Monday, December 10, 2018

Cough Syrup: Investigating viscosity

Full details of the activity can be found in the free CIEC resource Cough Syrup which can be down loaded from

he activities in this resource look at the way a new cough syrup can be developed. Children work to identify the best conditions for growing micro-organisms to produce the active ingredient in the medicine, the best way to collect it, and the ideal consistency for the syrup. Economic and commercial factors are also considered. The activity described here invites children to investigate the effect of altering the ratios of specific ingredients on the viscosity of the resulting syrups. The aim is to find the best consistency for a cough medicine.

The Activity: Viscosity Testing

  • Activity sheet 5 (1 per child, optional)
  • 50 ml liquid glucose (available from most supermarkets or pharmacists)
  • 50 ml glycerine
  • 50 ml water
  • 20 ml measuring cylinder                                                                  
  • Small containers                                                                                           
  • Plastic spoons or stirrers
  • Measuring spoons
  • Pipettes
  • Blank sticky labels

  For the viscosity testing (depending on the test chosen)
  • 3-4 marbles
  • 1 plastic funnel
  • 1 stop clock
  • 1 30 cm length of dowel marked in centimetres
  • 1 30 x 20 cm board (or other smooth surface)

  • Begin the lesson by discussing the meaning of ‘viscosity’ with the children and explain that it is the scientific term used to describe the ‘runniness’ of a liquid. Encourage discussion about how runny a medicine would need to be, based on the children’s own experience. 
  • Show children the three ingredients that could be used to produce a syrup to carry the active ingredient in the medicine they are producing: liquid glucose, glycerine and water.
  • Next, ask the children to explain why, in a commercial environment, it is vital that a recipe is systematically recorded and reproduced so that it is identical each time? Is it important to accurately measure and record the amounts of the liquids used?  How can we ensure that the runniness is the same.
  • Ask the children how they are going to measure the viscosity of the cough syrup samples they make. Show the children the equipment listed above and get them to work in groups to think which items could be used to test viscosity (e.g. timing a marble sinking through liquid).
  • Once they have decided on a way to test viscosity the children can now begin their investigation. Encourage them to use different proportions, combinations and ratios of liquids (a total of 50 ml of any of the liquids combined is enough to obtain results).  Once a sample has been tested and recorded it can be changed to dilute or thicken and then retested provided the changes are recorded.
  • Ask the children to explain results, which combination do you think would make the best cough mixture?   Explain your conclusion. 
  • Ask the children to think about whether their tests were fair, their results reliable and whether there are any improvements that they could make to their tests.

  • Link this activity to the subject of ratio in maths.
  • Discuss the use of glucose in the recipe and the fact that sugar in medicines and food stuffs is bad for our health.

Health and Safety
  • Remind the children not to drink their samples.

  • planning different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary
  • Making measurements, using a range of scientific equipment, with increasing accuracy and precision, taking repeat readings when appropriate
  • Use observations, measurements or other data to draw conclusions

Subject Knowledge

Learning Objectives
  • Know that changes occur when materials are mixed