5.6 Tests for Cations Flashcards

1
Q

What does the term ‘cation’ mean?

A

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

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2
Q

Nearly all cations are _____ ions.

A

metals

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3
Q

What are the two groups of tests for cations?

A
  • The flame tests
  • The metal hydroxide tests
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4
Q

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

A
  • 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
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5
Q

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

A

Blue part of the flame

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6
Q

What colour do Lithium ions cause the flame to turn?

A

Crimson

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7
Q

What colour do Sodium ions cause the flame to turn?

A

Yellow

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8
Q

What colour do Potassium ions cause the flame to turn?

A

Lilac

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9
Q

What colour do Lithium ions cause the flame to turn?

A

Orange-red

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10
Q

What colour do Copper ions cause the flame to turn?

A

Green

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11
Q

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

A

hydroxides, insoluble, hydroxides

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12
Q

Describe how to do the metal hydroxide test for cations

A
  • 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.
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13
Q

What colour precipitate do Calcium ions form?

A

White

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14
Q

What colour precipitate do Copper(II) ions form?

A

Blue

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15
Q

What colour precipitate do Iron(II) ions form?

A

Green

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16
Q

What colour precipitate do Iron (III) ions form?

A

Brown

17
Q

What colour precipitate do Zinc ions form?

A

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