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Better Equipped Practical Teaching Guides
An enhanced GCSE Chemistry practical guide to carrying out flame tests safely, identifying lithium, sodium, potassium, calcium and copper(II) ions, controlling contamination, interpreting qualitative observations and evaluating the reliability of results.
Teacher note: This resource is provided as a practical support guide to accompany laboratory equipment. Teachers should adapt procedures and risk assessments to suit their curriculum requirements, examination-board specifications and local laboratory policies.
In this practical, students use flame tests to identify different metal ions by observing the distinctive colours they produce when heated in a Bunsen burner flame. A nichrome wire loop is carefully cleaned, used to test a range of known metal salt solutions and then used to investigate unknown samples.
The practical reinforces understanding of electronic structure, electron excitation and the relationship between atomic structure and the periodic table, while developing essential practical skills in observation, qualitative analysis and safe laboratory technique.
Flame tests can be used to identify some metal ions. Heating a sample transfers energy to electrons in metal-containing particles in the flame. The electrons move to higher energy levels. When they return to lower energy levels, they emit light at characteristic wavelengths. The combination of these emitted wavelengths produces the observed flame colour.
Before heating, electrons occupy lower energy levels.
Energy from the Bunsen burner flame is absorbed.
An electron moves to a higher energy level. This excited state is unstable.
As the electron returns to a lower energy level, light is emitted at characteristic wavelengths.
Key idea: characteristic energy-level transitions → characteristic emission wavelengths → an observed flame colour.
Important limitation: flame tests are qualitative. Contamination, mixtures, low concentrations and similar colours can make identification uncertain.
Contamination control: use separate labelled sample vessels and droppers, keep the wire loop clean, avoid touching the loop, allow it to cool before placing it into acid or sample, and test sodium last where practical.
Safe flame sequence: use the yellow safety flame for lighting and standby. Adjust to a stable blue flame for the flame-test observation. Return to the yellow safety flame during pauses and close the air hole before turning off the gas when finished.
Observation tip: a suitable blue or cobalt-glass filter may be used under teacher direction where strong sodium emission masks potassium.
| Unknown sample | Observed flame colour | Metal ion identified | Confidence: high, medium or low |
|---|---|---|---|
| A | |||
| B | |||
| C | |||
| D | |||
| E |
| Solution | Ion | Expected flame colour | Terminology note |
|---|---|---|---|
| Lithium chloride | Li+ | Crimson red | Some examination-board terminology may simply use red. |
| Sodium chloride | Na+ | Bright yellow | Sodium contamination can strongly affect other observations. |
| Potassium chloride | K+ | Lilac | The colour can be masked by sodium contamination. |
| Calcium chloride | Ca2+ | Brick red | Often described as orange-red; use the wording required by the examination board. |
| Copper(II) chloride | Cu2+ | Blue-green | May also be described as green depending on specification wording. |
Interpret cautiously: a single flame colour is supporting evidence rather than proof. Mixtures, contamination and similar colours can make identification uncertain.
Visual reference note: flame photographs are illustrative. Actual flame appearance varies with concentration, flame conditions, room lighting and camera settings.
The known metal-ion solution or unknown sample being tested.
The flame colour observed.
Approximate sample amount, concentration, flame region, observation time, room lighting or background, sample container and procedure.
Clean or replace the loop, use separate labelled droppers, keep samples covered where appropriate, avoid touching the loop and test sodium last where practical.
| Source of error or limitation | Possible effect | Improvement |
|---|---|---|
| Dirty wire loop | Contamination produces mixed or misleading colours. | Clean thoroughly between tests or replace the loop. |
| Sodium contamination | Strong yellow emission may mask other colours, especially potassium. | Use clean apparatus and dedicated droppers and test sodium last where practical. |
| Too much sample | The flame may become bright, unclear or difficult to interpret. | Use only a tiny amount of sample. |
| Bright or cluttered background | Subtle flame colours become difficult to distinguish. | Use a dark viewing card or slightly dimmer lighting while maintaining safe visibility. |
| Different observers | Colour descriptions may be subjective. | Repeat observations and compare with known standards and other observers. |
| Contaminated sample solutions or shared droppers | Additional ions may produce misleading colours. | Use fresh solutions and separate labelled droppers and vessels. |
| Loop placed too high or too low | Weak, faint or distorted colour. | Hold the loop just above the tip of the inner blue cone. |
| Hot loop placed into the sample | May cause splashing, contamination or damage. | Allow the loop to cool before placing it into acid or sample. |
| Low sample concentration | Weak flame colour. | Use fresh, appropriately prepared solutions and compare with known standards. |
| Mixed-ion samples | Overlapping emissions may prevent reliable visual identification. | Use a spectroscope or instrumental emission method where available. |
| Inconsistent observation time | Some colours may be missed because they disappear quickly. | Observe immediately and keep the viewing procedure consistent. |
The method is more valid when known standards and unknown samples are tested under comparable conditions, similar sample amounts and concentrations are used and contamination is controlled. Mixtures, contaminated vessels and inconsistent concentrations reduce validity.
Some metal ions produce characteristic flame colours that can be used as evidence when identifying an unknown sample. The test is not definitive where samples contain mixtures or contamination.
Further improvement: a clean, dedicated platinum loop may reduce some interference, although it is expensive and can still become contaminated. A spectroscope separates emitted light into spectral lines, making comparison more objective and selective.
