5.6 Tests for Cations Flashcards
What does the term ‘cation’ mean?
The term ‘cation’ just means a positively charged ion.
Nearly all cations are _____ ions.
metals
What are the two groups of tests for cations?
- The flame tests
- The metal hydroxide tests
Describe how to carry out a flame test to test for cations (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
When performing the flame test, in which part of the flame should you place the wire loop with the metal sample?
Blue part of the flame
What colour do Lithium ions cause the flame to turn?
Crimson
What colour do Sodium ions cause the flame to turn?
Yellow
What colour do Potassium ions cause the flame to turn?
Lilac
What colour do Lithium ions cause the flame to turn?
Orange-red
What colour do Copper ions cause the flame to turn?
Green
Many metal ___________ are ________ and precipitate out of solution when formed. Some of these _____________ have a characteristic colour.
hydroxides, insoluble, hydroxides
Describe how to do the metal hydroxide test for cations
- 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.
What colour precipitate do Calcium ions form?
White
What colour precipitate do Copper(II) ions form?
Blue
What colour precipitate do Iron(II) ions form?
Green
