C3 Topic 1 Qualitative Analysis

Question 0

Define quantitative analysis.

Give uses.

Answer 0

A test which tells you how much of a chemical is present in a substance.
Breathalyser.

Question 1

Define qualitative analysis.

Give uses.

Answer 1

A test which tells you what is present in a substance.

Blood tests, testing drinking water.

Question 2

How do you test for the positive ions in an ionic compound in the sodium hydroxide test?
What are the results?

Answer 2

1. Add a few drops of sodium hydroxide to the solution.
2. Stir and record the colour of the precipitate formed.

Results:
Calcium (Ca^2+) = White
Aluminium (Al^3+) = White, add more sodium hydroxide and become colourless
Ammonium (NH4^+) = No colour change, heat up and vapour turns Universal Indicator purple/blue, also smells
Copper (Cu^2+) = Blue
Iron II (Fe^2+) = Green
Iron III (Fe^3+) = Brown

Question 3

How do you test for halide ions in an ionic compound?

What are the results?

Answer 3

1. Add dilute nitric acid to the solution.
2. Add silver nitrate to the solution (AgNO3).

Results:
Chloride (Cl-) = White
Bromide (Br-) = Cream
Iodide (I-) = Yellow

Question 4

How do you test for carbonate ions in an ionic compound?

What are the results?

Answer 4

1. Add dilute hydrochloric acid to the solution so that it bubbles.
2. Pass the bubbles through limewater.
3. If carbonate ions are present, the limewater will turn cloudy due to a precipitate being formed.

Question 5

How do you test for sulphate ions in an ionic compound?

What are the results?

Answer 5

1. Add dilute hydrochloric acid to the solution.
2. Add a barium chloride solution to the solution.
3. If sulphate ions are present, the solution will turn white.

Question 6

How do you test for the positive ions in an ionic compound using the flame test?
What are the results?

Answer 6

1. Dip the Nichrome wire into hydrochloric acid.
2. Dip the Nichrome wire into the substance, can be a powder or a solution.
3. Hold Nichrome wire over a lit Bunsen Burner.
4. Record the colour of the flame.

Results:
Sodium (Na+) = Yellow/Orange flame
Potassium (K+) = Lilac flame
Calcium (Ca^2+) = Red flame
Copper (Cu^2+) = Blue/Green flame