Moles and volume | Developing understanding | 14–16 years | Resource

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Support your learners to develop mental models and deepen their understanding of moles and volume

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 moles and volume. With icons to indicate the conceptual level/s of each question.

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Learning objectives

Use the particle model to explain the compressibility of gases.
Recognise that an equal volume of any gas (at the same temperature and pressure) contains the same number of molecules (or atoms if a noble gas).
Recognise that one mole of a gaseous substance occupies 24 dm³at room temperature and pressure.
Calculate the volume occupied by a given number of moles of a gas.
Calculate the number of moles of a gas in a given volume.

How to use this resource

This resource aims to develop learners’ understanding of the idea that equal volumes of gases contain an equal number of molecules (or atoms if noble gases). The questions encourage learners to think about the relationship between volume (the macroscopic level) and the number of moles of molecules (the sub-microscopic level). 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 Moles of xenon Johnstone’s triangle worksheet, which guides learners to convert units of measurment and calculate the moles of xenon.

Support

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

It is useful for learners to observe macroscopic properties first-hand. You could show an example of a specified volume of gaseous substance in the classroom (e.g. in a sealed gas jar).

Additional support may be needed for any learners still lacking in confidence in the required symbolic representation. Examples include sharing and explaining a digital simulation that can show the arrangement and movement of the atoms or molecules of a substance in the gas state.

Answers and guidance

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

Question one develops learners’ understanding of the particle model for the gas state (sub-microscopic understanding) and how it may be used to explain the compressibility of gases (macroscopic understanding). This question assumes familiarity with the meaning of the terms atom and molecule.

Question two develops learners’ understanding of the idea that there are an equal number of molecules (sub-microscopic understanding) in an equal volume of any gas (macroscopic understanding). This is true at the same temperature and pressure and for any gas that is made up of molecules. The number of molecules will be equal to the number of atoms of a noble gas (which are made up of individual atoms).

Question three develops learners’ understanding of the volume (macroscopic understanding) occupied by one mole (sub-microscopic understanding) of any gas. It then supports learners to connect the number of moles of a gas with the volume that will be occupied at room temperature and pressure. This question assumes familiarity with the idea that one mole of a gas is made up of 6.02 x 10²³ molecules (or atoms if a noble gas). The question provides the information that 1 dm³ is equal to 1000 cm³ but assumes that learners have met dm³ before.

Question four develops learners’ understanding of how to connect the number of moles of a gas (sub-microscopic understanding) with the volume this occupies in dm³ (macroscopic understanding). This question uses a diagram to support learners in developing their understanding of the meaning of the mathematical formula volume = volume of one mole x number of moles. If appropriate learners could be taught that the volume of one mole is called the molar gas volume.

Question five develops learners’ understanding of how to determine the number of moles of a gas (sub-microscopic understanding) in a given volume (macroscopic understanding). This question uses a diagram to support learners in developing their understanding of the mathematical formula needed to calculate the number of moles from the volume and volume of one mole of a gas.