⭐⭐⭐⭐ Very common for observation and practical questions.
Typical marks
3–10 marks depending on the question.
2. Aim
To identify metal ions in compounds by observing the characteristic flame colour produced when the sample is heated strongly in a Bunsen burner flame.
3. Quick Theory
Metal ions produce characteristic flame colours because heat energy excites electrons to higher energy levels. When the electrons fall back to lower energy levels, they release energy as visible light.
Example:
Sodium ions produce a strong yellow flame. Copper ions produce a blue-green flame.
Examiner Tip: In exams, flame tests usually test the metal ion, not the negative ion.
4. Apparatus and Chemicals
Apparatus
Chemicals/Reagents
Bunsen burner, heatproof mat, nichrome wire loop or wooden splint, watch glass, test tube rack, safety goggles.
Concentrated or dilute hydrochloric acid for cleaning, metal salt samples such as sodium chloride, potassium chloride, calcium chloride, barium chloride, copper sulfate.
Safety: Wear goggles. Tie back long hair. Hydrochloric acid is corrosive/irritant. Bunsen flames are hot and may be almost invisible in bright light.
5. Labelled Experiment Diagram
Flame Test Setup
6. Procedure
Place a small quantity of the metal salt sample on a watch glass.
Clean the nichrome wire loop by dipping it into hydrochloric acid.
Place the wire loop in the hottest part of the Bunsen flame until no colour is seen.
Dip the clean wire loop into the metal salt sample.
Place the sample on the loop into the non-luminous flame.
Observe and record the flame colour immediately.
Clean the wire loop again before testing a different sample.
Repeat using known samples if comparison is required.
Examiner Tip: The wire must be cleaned between tests to avoid contamination and mixed colours.
7. Observation Table
Metal Ion
Flame Colour
Memory Hook
Lithium, Li⁺
Crimson red
Lithium = lovely red.
Sodium, Na⁺
Yellow / golden yellow
Sodium street lamps look yellow.
Potassium, K⁺
Lilac
Potassium = pale purple/lilac.
Calcium, Ca²⁺
Brick red / orange-red
Calcium = brick red.
Barium, Ba²⁺
Apple green
Barium = bright green.
Copper, Cu²⁺
Blue-green
Copper compounds often show blue/green colours.
Examiner Trap: Potassium is usually described as lilac, not simply “purple”. Barium is apple green, not blue-green.
8. Why Hydrochloric Acid Is Used
Hydrochloric acid is used to clean the wire loop and remove traces of previous samples. It also helps some metal compounds form more volatile chlorides, which give clearer flame colours.
Examiner Tip: The most important exam point is: HCl removes contamination from the wire loop.
9. Sources of Error and Improvements
Source of Error
Effect
Improvement
Wire not cleaned properly
Wrong or mixed flame colour.
Clean with HCl and heat until no colour is seen.
Sodium contamination
Strong yellow colour masks other colours.
Use clean apparatus and small samples; compare carefully.
Too much sample on wire
Flame may be smoky or colour too intense.
Use a small amount of sample.
Observing in bright light
Pale colours such as lilac may be hard to see.
Observe against a darker background if safe.
Using luminous flame
Yellow flame may interfere with observation.
Use a non-luminous blue flame.
10. Student Common Mistakes
Not cleaning the wire between samples.
Writing purple instead of lilac for potassium.
Confusing calcium brick red with lithium crimson red.
Confusing barium apple green with copper blue-green.
Using too much sample and producing unclear flame colours.
Forgetting that flame tests identify metal ions.
Writing only the colour without naming the ion.
11. Examiner Tips
Tip 1: Always write the ion and the flame colour together.
Tip 2: Sodium contamination is common because sodium gives a very strong yellow flame.
Tip 3: Use precise colour names: lilac, brick red, apple green, blue-green.
Tip 4: If asked for the reason for HCl, say it cleans the wire/removes contamination.
12. Examiner Traps
Trap: Potassium is lilac, not dark purple.
Trap: Barium is apple green; copper is blue-green.
Trap: Flame tests identify metal cations, not anions.
Trap: A dirty wire may show sodium yellow even when sodium is not the main ion in the sample.
Choose whether the wire is cleaned, perform the flame test, then identify the metal ion.
Current sample:Unknown Sample A
Preparation
Identify the Metal Ion
Observation Window
?
Clean the wire, then perform the test.
Detective Score: 0/0
Simulator Notes
If the wire is not cleaned, contamination may hide the correct colour.
Use the flame colour before choosing the metal ion.
Some colours are similar, so precise colour names matter.
14. Past Paper Style Questions
State the aim of a flame test. [2 marks]
Why is the nichrome wire cleaned with hydrochloric acid before testing a sample? [2 marks]
A sample gives a lilac flame. Identify the metal ion. [2 marks]
A sample gives a blue-green flame. Identify the metal ion. [2 marks]
Describe how you would carry out a flame test on an unknown solid. [5 marks]
Give two sources of error in flame tests and one improvement for each. [4 marks]
15. Mark Scheme Answers
Q1. To identify metal ions [1] using characteristic flame colours [1].
Q2. Hydrochloric acid cleans the wire [1] and removes contamination/previous sample [1].
Q3. Potassium ion / K+ [2].
Q4. Copper ion / Cu2+ [2].
Q5. Clean wire with HCl [1]; heat until no colour is seen [1]; dip into sample [1]; place sample in non-luminous flame [1]; observe and record flame colour [1].
Q6. Dirty wire gives mixed/wrong colour, so clean with HCl [2]; sodium contamination masks colours, so use clean apparatus/small samples [2]. Other valid answers accepted.
16. Quick Revision Card
Metal Ion
Flame Colour
Lithium, Li⁺
Crimson red
Sodium, Na⁺
Yellow / golden yellow
Potassium, K⁺
Lilac
Calcium, Ca²⁺
Brick red / orange-red
Barium, Ba²⁺
Apple green
Copper, Cu²⁺
Blue-green
17. Mastery Checklist
I can state the aim of flame tests.
I can describe how to clean the wire loop.
I can explain why HCl is used.
I can identify sodium, potassium, calcium and copper from flame colours.
I can distinguish barium apple green from copper blue-green.
I can describe the full procedure in exam language.
I can name common sources of error and improvements.