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GCSE Chemistry Tutor Booster. Chemical Tests.

Using fireworks to boost your GCSE science knowledge of chemical analysis.

· GCSE Science Notes

It's that time of year again. Firework night, 5th November. So, here is a topical GCSE science tutor booster on cation and gas tests.

Flame tests (cation tests) can partly explain the colours seen in fire works and gas tests because gas is involved in the explosions.

The red, orange, yellow, green, blue and purple colors exploding in the night sky during a fireworks display are created by the use of metal salts. Remember, in chemistry ‘salt’ refers to any compound that contains metal and non-metal atoms. Some of these compounds produce intense colors when they are burned, which makes them ideal for fireworks.

Metal salts commonly used in firework displays include: strontium carbonate (red fireworks), calcium chloride (orange fireworks), sodium nitrate (yellow fireworks), barium chloride (green fireworks) and copper chloride (blue fireworks). Purple fireworks are typically produced by use of a mixture of strontium (red) and copper (blue) compounds.

The metal part of the salt are cations. In GCSE science (chemistry) you would a studied cations and how to identify the cations in unknown sustances using the flame test.


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A flame test is used to detect the presence of an  metal ion. The metal ion will turn a blue Bunsen burner flame a different colour. 

A clean, moist flame test wire is dipped into the substance to be tested and then put into the edge of a blue Bunsen burner flame. If a metal ion is present in that substance then the flame will turn the colour indicative of that metal ion. Below shows the flame test identifying the presence of copper ion in a substance.


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Here is a flame test colour chart:


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After a firework is ignited, a lift charge propels it into the sky. That’s just explosive black powder in a confined space that, when lit, causes a fast increase of heat and gas that can send a firework as high as 1,000 feet (300 meters) into the air.

Fireworks are combustion reactions. They are extremely rapid, exothermic reactions that require oxygen. So, here goes to the next part of this GCSE science booster tutor - identifying gases.

First, oxygen. A glowing splint relights in a test tube of oxygen, as shown below.


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Next, hydrogen. A lighted splint makes a popping sound in a test tube of hydrogen.


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A lighted splint in a test tube of carbon dioxide will go out. However, this happens with other gases too so the best test is with limewater. Carbon dioxide will turn limewater from a clear solution to cloudy.


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Ammonia gas has a characteristic choking smell and will also turn damp red litmus paper or universal indicator paper blue. Ammonia gas also forms a white smoke of ammonium chloride when hydrogen chloride from concentrated hydrochloric acid is held near.

Chlorine gas has a characteristic choking smell and will also turn damp blue litmus paper red and then bleach it white. 

Chlorine gas also turns damp starch-iodide paper blue-black.