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Testing for metal ions

L.Intentions:Describe a simple test to identify some metal ions

Accurately record your observations of some tests

Use your results to help you identify the unknown

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Qualitative chemical tests

These tests are simple test tube reactions

that can help us to identify unknown

substances

They tell us nothing about the quantities of

substances just YES or NO!

Describe 3 simple chemical tests you have

come across before

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Qualitative chemical tests

Examples you have seen before are:

Indicators: test for acids/ alkalis (Y7)Lime water: test for carbon dioxide (C1)

Squeaky pop: test for hydrogen (Y7)

Glowing splint relights: test for oxygen (Y7)Bromine water: test for alkenes (C=C) (C1)

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You are going to learn how to test

for positive metal ions, Mx+

Have a look at this!

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You are going to learn how to test

for positive metal ions, Mx+

Some metals (especially in groups 1 & 2)

burn with characteristic flame colours

We can use these colours to identify

them

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You are going to learn how to test

for positive metal ions, Mx+

Some metals (especially in groups 1 & 2)

burn with characteristic flame colours

We can use these colours to identify

them remember lithium?

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You are going to learn how to test

for positive metal ions, Mx+

Some metals (especially in groups 1 & 2)

burn with characteristic flame colours

We can use these colours to identify

them remember lithium? And

potassium?

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You are going to learn how to test

for positive metal ions, Mx+

Some metals (especially in groups 1 & 2)

burn with characteristic flame colours

We can use these colours to identify

them remember lithium? And

potassium? And fireworks?

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Try it yourselves!

Flame tests

1. Clean a wire loop by repeatedly dipping in conc.Hydrochloric acid and heating strongly in a roaringbunsen flame.

2. When the flame is no longer strongly coloured, dip theloop into the acid again then into the metal salt powder.

3. Record the name of the metal ion and the flame colour look very carefully!

4. DO NOT MIX UP THE LOOPS!

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Flame tests for metal ions

Name of the metal ion Flame colour

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Expected observations

Flame tests

Lithium Red

Potassium Lilac

Barium Apple green Copper Green

Calcium Brick red

Sodium

Orange/ Yellow

How did you do? Any differences?

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Evaluation

Were there any difficulties carrying out thesetests?

Were any of the colours difficult to distinguish?

Compare your results with some others. Did

different groups describe any of the colours

differently? Are the results REPRODUCIBLE?

How could these problems be overcome?

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Can you use this knowledge?

Identify the positive ions present in the

unknown compound

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Can you use this knowledge?

Identify the positive ions present in the

unknown compound

Lithium Ions, Li+

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Testing for metal ions

L.Intentions:Describe a simple test to identify some metal ions

Accurately record your observations of some tests

Use your results to help you identify the unknown

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Have we successfully identified the

unknown compound?

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Have we successfully identified the

unknown compound?

No

So what else do we need to know?

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Have we successfully identified the

unknown compound?

No

So what else do we need to know?

The identity of the NON-METAL ions in thecompound

Next Steps:

How to identify NEGATIVE ions.