AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Lithium, sodium, potassium, calcium and copper compounds produce…
Full specification wording
Flame tests: Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests: lithium compounds result in a crimson flame sodium compounds result in a yellow flame potassium compounds result in a lilac flame calcium compounds result in an orange-red flame copper compounds result in a green flame.
Each of these five metal cations gives a characteristic flame colour when its compound is heated in a flame test.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Each of these five metal cations gives a characteristic flame colour when its compound is heated in a flame test. Lithium compounds give a crimson flame, sodium compounds a yellow flame, potassium compounds a lilac flame, calcium compounds an orange-red flame and copper compounds a green flame. To observe them, clean a nichrome or platinum wire in concentrated hydrochloric acid, heat it until the flame is colourless, dip it in the sample and hold it in the hot part of a non-luminous flame. The colour comes from light emitted by excited metal ions as they return to lower energy levels. Sodium yellow is intense and easily masks other colours, so careful cleaning and viewing through a blue glass can help when potassium is suspected.
What earns the marks
- Recalls the flame colour for each cation: lithium crimson, sodium yellow, potassium lilac, calcium orange-red and copper green.
- Describes the procedure of cleaning the wire, dipping it in the sample and holding it in a non-luminous flame.
- Explains that the colour is characteristic of the metal cation present in the compound.
- Uses the observed colour to identify an unknown cation by comparison with the known colours.
- Recognises that sodium yellow is intense and can mask other flame colours.
- States that the test is qualitative and does not measure the amount of the cation.
Common mistakes and how to put them right
Mixing up potassium lilac with lithium crimson.
Put it right: The error is swapping two similar-looking colours, and the correction is to learn the pairs as potassium lilac and lithium crimson.
Calling the sodium flame orange or golden.
Put it right: The error is an imprecise colour name, and the correction is to use the accepted term yellow.
Describing copper as blue-green or calcium as red.
Put it right: The error is using non-standard colour names, and the correction is to use green for copper and orange-red for calcium.
Exam tips
- Learn the five colour-cation pairs as a table and recall them without prompts.
- When identifying an unknown, state the colour observed and then name the cation it indicates.
- Mention that a blue glass may be used to filter out intense sodium yellow when testing for potassium.
Try the lesson
The start of the Flame tests: Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests: lithium compounds result in a crimson flame sodium compounds result in a yellow flame potassium compounds result in a lilac flame calcium compounds result in an orange-red flame copper compounds result in a green flame. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following metal ions produces a green flame when tested in a Bunsen burner flame?
Listen
Each of these five metal cations gives a characteristic flame colour when its compound is heated in a flame test. Lithium compounds give a crimson flame, sodium compounds a yellow flame, potassium compounds a lilac flame, calcium compounds an orange-red flame and copper compounds a green flame. To observe them, clean a nichrome or platinum wire in concentrated hydrochloric acid, heat it until the flame is colourless, dip it in the sample and hold it in the hot part of a non-luminous flame. The colour comes from light emitted by excited metal ions as they return to lower energy levels. Sodium yellow is intense and easily masks other colours, so careful cleaning and viewing through a blue glass can help when potassium is suspected. A strong answer earns marks for these points. Recalls the flame colour for each cation: lithium crimson, sodium yellow, potassium lilac, calcium orange-red and copper green. Describes the procedure of cleaning the wire, dipping it in the sample and holding it in a non-luminous flame. Explains that the colour is characteristic of the metal cation present in the compound. Uses the observed colour to identify an unknown cation by comparison with the known colours. Exam tip: Learn the five colour-cation pairs as a table and recall them without prompts.
See it
Key words
Say what each word means before you turn the card.
Characteristic flame colours of metal cations
Try answering aloud or in your head before turning the card.
Qualitative identification by comparison with standards
Try answering aloud or in your head before turning the card.
Emission of light by excited ions
Try answering aloud or in your head before turning the card.
Interference between overlapping test results
Try answering aloud or in your head before turning the card.
See every definition
- Characteristic flame colours of metal cations
- Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests, and the colour is characteristic of the metal cation present in the compound.
- Qualitative identification by comparison with standards
- The observed colour is used to identify an unknown cation by comparison with the known colours, and the test is qualitative and does not measure the amount of the cation.
- Emission of light by excited ions
- The colour comes from light emitted by excited metal ions as they return to lower energy levels.
- Interference between overlapping test results
- Sodium yellow is intense and easily masks other colours, so careful cleaning and viewing through a blue glass can help when potassium is suspected.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Flame tests: Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests: lithium compounds result in a crimson flame sodium compounds result in a yellow flame potassium compounds result in a lilac flame calcium compounds result in an orange-red flame copper compounds result in a green flame.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge