SC25 Qualitative Analysis : Test for Ions

Question 1

Flame tests for metal ions

Answer 1

Lithium = red
Sodium = yellow
Potassium = lilac
Calcium = orange-red
Copper = blue-green

Question 2

What is flame photometry?

Answer 2

Allows you to identify ions in a dilute solution. Each ion produces a unique line spectrum with different lines present in different places

Question 3

How do you find the concentration of metal ions?

Answer 3

The intensity of the measured wavelength indicates the concentration of that ion in solution

Question 4

Advantages of instrumental analysis (machines)

Answer 4

• Very sensitive
• Very fast and tests can be automated
• Very accurate

Question 5

How do you identify carbonate ions?

Answer 5

Using Dilute Acid

If carbonate ions are present, the mixture will fizz in dilute acid

Question 6

How do you identify halide ion?

Answer 6

Use Silver Nitrate Solutions

A chloride gives a white precipitate of silver chloride
A bromide gives a cream precipitate of silver bromide
A iodide gives a yellow precipitate of silver iodide

Question 7

How do you identify sulfate ions?

Answer 7

Use Barium Chloride Solution

Add some dilute hydrochloric acid to test sample, and then add some barium chloride solution. If sulfate ions are present, a white precipitate will form

Question 8

Why must the test for each ion be unique?

Answer 8

Each test is unique - it gives certain results depending on the ions present, and each response is different

Question 9

List metal hydroxide precipitate colours

Answer 9

Aluminium = white at first, then colourless
Calcium = white
Copper = blue
Iron (II) = green
Iron (III) = brown

Question 10

How do you identify metal ions using sodium hydroxide solution?

Answer 10

1) Add a few drops of sodium hydroxide solution to a solution of your mystery compound
2) If a hydroxide precipitate forms, you can use its colour to tell which metal ion was in the compound

Question 11

How do you identify ammonium ions and ammonia?

Answer 11

1) To detect ammonium ions, add sodium hydroxide solution and gently heat it
2) If ammonia gas is given off, it means that there are ammonium ions in your mystery substance

1) To test for ammonium gas, hold a piece of damp red litmus paper over it
2) If the mystery gas is ammonia, the litmus paper will turn blue