Chemistry 11–12 · Year 11

Flame tests of metal ions and the line-spectrum model of energy levels

Module 1: Properties and Structure of Matter

Practical, model not builtMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Each metal ion emits its own colour because electrons drop between discrete energy levels; the emitted wavelengths are fixed for that element.

Safety card

Medium riskLearners carry it out, with a teacher supervising

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

naked flame
copper(II) chloride is harmful and irritant
lithium and strontium chlorides irritate eyes
hydrochloric acid 2 mol/L irritant if wire method used
the hydrogen discharge tube runs from a high-voltage supply and becomes hot

Controls

eye protection
hair tied back
splints go in a beaker of water after use
solutions in dropper bottles, not open beakers
wash hands
only the teacher operates the discharge tube; the supply is switched off before the tube or its holder is touched, and the tube is left to cool

Note

NSW Department of Education Chemical Safety in Schools (CSIS) package, 2021 Technical Update: Section 1.7 (risk assessment) and Volume 2 Appendix D (generic assessment advice and DoE chemical categories); record a RiskAssess (riskassess.com.au) risk assessment before the lesson and check the school's hazardous chemical register (CSIS Section 1.9) for local restrictions.

What you need

0.5 mol/L solutions (about 20 mL each) of lithium chloride, sodium chloride, potassium chloride, calcium chloride, strontium chloride and copper(II) chloride
Wooden splints soaked overnight in each solution (one set per solution, labelled), or a nichrome wire loop with 2 mol/L hydrochloric acid for cleaning
Bunsen burner, heat-resistant mat
Cobalt-blue glass or a handheld diffraction grating (about 500 lines per mm) or a spectroscope
Hydrogen discharge tube and power supply (teacher use) for the line-spectrum comparison, if the school has one

How to do it

Set the Bunsen to a roaring blue flame.
Hold the tip of a soaked splint in the edge of the flame for two to three seconds and record the colour; use a fresh splint for each solution.
View a sodium flame and a potassium flame through cobalt-blue glass and record the difference.
View each flame through the diffraction grating and sketch the colours seen; if a hydrogen tube is available, view it through the grating and note the separate red, blue-green and violet lines.
Test an unknown solution provided by the teacher and identify the metal from the colour.
Run the simulation: choose the upper level n and read the wavelength of the hydrogen Balmer line; compare with the lines seen through the grating.

What you should see

Lithium gives a crimson to magenta flame, sodium an intense yellow, potassium lilac (seen clearly only through cobalt-blue glass, which removes the yellow), calcium orange-red, strontium crimson-red and copper(II) blue-green. Through the grating each flame shows discrete coloured lines or bands rather than a continuous rainbow. For hydrogen the visible Balmer lines computed from the Rydberg formula are 656.5 nm (n = 3 to 2, red), 486.3 nm (4 to 2, blue-green), 434.2 nm (5 to 2, blue-violet) and 410.3 nm (6 to 2, violet); the learner sees the red and blue-green lines readily.

What changes

What you change: metal ion in the solution
What you measure: flame colour and the lines seen through the grating
What you keep the same: flame setting
splint soaking time
distance from the flame
viewing conditions

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Flame colour comes from the anion (chlorides are used so that the metal ion alone sets the colour).
The flame colour is a mixture like paint (it is a set of discrete lines; sodium's yellow masks other colours, which is why the blue glass is needed).
Electrons spiral gradually between levels (the emission is at fixed wavelengths because the levels are discrete).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH11-8 CH11/12-3 CH11/12-4
Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-11-01 CH-11WS-03
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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