Experiments with particles

When materials are added together, they may acquire new properties. When a solid and a liquid are mixed, the solid may or may not dissolve. When two liquids are mixed they may become one liquid or stay separate. These experiments provide an opportunity to predict and then observe what happens.

This experiment should take 45 minutes. 

Equipment

Apparatus

• Eye protection
• Stirring rod
• Measuring cylinders, 100 cm³, x2 
• Spatula

Chemicals

• Sodium chloride
• Water
• Sand
• Dried peas
• Ethanol

Health, safety and technical notes

• Read our standard health and safety guidance.
• Always wear eye protection.
• Ethanol is flammable, see CLEAPSS Hazcard HC040a.

Procedure

Activity 1 

1. Add approximately 25 cm³ of dried peas and 25 cm³ of sand to separate measuring cylinders. Accurately measure and record the volumes.
2. The contents of one cylinder is added to the other and shaken until the two substances are mixed together. 
3. Place the measuring cylinder on the bench and gently shake from side to side to allow the mixture to settle. 
4. Read the combined volume.

Activity 2

1. Add approximately 25 cm³ of ethanol and 25 cm³ of water to separate measuring cylinders. Accurately measure and record the volumes.
2. The contents of one cylinder is added to the other and shaken from side to side for 15–30 seconds until the two substances are mixed together, and then left to stand for one minute.
3. Read the combined volume.

Activity 3

1. To the measuring cylinder, add approximately 75 cm³ of water. Accurately measure and record the volume.
2. Spatulas of salt should then be added one at a time until the salt begins to be left at the bottom of the cylinder, despite continued stirring.
3. The volume reading on the side of the cylinder should again be recorded.

What to record

Activity 1

Volume of peas/ cm3

Volume of sand/ cm3

combined volume/ cm3

Activity 2

Volume of alcohol/ cm3

Volume of water/ cm3

Combined volume/ cm3

Activity 3

Initial volume of water/ cm3

Final volume of salt solution/ cm3

Notes

Ensure that the students understand what is meant by prediction.

Students should be encouraged to suggest explanations for their results, even if the inferences seem not to support their predictions – eg 25 cm³ peas + 25 cm³ sand = 46 cm³ total volume.

A student may feel that water and alcohol are continuous materials, with the heavier one resting on the other – therefore squashing the lighter one.

The effect would be to have a lower total volume.

Students may need reminding not to try and measure 25 cm³ accurately but to pour approximately, then take an accurate measurement.

Questions

1. What is the similarity between the first two activities?
2. What is an explanation for the result in the last activity?

Answers

1. Both activities involve the mixing of particles, combined volumes are less than the sum of the parts.
2. Salt particles mix between the water particles is a simple explanation.