Predict what will happen to the volume of materials when they are added together… then observe and notes your findings
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.
- Eye protection
- Stirring rod
- Measuring cylinders, 100 cm3, x2
- Sodium chloride
- Dried peas
Health, safety and technical notes
- Read our standard health and safety guidance.
- Always wear eye protection.
- Ethanol is flammable, see CLEAPSS Hazcard HC040a.
- Add approximately 25 cm3 of dried peas and 25 cm3 of sand to separate measuring cylinders. Accurately measure and record the volumes.
- The contents of one cylinder is added to the other and shaken until the two substances are mixed together.
- Place the measuring cylinder on the bench and gently shake from side to side to allow the mixture to settle.
- Read the combined volume.
- Add approximately 25 cm3 of ethanol and 25 cm3 of water to separate measuring cylinders. Accurately measure and record the volumes.
- 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.
- Read the combined volume.
- To the measuring cylinder, add approximately 75 cm3 of water. Accurately measure and record the volume.
- 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.
- The volume reading on the side of the cylinder should again be recorded.
What to record
|Volume of peas/ cm3||Volume of sand/ cm3||combined volume/ cm3|
|Volume of alcohol/ cm3||Volume of water/ cm3||Combined volume/ cm3|
|Initial volume of water/ cm3||Final volume of salt solution/ cm3|
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.
- What is the similarity between the first two activities?
- What is an explanation for the result in the last activity?
- Both activities involve the mixing of particles, combined volumes are less than the sum of the parts.
- Salt particles mix between the water particles is a simple explanation.
This practical is part of our Classic chemistry experiments collection.