Tests for Ions

Question 1

Describe how to carry out a flame test.

Answer 1

• Dip a nichrome wire loop in concentrated hydrochloric acid.
• Then dip the wire loop into the sample of the compound.
• Hold the loop in the clear blue part of the bunsen burner.
• Observe the colour change in the flame.

Question 2

Name the two substances you need to add to a sample to test for sulfates.

Answer 2

• Dilute HCl acid

- Barium chloride

Question 3

How could you identify the presence of a halide ion?

Answer 3

• To test for halides, add dilute nitric acid (HNO₃) followed by silver nitrate solution (AgNO₃).
• If a precipitate forms, then a halide is present.

Question 4

Describe a test that can be used to test for carbonates in a solution.
[2 marks]

Answer 4

• Add dilute hydrochloric acid to the solution…
• …and then test to see whether the gas given off is carbon dioxide by bubbling it through limewater. If the limewater goes cloudy, the solution contains carbonates.

Question 5

What colour flame would be produced from a solution of potassium iodide?
[1 mark]

Answer 5

Lilac

Question 6

What colour precipitate would be produced from the reaction of calcium carbonate and sodium hydroxide?
[1 mark]

Answer 6

White

Question 7

A student is given a solution of iron(II) sulfate.
Describe how the student could prove that the solution actually is iron(II) sulfate.
[2 marks]

Answer 7

• Add a few drops of sodium hydroxide to a sample of the solution. If a green precipitate forms, then iron(II) ions are present.
• Then add dilute HCl followed by barium chloride solution to a sample of the solution. A white precipitate will form if sulfate ions are present.