Flame Tests

Purpose

Identify metal ions by the colour they produce in a flame, and connect that colour to electron behaviour.

Safety

Open flame, tied-back hair, goggles on. Nichrome loops are hot long after they stop glowing. Never point a burning splint at anyone.

Background

Heat gives an electron enough energy to jump to a higher shell. It falls back almost immediately and emits the difference as light. Because each element’s shells are spaced differently, each emits its own colours.

$$E_{\text{photon}}=E_{\text{high}}-E_{\text{low}}$$

Procedure

1. Clean the loop in acid, then in the flame, until it adds no colour.
2. Dip in the first solution and hold in the hottest part of the flame.
3. Record the colour immediately — the good ones last under a second.
4. Clean thoroughly between samples.

Data

Solution	Metal ion	Flame colour	Confidence
Lithium chloride	$\mathrm{Li}{}^{+}$
Sodium chloride	$\mathrm{Na}{}^{+}$
Potassium chloride	$\mathrm{K}{}^{+}$
Calcium chloride	$\mathrm{Ca}{}^{2+}$
Copper(II) chloride	$\mathrm{Cu}{}^{2+}$
Unknown	?

Analysis

1. Identify the unknown. State exactly which observation decided it.
2. Every solution above is a chloride. Why does that matter for the conclusion?
3. Sodium contaminates everything — a trace turns any flame yellow-orange. How did you guard against that, and how confident are you?

Where else you have seen this

Fireworks are flame tests with a budget. Strontium for red, barium for green, copper for blue. Astronomers use the same principle in reverse to determine what distant stars are made of — see the evidence about the universe’s origin.

Hand in

• Data table
• Identification of the unknown with reasoning
• Answers to analysis questions

Curriculum connection

A1.2

apply a scientific experimentation process and associated skills to conduct investigations, making connections between their observations and findings and the scientific concepts they are learning

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C2.2

research the role of experimental evidence in the development of various atomic models, and compare and contrast different models of the atom

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C2.5

investigate the physical and chemical properties of elements, and use their findings to relate these properties to the organization of the periodic table, classify elements, and identify patterns in the periodic table

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