Developing understanding of concentration and mass

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

Learning objectives

1. Connect the mass of solute dissolved in equal volumes of water to the relative concentrations of the solutions formed.
2. Interpret and evaluate particle diagrams of more and less concentrated solutions.
3. Determine the concentration of a solution in units of g/dm³.
4. Calculate the concentration of a solution in units of g/dm³ from the mass of solute in g and the volume of water in cm³.
5. Calculate the mass of solute in a solution of given volume and concentration.

How to use this resource

This resource aims to develop learners’ qualitative and quantitative understanding of concentration; helping learners’ to develop mental models of solutions of different concentrations expressed in g/dm³. In this concentration and mass worksheet, learners are encouraged to think about concentration both observationally and quantitively, as well as how this can be represented using particle diagrams. As a result, learners should develop more secure mental models to support their understanding of 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 Concentration of sodium hydroxide Johnstone’s triangle worksheet which guides learners to explore difference ways to represent and describe sodium hyroxide (NaOH) solution 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 one mole of a substance 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™ kit 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.