Quick answer: The particle model says that all matter is made of tiny particles that are always moving. This grade 7 science lab on particle model gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
Does hot water make dye spread faster than cold water? In this lab you add a drop of food colouring to four cups at different temperatures and time how long it takes to colour the whole cup. You then link the results to the speed of the water particles.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-PS1-1, MS-PS1-4
Aim
To find out how the temperature of water affects how quickly a drop of food colouring spreads through it.
Equipment
- 4 identical clear plastic cups
- Cold, room-temperature and hot tap water, ice
- Thermometer
- Food colouring and a dropper
- Stopwatch or phone timer
- Measuring jug (150 mL)
- White paper
Safety
Hot water can scald. Use water no hotter than 60 °C, ask an adult to pour it, and wipe up spills straight away. Food colouring stains skin and clothes, so wear an apron.
Method
- Place the cups on white paper and label them 1 to 4.
- Prepare 150 mL of water at about 5 °C, 20 °C, 40 °C and 60 °C, one for each cup. Check each with the thermometer.
- Wait 30 seconds so the water is still.
- Add one drop of colouring at the water surface in cup 1 and start the timer at the same moment.
- Stop the timer when the colour looks even throughout the cup.
- Repeat for cups 2, 3 and 4 and record the times.
Results
A class in Kampala obtained these times:
| Cup | Temperature (°C) | Time to spread evenly (s) |
|---|---|---|
| 1 | 5 | 540 |
| 2 | 20 | 300 |
| 3 | 40 | 170 |
| 4 | 60 | 95 |
Analysis questions
Question 1 Identify the variables
Identify the independent variable, the dependent variable and two control variables.Question 2 Describe the pattern
Describe how the time changes as the temperature increases.Question 3 Compare the extremes
Calculate how many times longer the colour takes to spread at 5 °C than at 60 °C.Question 4 Calculate the speeds
Assume the colour spreads across a cup width of 8.0 cm. Calculate the average spreading speed at 20 °C and at 40 °C.Question 5 Explain with particles
Explain the results using the particle model.Question 6 Judging the end point
Explain why the end point ‘looks even’ makes the results uncertain, and suggest an improvement.Question 7 Another source of error
Suggest one other source of error and say how it affects the results.
