Numeracy Activity 2 – Calculating Concentration

Calculating Concentration - Household Chemicals [Stage 5]

 * Main focus: CW3b. identify a range of compounds using their common names and chemical formulae
 * Additional outcomes and content statements:
 * CW3 Chemical reactions involve rearranging atoms to form new substances; during a chemical reaction mass is not created or destroyed
 * WS7.1 Students process data and information by
 * d. applying numerical procedures and mathematical concepts and using digital technologies, where appropriate

Activity Outline
In this lesson, students will identify chemical compounds within household products including cleaning products, food products, medications and gardening supplies. After identifying what chemicals can be found in the house, students will then calculate the concentration or mass percentage of active ingredient in these different products. This will serve to contextualise what they have learnt in CW3b, that is, that chemicals that sound like they only have application in chemistry, in fact, are of use in our day-to-day lives.

In order to perform this lesson, the teacher must bring appropriate household products to the class. These products must have an obvious and common active ingredient and also be safe for use in a high school classroom. These can include:
 * Calcium supplement tablets, paracetamol tablets


 * Household bleach


 * Methylated spirits


 * Fly spray or garden pesticide


 * Toothpaste
 * Aquarium products

Using these products, students will be taught how to find the ‘active ingredient’ on the label of the products. One product will be assigned to each group of 3 students.

Students will spend time observing the given online worksheet (see PDF) in order to identify and recognise chemical compounds found within their own homes. The sheet also shows the common name and chemical formula for each compound.

After students identify the active ingredient (including chemical formula and common name) of all products, they are to calculate what percentage of the product is active ingredient. Students will be taught in simple terms what the following may mean, and how concentration or percentage can be calculated from these measurements: Students will utilise digital scales or measuring cylinders, depending on what product they have been given.
 * w/w
 * mL/L
 * g/kg
 * ppm
 * g/L

Differentiation and Considerations

 * Students who excel at the activity may be given a product that has a concentration/percentage that is a little more complex. This may include measurements where units may have to be converted (e.g. 0.5mg/g paracetamol).
 * Students who struggle with the activity may be given a product with a more simple percentage (e.g. 950ml/L methylated spirits).
 * A task can be set at the end to create a sector graph to indicate how much of the product is active ingredient. Students who finish early can move on to complete this task. Further excelled students may put other ingredients into the sector graph.
 * For students extremely gifted in science/numeracy (e.g. accelerated students, tutored students, etc.) considering taking chemistry in the next year, the concept of moles may be introduced. Some medications (e.g. some supplements) are expressed in mol/g. This would serve as an introduction to preliminary chemistry.