The R_f values for the same pigments were different.

What is the reason for the difference?

Tick (✓) one box.

A different solvent was used.

A greater volume of solvent was used.

The solvent moved further.