Filtration | Developing understanding | 11–14 years | Resource

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Filtration is a separation technique which allows undissolved materials to be separated according to particle size

Developing understanding is a series of resources that encourages learners to connect their thinking at the macroscopic, sub-microscopic and symbolic levels.

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A ramped worksheet to help learners develop their mental models of filtration. With icons to indicate the conceptual level/s of each question.

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Learning objectives

Recall key vocabulary relating to the process of filtration.
Recognise that kitchen equipment can separate different foods from water due to the relative size of the holes in the equipment and the smallest pieces of the food.
Explain why mixtures of some substances with water can be separated using filter paper and why some substances cannot.
Identify whether a mixture of an unfamiliar substance with water can be separated, based on information on whether that substance is soluble or insoluble.
Name the residue and filtrate when a given mixture is poured through filter paper.
Recognise that filtration cannot remove dissolved impurities.

How to use this resource

This resource aims to develop learners’ understanding of filtration. The questions encourage learners to think about the relative size of the holes in filter paper compared with visible small pieces of undissolved material and invisible particles. As a result, learners should develop more secure mental models to support their thinking about this topic.

When to use? Use after initial teaching or discussion of this topic to develop ideas further. You can also use as a revision activity.
Group size? Suitable for independent work either in class or at home. Or use the questions for group or class discussions.
How long? 15–30 mins

Johnstone’s triangle

Johnstone’s triangle is a model of the three different conceptual levels in chemistry: macroscopic, symbolic and sub-microscopic. You can use Johnstone’s triangle to build a secure understanding of chemical ideas for your learners.

Introduce learners to Johnstone’s triangle with our Filtering muddy water Johnstone’s triangle worksheet which guides learners to think about separating mixtures of dissolved and undissolved substances in the context of filtering muddy mineral water.

Johnstone’s triangle and this resource

The icons in the margin indicate which level of understanding each question is developing to help prompt learners in their thinking.

Macroscopic: what we can see. Think about the properties that we can observe, measure and record.
Sub-microscopic: smaller than we can see. Think about the particle or atomic level.
Symbolic: representations. Think about how we represent chemical ideas including symbols and diagrams.

The levels are interrelated, for example, learners need visual representation of the sub-microscopic in order to develop mental models of the particle or atomic level. Our approach has been to apply icons to questions based on what the learners should be thinking about.

Questions may be marked with two or all three icons, indicating that learners will be thinking at more than one level. However, individual parts of the question may require learners to think about only one or two specific levels at a time.

Support

This worksheet is ramped so that the earlier questions are more accessible. The activity becomes more challenging in the later questions. You can give extra explanations for the more challenging questions. If completing this worksheet as an in-class activity, it is best to pause and check understanding at intervals, as often one question builds on the previous one.

Answers and guidance

There are five multi-part questions in the student worksheet. The answers can be found in the teacher notes.

The first question develops learners’ understanding of filtration in connection with a real-life example (macroscopic understanding).

The second question develops learners’ understanding of how filtration works by considering the relative size of holes in kitchen separation equipment compared with the size of pieces that will or will not pass through (macroscopic understanding). The question also includes the idea that water is made up of particles which are smaller than the holes in all the examples, including filter paper (sub-microscopic understanding).

The third question develops learners’ understanding of the difference in size of observable specks of materials such as mud compared with particles of water or dissolved substances (macroscopic and sub-microscopic understanding). The question then relates these sizes to the size of holes in filter paper to support student understanding of how filtering works as a separation technique. Please note that the word ‘particle’ has been specifically avoided when referring to tiny pieces of undissolved substances such as powdered chalk. Whilst this is common in everyday language there is a risk of confusing students as in chemistry particle is a word used to refer to atoms or molecules.

The fourth question develops learners’ understanding of typical laboratory equipment used for filtering and the expected observations following the filtering of mixtures of soluble or insoluble substances with water (macroscopic understanding).

The final question develops learners’ understanding of filtration by considering more deeply what passes through a filter when muddy lake water is filtered (macroscopic understanding). Learners also recap that water contains dissolved minerals (sub-microscopic understanding). The idea of microorganisms may also be included to support an understanding of scale.