Produce a spectacular fireball by sprinkling milk powder over a flame, and witness how an increased surface area can also increase reaction rates.
A pile of dried milk powder will not ignite even if a roaring Bunsen flame is played onto it. However, if the powder is sprinkled onto a flame, a spectacular fireball is produced which demonstrates the increased reaction rate by increasing surface area.
This practical should take 5 minutes.
- Eye protection
- Bunsen burner
- Heatproof mats
- Metre rule
- Wooden splints
- Stand with bosses and clamps, x 2
- Wooden cubes (Tillich’s bricks), 1 cm × 1 cm × 1 cm, x 8
- Powdered milk
Health, safety and technical notes
- Read our standard health and safety guidance.
- Both demonstrator and audience should wear eye protection.
- Your employer’s risk assessment should be consulted before carrying out this activity.
- Take care to ensure that no lampshades, ceiling hangings or any other flammable materials are within reach of the flames.
- A preliminary fire-alarm check is advised
- Please advise pupils not repeat this experiment at home.
Before the demonstration
- Attach a wooden splint to the end of a metre rule using Sellotape so that most of the splint projects beyond the end of the rule.
- Protect the bench with heatproof mats – enough to cover approximately 1 m2 of bench.
- Place a little milk powder in a pile on a heatproof mat or metal tray.
- The pile should be compact and form a cone about 1 cm high and 2 cm in diameter.
- Now aim a roaring Bunsen flame at the pile of powder, using the hottest part of the flame just beyond the blue cone.
- The milk powder will char, but will not continue to burn once the flame is removed.
- Now use the two stands and clamps to support the metre rule horizontally about 5 - 10 cm above the bench so that the spill is above the heatproof mats.
- Light the spill.
- From a height of about ½ m, pour milk powder onto the lighted spill. A small fireball will form as the powder comes into contact with the flame.
- It is possible for large fireballs to reach the ceiling, so this may require protection
Take care to transfer the milk powder from the full container to a smaller vessel first to avoid setting the entire tin alight.
The higher the powder is sprinkled from, the bigger the fireball, so it is wise to experiment starting from a small height until you can produce a fireball that is large enough to be spectacular but small enough for you to be comfortable with.
There will be some ‘fallout’ of burnt powder, so have a brush or vacuum cleaner ready to clear up the bench.
Some students may have difficulty with the idea that a powder has a greater total surface are than the corresponding solid, since each speck of a powder clearly has a very small surface area.
The following model may help.
- Use eight Tillich’s bricks to make a 2 × 2 × 2 cube.
- Find the surface area by counting the exposed squares – it will be 24 cm2.
- Now dismantle the cube into eight bricks and again find the total surface area of the bricks – it will be 48 cm2.
- Alternatively, chalk over the outside of the 2 × 2 × 2 cube and then dismantle it into the eight smaller cubes.
- Each will have three of its six sides chalked and three newly-exposed sides
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This practical is part of our Classic Chemistry Demonstrations collection.