Instrumental methods

A student investigated an orange dye (A) using paper chromatography.

Figure 4 shows the results of Experiment 1 and Experiment 2 using orange dye A.

Explain why the yellow dye and red dye travel different distances in Experiment 1.

Refer to forces of attraction between the dyes and the chromatography paper in your answer.

The student used the same type of chromatography paper in Experiment 1 and in Experiment 2.

Explain why the yellow dye is in different positions in Experiment 1 and in Experiment 2.

Use Figure 4.

Figure 4 is repeated below.

Figure 4 shows the results of Experiment 1 and Experiment 2 using orange dye A.

The student investigated a different orange dye (B).

Figure 5 shows the results of Experiment 3 using orange dye B.

Compare the purity of the orange dyes A and B.

Give reasons for your answer.

Use Figure 4 and Figure 5.

The student calculated that the R_f value of the orange dye in the experiment shown in Figure 5 was 0.48

Calculate the distance moved by the solvent front when the orange dye had moved 5.4 cm.

Why is the R_f value of a dye not affected by how far the solvent front is allowed to travel?

Another type of chromatography is called gas chromatography.

Gas chromatography is an instrumental method of chemical analysis.

Scientists tested the orange dyes using gas chromatography.

Suggest two advantages of using the instrumental method of gas chromatography rather than paper chromatography.

This question is about chemical analysis.

Potassium bromide is used in medicine.

A scientist tested a sample of medicine to show the presence of potassium ions and of bromide ions.

The sample is soluble in water.

Plan a method the scientist could use to show that the sample of medicine contains potassium ions and bromide ions.

The scientist has:

• a Bunsen burner

• a metal wire

• test tubes

• a dropping pipette

• distilled water

• dilute nitric acid

• silver nitrate solution.

You should give the results of the tests.

The scientist could also use an instrumental method to show the presence of potassium ions in the medicine.

Which instrumental method could be used to show the presence of potassium ions in the medicine?

Give one advantage of using this instrumental method instead of a chemical test.

This question is about chemical analysis. Potassium bromide is used in medicine. A scientist tested a sample of medicine to show the presence of potassium ions and of bromide ions. The sample is soluble in water.

Plan a method the scientist could use to show that the sample of medicine contains potassium ions and bromide ions. The scientist has:

• a Bunsen burner

• a metal wire

• test tubes

• a dropping pipette

• distilled water

• dilute nitric acid

• silver nitrate solution.

You should give the results of the tests.

The scientist could also use an instrumental method to show the presence of potassium ions in the medicine.

Which instrumental method could be used to show the presence of potassium ions in the medicine?

Give one advantage of using this instrumental method instead of a chemical test.

Potash alum is a chemical compound. The formula of potash alum is KAl(SO₄)₂

Give a test to identify the Group 1 metal ion in potash alum. You should include the result of the test.

Name one instrumental method that could identify the Group 1 metal ion and show the concentration of the ion in a solution of potash alum.

A student identifies the other metal ion in potash alum. The student tests a solution of potash alum by adding sodium hydroxide solution until a change is seen.

Give the result of this test.

This test gives the same result for several metal ions. What additional step is needed so that the other metal ion in potash alum can be identified? Give the result of this additional step.

Describe a test to identify the presence of sulfate ions in a solution of potash alum. Give the result of the test.

This question is about chemicals in fireworks. Coloured flames are produced because of the metal ions present in fireworks.

What colour flame would sodium ions produce?

Name a metal ion that would produce a green flame.

Some fireworks contain a mixture of metal ions. Why is it difficult to identify the metal ions from the colour of the flame?

Flame emission spectroscopy is used to identify metal ions in a firework. Figure 1 shows:

• the flame emission spectra of five individual metal ions

• a flame emission spectrum for a mixture of two metal ions.

Which two metal ions are in the mixture? Tick two boxes.

The compounds in fireworks also contain non-metal ions. A scientist tests a solution of the chemicals used in a firework.

Silver nitrate solution and dilute nitric acid are added to the solution. A cream precipitate forms. Which ion is shown to be present by the cream precipitate?

Describe a test to show the presence of sulfate ions in the solution. Give the result of the test if there are sulfate ions in the solution.