5.6 Tests for Cations

Question 1

What does the term ‘cation’ mean?

Answer 1

The term ‘cation’ just means a positively charged ion.

Question 2

Nearly all cations are _____ ions.

Answer 2

metals

Question 3

What are the two groups of tests for cations?

Answer 3

• The flame tests
• The metal hydroxide tests

Question 4

Describe how to carry out a flame test to test for cations (4)

Answer 4

• Take a clean platinum or nichrome wire loop by dipping it in some dilute hydrochloric acid, rinsing it in distilled water, and then holding it in a blue flame from a Bunsen burner. The Bunsen burger might change colour for a bit, but once it’s blue again, the loop is clean.
• Dip the wire loop into the compound you want to test.
• Hold the wire in the clear blue part of the Bunsen burner flame (this is the hottest part).
• See what colour the flame turns as the compound burns

Question 5

When performing the flame test, in which part of the flame should you place the wire loop with the metal sample?

Answer 5

Blue part of the flame

Question 6

What colour do Lithium ions cause the flame to turn?

Answer 6

Crimson

Question 7

What colour do Sodium ions cause the flame to turn?

Answer 7

Yellow

Question 8

What colour do Potassium ions cause the flame to turn?

Answer 8

Lilac

Question 9

What colour do Lithium ions cause the flame to turn?

Answer 9

Orange-red

Question 10

What colour do Copper ions cause the flame to turn?

Answer 10

Green

Question 11

Many metal ___________ are ________ and precipitate out of solution when formed. Some of these _____________ have a characteristic colour.

Answer 11

hydroxides, insoluble, hydroxides

Question 12

Describe how to do the metal hydroxide test for cations

Answer 12

• Add a few drops of dilute sodium hydroxide solution to a solution of your mystery compound - all in the hope of forming an insoluble hydroxide.
• If you get a coloured insoluble hydroxide you can often tell which metal was in the compound.

Question 13

What colour precipitate do Calcium ions form?

Answer 13

White

Question 14

What colour precipitate do Copper(II) ions form?

Answer 14

Blue

Question 15

What colour precipitate do Iron(II) ions form?

Answer 15

Green

Question 16

What colour precipitate do Iron (III) ions form?

Answer 16

Brown

Question 17

What colour precipitate do Zinc ions form?

Answer 17

White at first. But then redissolves in excess sodium hydroxide to form a colour solution.