Edexcel A-Level Chemistry Paper 1, November 2021: Question 2
3 marks · Easy difficulty · Multiple Choice
Identify the correct apparatus and reagents for a flame test on barium carbonate, the flame colour of barium ions, and the effect of magnesium ions on the barium flame test.
Practise this questionQuestion
Question text
2 Barium ions can be identified by their flame colour.
(a) Which of the following should be used for a flame test on barium carbonate?
(1)
A iron wire and water
B iron wire and concentrated hydrochloric acid
C nichrome wire and water
D nichrome wire and concentrated hydrochloric acid
(b) What colour do barium ions give in a flame test?
(1)
A green
B lilac
C red
D yellow
(c) A flame test was carried out on a mixture of barium chloride and magnesium chloride.
How does the presence of magnesium ions affect the appearance of the flame colour
of barium ions?
(1)
A the colour is more intense
B a bright white colour completely masks the barium colour
C there is no change
D the barium colour is decreased by the white magnesium flame colour
(Total for Question 2 = 3 marks)
Mark scheme
Show the mark scheme
Question
Answer Mark
Number
2(a) The only correct answer is D (nichrome wire and concentrated hydrochloric acid) (1)
A is not correct because iron wire is not used
B is not correct because iron wire is not used
C is not correct because concentrated hydrochloric acid and not water is needed
Question
Answer Mark
Number
2(b) The only correct answer is A (green) (1)
B is not correct because this is the colour for potassium ions
C is not correct because this is the colour for lithium, calcium and strontium ions
D is not correct because this is the colour for sodium ions
Question
Answer Mark
Number
2(c) The only correct answer is C (there is no change) (1)
A is not correct because magnesium ions have no effect on flame colour
B is not correct because the elemental magnesium and not the metal ions give a white colour
D is not correct because magnesium ions have no effect on flame colour
(Total Question 2 = 3 marks)
How to answer it
Identifying Barium Ions via Flame Tests
What this question tests
This question assesses your practical knowledge of Group 2 chemistry, specifically standard analytical procedures for conducting qualitative flame tests, memorised characteristic flame colours for metal ions, and an understanding of how interfering ions affect these observations.
Apparatus for Flame Tests
Which of the following should be used for a flame test on barium carbonate?
✅ Correct Answer: D
nichrome wire and concentrated hydrochloric acid
💡 Key Knowledge
- Nichrome wire: An unreactive alloy (nickel-chromium) that does not give its own distinct colour to the Bunsen burner flame.
- Concentrated HCl: Used to clean the wire and convert metal compounds into volatile metal chlorides, which vaporise readily in the flame.
❌ Common Errors
Choosing iron wire (which is not suitable and can interfere) or using water instead of concentrated hydrochloric acid, which fails to form the necessary volatile chlorides.
Characteristic Flame Colours
What colour do barium ions give in a flame test?
✅ Correct Answer: A
green
💡 Key Knowledge: Recall Checklist
- Barium (Ba²⁺): Green
- Potassium (K⁺): Lilac
- Lithium / Calcium / Strontium: Red / Brick-red / Crimson
- Sodium (Na⁺): Yellow / Orange-yellow
🧠 Exam Technique
Flame colours must be committed to memory. Do not confuse barium's characteristic apple-green flame with copper's blue-green flame or other metal cations.
Interfering Ions in Flame Tests
A flame test was carried out on a mixture of barium chloride and magnesium chloride. How does the presence of magnesium ions affect the appearance of the flame colour of barium ions?
✅ Correct Answer: C
there is no change
💡 Key Knowledge
Magnesium ions do not produce a characteristic colour in a standard Bunsen burner flame test because the energy emitted falls outside the visible light spectrum (or the transition energy is too high). Therefore, they do not interfere with or mask the green colour produced by barium ions.
❌ Common Misconception
Students often confuse magnesium ions in a salt mixture with burning elemental magnesium ribbon (which produces an intense, blinding white light). Magnesium ions in solution/compounds remain invisible in a routine Bunsen flame.
Topics
Inorganic Chemistry · Topic 4: Inorganic Chemistry and the Periodic Table
Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.