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Tests for Positive Ions.

Tests for Positive Ions. 2.) Qualitative tests. Learning Objectives. By the end of the session: Everyone will have experience of carrying out qualitative tests for positive ions.

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Tests for Positive Ions.

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  1. Tests for Positive Ions. 2.) Qualitative tests.

  2. Learning Objectives. By the end of the session: • Everyone will have experience of carrying out qualitative tests for positive ions. • Most students will be able to identify Aluminium, Calcium, Copper (II), Iron (II), Iron (III) Ammonium and Magnesium ions. • A few students will be able to identify an unknown ion using qualitative tests.

  3. Starter. • We have seen that flame tests allow us to identify some metal ions. • If I try to carry out a flame test on a compound containing Aluminium, Magnesium or Lead, what do you notice? What did we notice about the flame colours of Calcium and Lithium? • Some elements have flame colours which are very similar. This makes them difficult to identify. • Today, we will look at another technique to help us differentiate between compounds which give similar flame tests.

  4. Safety. • Sodium hydroxide is corrosive. • Treat all known and unknown ions as if they were toxic. • Ammonia gas is harmful and should not be inhaled. • Care needed when heating Sodium hydroxide solution.

  5. Qualitative tests.

  6. Qualitative tests. Using the apparatus on the previous slide, this is the procedure for qualitative tests. • Place approximately 1cm3 of the substance under test, in a test tube. • Add 1cm3 of dilute Sodium Hydroxide solution. • Carefully observe. Note your observations. • Repeat steps 2 & 3 twice more.

  7. Observations.

  8. Observations.

  9. Observations. • You should now have a complete set of observations for the test-tube reactions. • Repeat the test for Ammonium ions, but this time, gently heat the test-tube over a Bunsen burner. Hold a piece of damp red litmus paper to the mouth of the test-tube.What do you see? What does this mean? Why moisten the litmus paper?

  10. Unknown substance. • Test the unknown substance with Sodium Hydroxide solution. Note your observations and compare with the results of your experiments. Can you identify the unknown? • X =

  11. Unknown substance. • Test the unknown substance with Sodium Hydroxide solution. Note your observations and compare with the results of your experiments. Can you identify the unknown? • X =

  12. Homework. Use the following observations to identify the unknown ions.

  13. Learning Objectives. By the end of the session: • Everyone will have experience of carrying out qualitative tests for positive ions. • Most students will be able to identify Aluminium, Calcium, Copper (II), Iron (II), Iron (III) Ammonium and Magnesium ions. • A few students will be able to identify an unknown ion using qualitative tests.

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