Topic: Chemical Analysis / Qualitative Analysis / Identification of Ions
This practical supports the flame-test component of AQA Required Practical 7, Pearson Edexcel qualitative analysis and OCR qualitative ion testing. Teachers should adapt the procedure and accepted colour terminology to their examination board and local safety guidance.
| Problem | Possible cause | Solution |
|---|---|---|
| No flame colour | Too little sample; low sample concentration; wrong flame region; loop not properly coated; observation made too late. | Repeat with a tiny fresh sample, check the loop position, compare with a known standard and ask the teacher to check the solution if necessary. |
| Yellow flame every time | Sodium contamination on the loop, sample vessel, dropper or glassware; touching the loop. | Replace or thoroughly clean the loop, use a fresh sample and dedicated dropper, and test sodium last. |
| Flame colours mixed | Contaminated sample solution, genuine mixture of ions or dirty loop. | Clean or replace the loop. Replace contaminated samples and droppers. A genuine mixture may not be reliably identified using a visual flame test. |
| Weak colour | Incorrect flame position, bright background, low sample concentration or insufficient observation time. | Use a stable blue flame, position the loop just above the inner blue cone, repeat with a tiny fresh portion, use a dark viewing card and compare with a known standard. |
| Colour disappears quickly | Normal observation. | Observe immediately and repeat if uncertain. |
“The Bunsen burner changes temperature to make each colour.”
The colour is produced by excited metal-containing particles in the flame, not by a change in Bunsen burner temperature alone.
“All compounds containing the same metal ion produce different flame colours.”
In the standard salts used here, the metal ion is primarily responsible for the characteristic flame colour. The other ion and physical form can still affect intensity and ease of observation.
“Hydrochloric acid produces the flame colour.”
Hydrochloric acid is used to clean the loop and remove contamination. It is not the source of the characteristic colour.
“A flame test can identify any unknown substance.”
Flame tests identify only certain metal ions and are qualitative. They cannot identify every substance.
“The colour of the solution predicts the flame colour.”
Lithium, sodium, potassium and calcium salt solutions used here are normally colourless. The characteristic colour appears when the sample is heated in the flame.
Can mixtures of metal ions still be identified using flame tests?
Compare pure samples with mixtures and evaluate why visual flame tests become less reliable when more than one metal ion is present.
The principle of characteristic atomic emission is used in flame emission spectroscopy and related instrumental techniques.
Before students begin, demonstrate:
During the practical, observe whether students can:
| Activity | Suggested time |
|---|---|
| Introduction and safety briefing | 7 min |
| Teacher demonstration | 8 min |
| Known standards and unknown practical | 27 min |
| Results discussion | 8 min |
| Evaluation and plenary | 7 min |
| Cleanup and shutdown | 3 min |
Overall risk level: Low. This practical presents a low level of risk when standard laboratory procedures are followed. The level of risk depends on concentrations, quantities, cleaning method, class organisation and local control measures. This table is supporting information and does not replace the school's own risk assessment.
| Hazard | Risk | Control measures |
|---|---|---|
| Bunsen burner | Burns | Tie hair back and use the yellow safety flame when not heating. |
| Dilute hydrochloric acid | Irritant | Wear eye protection and wash splashes immediately. |
| Hot wire loop | Burns | Allow the loop to cool before touching or placing it in liquid. |
| Glassware | Cuts | Handle carefully and report breakages immediately. |
| Metal salt solutions | Low hazard | Avoid ingestion or skin contact and wash hands afterwards. |
Waste and cleanup: dispose of residues using the approved local route, turn off the gas when finished, allow hot equipment to cool and wash hands after the practical.
| Question | Answer |
|---|---|
| Why do metal ions produce coloured flames? | Heating transfers energy to electrons in metal-containing particles. When the electrons return to lower energy levels, light is emitted at characteristic wavelengths. |
| Which metal ion gives a lilac flame? | Potassium. |
| Why is hydrochloric acid used? | To remove contamination from the wire loop before another sample is tested. |
| Why should the wire be cleaned between tests? | To avoid mixing flame colours. |
| Which flame is used for flame tests? | A stable blue flame is used for the observation. The yellow safety flame is used for lighting and standby. |
| Why are flame tests only qualitative? | They identify substances by colour but do not measure how much is present. |
Do not simply write that electrons “lose energy”.
State that heating excites electrons to higher energy levels and that energy is emitted as light at characteristic wavelengths when the electrons return to lower energy levels.
Sodium produces an intense yellow emission and contamination can mask weaker flame colours, particularly potassium's lilac flame.
A hot loop can cause contamination or splashing and may damage glassware. Allow it to cool before placing it into the cleaning acid or sample.
No. It provides supporting qualitative evidence. Mixtures, contamination, similar colours and low concentrations can make the result uncertain.
Compare unknowns with known standards under the same conditions or use a spectroscope or instrumental emission method to separate and measure wavelengths.
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This guide was written and reviewed by Better Equipped's technical team and further reviewed by former A Level Science Teachers. Our technical team draw on experience supplying practical science equipment to schools, colleges, laboratories and science departments throughout the UK. They include ex-school laboratory technicians and are here to support schools, colleges and laboratories. If you have feedback on this guide, we'd love to here it so please contact us. Don't forget we will be regularly updating our guides and resources on our Better-Resources Hub. If you would like us to cover a particular subject matter in these guides or have some top tips you'd like to share then again we'd love to hear from you.
Last reviewed and updated: August 2026
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