Developing understanding of yield

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

Learning objectives

1. Recognise that actual yield may be less than the yield that could theoretically be produced and that this can be shown quantitively by calculating the percentage yield. 
2. Calculate the theoretical yield for a given reaction from the mass of a reactant and the balanced chemical equation.
3. Determine the location of product ions following the separation of an insoluble product.
4. Suggest a reason for a calculated percentage yield that is less than 100%.

How to use the resources

This resource aims to develop learners’ understanding of the idea of actual and theoretical yield. The questions encourage learners to think at the sub-microscopic level about the location of ions following the separation of an insoluble product and about why actual yield may not equal the theoretical yield. 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, sub-microscopic and symbolic. 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 Yield of fertiliser worksheet, which guides learners to consider the difference between actual and theoretical yield of ammonium sulfate in the context of fertiliser.

Scaffolding

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.