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What is in a firework?

14-16

In these two practical activities, students use party poppers and sparklers to investigate the principles behind fireworks and explore, through flame tests, what creates different colours when fireworks are set off. They work in groups to make and share their observations. The activities offer the alternative of a group experiment or demonstration for the flame test activity.

Learning objectives

Students will be able to describe:

• what is in a firework.
• what makes the different colours we see when fireworks are let off.

Sequence of activities

	Use pictures of fireworks to introduce the learning objectives. Invite students to suggest what they think might be in fireworks. Explain that they are going to do experiments to find out what is in fireworks.
	Organise students into groups of four. Give each student a copy of What is a firework?. If you prefer not to give party poppers and sparklers to every group, select students to let these off in front of the whole class, then work in groups. Explain the task and then supervise the groups as they: let off the party poppers and burn the sparklers complete the observation table, recording in each case what they saw and what they smelt and heard answer questions 1‑4 on the worksheet, agreeing answers within the group agree on a one sentence definition for a firework, for question 5 select a spokesperson to feedback their one sentence definition to the class.
	In a plenary, encourage students to listen to each group’s definition. Work towards a whole class definition. Ensure this includes key words such as:  chemical reaction, explosive, colour agent(s), fuel, chemicals.
	Decide if you wish to carry out a demonstration or run the next activity as a practical, in groups. Explain the task, to investigate what creates the colour effects in fireworks. Give each student a copy of the worksheet What is in a firework?. Sequence for group practicals Prepare samples, beforehand, of eight different solids in labelled Petri dishes, each with one or more flame test wires. Note that flame tests on barium and zinc salts should be demonstrated due to their toxicity. Demonstrate barium chloride (green) and zinc chloride (white-green) to show the technique. Supervise and support as the groups: carry out flame tests on the range of solids complete the results table provided answer questions 1 and 2 on the sheet select a spokesperson to give their answers to the class. Allow about 40 minutes for the practical work. Note, if time is short, give each group a different solid, to ensure the full range is tested, and then arrange for the results to be shared. The alternative sequence If using only teacher demonstrations: carry out flame tests on each substance give time for the students to write down the colours in the table support the groups as they answer questions 1 and 2 on the sheet ask groups to select a spokesperson to give their answers to the class. Allow about 25 minutes for the demonstration.
	Bring the students together for a plenary. Share the results from the flame tests, if a class experiment was done. Give each student a copy of the Periodic Table, or ensure one is available. Lead the discussion as the groups give their answers to the two questions. Question 1: The metallic elements in the compounds create different colours. Their ions have different structures. The structural differences between the ions cause the different colours. Question 2: Heat is needed to see the colours. Heat is used to excite electrons in the metallic elements. The excited electrons give out light energy of different wavelengths (colours) as they move within the ions. Draw out key points in the discussion. Use the Periodic Table to link the results to atomic structures and positions of elements in the Table. Pose further questions to take the key points further, depending on the level of the students. What do they notice about where the elements used in fireworks are located? Why are not all metallic elements used in fireworks?
	Collect students’ worksheets from both experiments and give written feedback reinforcing the good qualities of the points raised by the students.

Assessment for learning commentary

The fireworks context provides a vehicle for students to share thinking and to help them make the connection between properties and the Periodic Table, as well as to learn about a familiar item.

The collaboration needed in group discussions and experimental work ‑ as they listen and give feedback ‑ necessarily involves students in evaluating each other’s work. 

Questions and feedback, during the plenary, lead the students to make the appropriate connections between experimental results and chemical theory. Written feedback supports students as they develop their thinking in this area.

Resources

Props

For each student

		What is a firework?
		What makes the colours in fireworks?

• A copy of, or access to, the Periodic Table.

Equipment

For each student

• Eye protection.

What is a firework?

For each group of students

• One or more party poppers
• One or more sparklers.

For the whole group of students

• Bucket of cold water for the burnt sparklers
• Bag to collect party popper materials.

What makes the colours in fireworks?

For each group of students

• Samples of firework chemicals (see list)
• Flame test wires (these can be placed with the chemicals)
• Distilled water
• Small beaker or test-tube
• Bunsen burner
• Heatproof mat
• Pump action spray bottles, one for each chemical
• About 10 cm³ ethanol per chemical (Highly flammable).

Chemicals to test: Sodium chloride (yellow), potassium chloride (lilac), copper(II) carbonate (Harmful) (blue-green), strontium chloride (red), calcium chloride (Irritant) (red-orange), barium chloride (Toxic) (green), lithium chloride (Irritant) (red), zinc chloride (Corrosive) (white-green), magnesium chloride (no colour), iron filings (gold).

Preparation notes

Chlorides are best to use. Prepare each in a Petri dish, labelling both the top and base of the dishes to ensure these don’t get muddled. Preparing two or three of each would ensure that there is sufficient to go round a class comprising 7‑8 groups of four students. Wires should be kept with each dish. Teachers are advised to demonstrate barium and zinc salts as these are toxic/corrosive.

The water is used to help the solid stick to the wire. Very little solid is required. The edge of the Bunsen flame is the best place to put the wire. Dimming laboratory lights will help heighten the effects.

Make saturated solutions of each of the solids in ethanol where possible. Only very small quantities of the solids are required.

Place each solution in a separate spray bottle.

Label each bottle.

Set the nozzles of the bottles to give a fine spray, not a jet.

The prepared bottles can be kept for several weeks without deterioration of the plastic or solution.

Notes about the demonstration

• Darken the room.
• Set the Bunsen burner to a roaring flame.
• Spray each solution in turn into the flame. Take care not to spray towards the audience.

Safety notes

It is the responsibility of the teacher to carry out appropriate risk assessments. See the notes above.

• Eye protection should be worn.

Principal hazards

• Sparklers and party poppers
• Spraying chemicals.

Answers

What is a firework?

Questions

• The explosive lifts the streamers out of the container. The explosive is ignited when the cord is pulled.
• The solid substance reacted with oxygen in the air. Gases were made which went into the air. Iron was in the sparkler. The iron filings were heated up and also went into the air.
• The heat from the chemical reaction produced the sparks. The iron filings heated up and gave off light.
• Colour, light, lifting charge, heat and smoke.
• A firework is …an explosive mixture comprising a mixture of substances where the mixture includes fuel, a supply of oxygen and other chemicals to create effects.

What makes the colours in fireworks?

Questions

• The metallic elements have different numbers of electrons. These are affected by the heat energy in different ways, giving out light of different colours.
• Heat is used to excite the electrons.

Acknowledgements

V. Kind, Contemporary chemistry for schools and colleges. London: Royal Society of Chemistry, 2004.
T. Lister, Classic chemistry demonstrations. London: Royal Society of Chemistry, 1995.