Activity 1.2 - Observation and explanation of filters

• To observe carefully and describe observations
• To use models
• To distinguish alternative (models)

• Coffee filter, empty tea bags as filters, different mixture such as tea, coffee, orange juice, mud in water…
• Pictures of particle models of different sizes

Start by showing the class the coffee filter paper and asking them what they think it is or what it can do. Ask the students why they think the coffee granules do not pass through the filter paper but the water can? Why has the water in the cup now turned brown? Ask the students to discuss whether the sieve from the previous activity could be used to make coffee.

Students carry out tests on the mixtures provided and work out which can be separated by filtration and which can’t and why.

• Why do mud, coffee granules, … do not pass through the filter paper but the water can?
• How could you use the models in the picture to explain your observation?
• What is the difference between tea and mud in water?