Unit 3: 4 - Analysis and Synthesis

Question 1

What colour is the flame when you put Lithium (L⁺) ions into the flame?

Answer 1

Crimson red.

Question 2

What colour is the flame when you put Sodium (Na⁺) ions into the flame?

Answer 2

Yellow.

Question 3

What colour is the flame when you put Potassium (K⁺) ions into the flame?

Answer 3

Lilac.

Question 4

What colour is the flame when you put Calcium (Ca²⁺) ions into the flame?

Answer 4

Red.

Question 5

What colour is the flame when you put Barium (Ba²⁺) ions into the flame?

Answer 5

Green.

Question 6

What is special about the hydroxides of metals with ions that have a ⁺² or ⁺³ charge?

Answer 6

They are insoluble in water.

Question 7

What is special about adding excess sodium hydroxide to aluminium hydroxide compared to adding excess to calcium or magnesium hydroxide?

Answer 7

Aluminium hydroxide dissolves, whereas the others do not.

Question 8

What colour precipitates do aluminium, calcium and magnesium ions form (when mixed with NaOH)?

Answer 8

White.

Question 9

Give a balanced ionic equation for the reaction of Iron (III) ions with hydroxide ions.

Answer 9

Fe³⁺(aq) + 3OH^-(aq) → Fe(OH)₃(s)

Question 10

How do you test for carbonate ions?

Answer 10

Add dilute hydrochloric acid to the substance. If effervescence occurs, bubble the gas through limewater. If it turns cloudy, the substance contains carbonate ions.

Question 11

Write a balanced equation for the reaction of calcium carbonate with dilute hydrochloric acid.

Answer 11

2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g)

Question 12

How do we test a solution for halide ions? Give the results for chloride ions, bromide ions and iodide ions.

Answer 12

Add dilute nitric acid and then silver nitrate to the solution.

• Bromide ions give you a cream precipitate;
• Chloride ions give you a white precipitate;
• Iodide ions give you a yellow precipitate.

Question 13

How do we test a solution for sulphate ions?

Answer 13

Add dilute hydrochloric acid and then barium chloride solution. If a white precipitate forms, sulphate ions are present.

Question 14

Why must we use nitric acid first instead of other acids when testing for halides?

Answer 14

Nitric acid removes interfering ions first (like carbonate ions), and if you used acid like HCl, then it would not react with chlorine.

Question 15

What is a qualitative analysis?

Answer 15

An analysis which simply determines whether or not a substance is in a sample.

Question 16

What is a quantatative analysis?

Answer 16

An analysis which determines how much of a substance is in a sample.