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

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

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 mass. With icons to indicate the conceptual level/s of each question.

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Learning objectives

Recognise that the same mass of different substances will contain a different number of atoms because different atoms have different masses.
Connect the relative mass of atoms with the relative mass of a given number of the same atoms.
Relate the mass of one mole to the mass of a given number of moles.
Use a mathematical formula to calculate mass from the number of moles and mass of one mole.
Use a mathematical formula to calculate the number of moles from mass and mass of one mole.

How to use this resource

This resource aims to develop learners’ understanding of the relationship between the mass of one mole, the number of moles and mass of a substance. The questions encourage learners to think at the sub-microscopic level about how the mass of different atoms relates to the mass of one mole of these atoms. 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 gold Johnstone’s triangle worksheet which guides learners to explore different ways to represent and describe the mass of gold at a macroscopic, sub-microscopic and symbolic level.

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 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 circulate examples of substances in the classroom, run a class practical of a chemical reaction or show a teacher demonstration of properties.

Give learners physical models to use and manipulate, such as a Molymod kits or counters.

Additional support may be needed for any learners still lacking in confidence in the required symbolic representation, for example by sharing and explaining a diagram or a simulation that can show movement of the particles.

Answers and guidance

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

Question one helps develop learners’ understanding of the idea that the same mass of different substances (macroscopic understanding) will contain different numbers of atoms (sub-microscopic understanding). This question assumes prior familiarity with the idea that atoms of different elements have different masses. The question starts using the example of coins so that initially learners can think using a visible example (macroscopic understanding).

The second question develops understanding of the connection between the relative mass of individual atoms (sub-microscopic understanding) and the relative mass of a given number of those atoms (macroscopic understanding). For example, if one atom has two times the mass of another, then 1000 atoms of those other atoms will have two times the mass of 1000 of the first type of atom.

Question three supports learners to develop understanding of the relationship between one mole as 6.02 x 10²³ atoms (sub-microscopic understanding) and the mass of a mole as the RAM in grams (macroscopic understanding).

In question four, learners develop understanding of the mathematical formula (symbolic understanding) that expresses the relationship between mass (macroscopic understanding), mass of one mole and number of moles of atoms (sub-microscopic understanding).

The final question develops learners’ understanding of a different arrangement of the mathematical formula (symbolic understanding) that expresses the relationship between number of moles (sub-microscopic understanding) and the mass (macroscopic understanding) and mass of one mole. The mathematical skill of rearranging the formula is not a focus for this resource. For that reason, the rearranged formula is provided at the start of the question.