Inorganic Analysis - Inorganic (4)

Question 1

How would you test for carbonate and hydrogencarbonate ions? (1) Give equations (2)

Answer 1

1. Add dilute HCl acid and test whether lime water turns cloudy (CO₂)
2. Carbonate: 2H⁺ + CO₃²⁻ = H₂O + CO₂
3. Hydrogencarbonate: H⁺ + HCO₃⁻ = H₂O + CO₂

Question 2

Explain the test for Sulfate ions (SO₄²⁻). (2) Give ionic equation. (1)

Answer 2

1. Add dilute HCl (aq) then BaCl₂ (aq) & positive test = white ppt.
2. SO₄²⁻ (aq) + Ba²⁺ (aq) = BaSO₄ (s)

Question 3

Explain the test for ammonium ions (NH₄⁺). (2) Give equations. (1)

Answer 3

1. Heat solution with NaOH (aq) and test gas with litmus paper (positive = turns blue)
2. NH₄⁺ + OH⁻ = NH₃ (g) + H₂O

Question 4

What causes different elements to produce different

coloured flames upon burning? (5 points)

Answer 4

1. When heating an atom, some of its electrons are ‘excited’ to a higher energy level
2. When an electron drops to a lower energy level, it emits a quantum of energy
3. The wavelength depends on the difference in the two energy levels
4. We perceive different colours if the wavelength is within the visible light spectrum.
5. Every element has its own characteristic energy levels so different wavelengths will be emitted

Question 5

What are the associated flame colours?

1. Li+
2. Na+
3. K+
4. Rb+
5. Cs+
6. Be2+
7. Mg2+
8. Ca2+
9. Sr2+
10. Ba2+

Answer 5

1. Red
2. Yellow/Orange
3. Lilac
4. Red/Purple
5. Blue/Violet
6. No colour
7. No colour
8. Brick red
9. Crimson red
10. Apple Green

Question 6

What is the experimental procedure for taking a flame test? (4)

Answer 6

1. Take a platinum wire and dip it into HCl acid to clean
2. Place in hottest part of flame, if colour present repeat cleaning procedure
3. Dip in HCl acid and then dip into testing solid. The HCl forms a chloride salt which produces a more vivid colour
4. Place into hottest part of flame and record colour

Question 7

Describe the test for halides (4)

Answer 7

1. Add dilute nitric acid + silver nitrate solution: Cl- = white ppt
   Br- = Cream ppt
   I- = Yellow ppt
2. Nitric acid removes Carbonate which also forms ppt giving false positive
3. Confirm test by adding dilute and concentrated ammonia solution: AgCl = dissolves in dilute ammonia
   AgBr = Dissolves in concentrated ammonia
   AgI = Insoluble
4. Ag+ (aq) plus X- (aq) = AgX (s)