Science at Work in Healthcare

Post – 16 Science Education Pack

Key Stage 5 Chemistry

Lesson Plan 2 – Faecal Fat Analysis

Lesson aim

To familiarise students with the use of chemical analysis in a healthcare related context, and to give students an idea of how the results can be used in diagnosis.

Lesson objectives

Students will:

  • Work in pairs to prepare a sample and carry out a titrimetric analysis.
  • Calculate the mass of fat present in a synthetic faeces sample.
  • Identify flaws in the method used and suggest improvements.
  • Appreciate how experimental procedures are used in a real-world context.
  • (Extension) Research alternative methods for carrying out faecal fat analysis.

Lesson outcomes

By the end of the lesson:

  • All students will be able to describe and carry out an experimental procedure to analyse the fat content of a synthetic faeces sample.
  • Most students will be able tocalculate the amount of fat present in the sample provided.
  • Some students will be able tojustify improvements to the experimental procedure and suggest alternative methods for analysing fat content of samples.

Specification Links

Board / Unit / Spec.
AQA / 1 / 3.1.2 (reactions and equations)
3 / Practical Skills
4 / 3.4.5 (carboxylic acids and esters)
6 / Practical Skills
Edexcel / 1 / 1.3 (reactions and equations)
3 / Laboratory Skills
4 / 4.8 (carboxylic acids and derivatives)
6 / Laboratory Skills
OCR A / F321 / 1.1.2 (moles and equations)
F323 / Practical Skills
F324 / 4.1.3 (carboxylic acids and esters)
F326 / Practical Skills
OCR B (Salters) / F331 / (formulae, equations and amount of substance)
F333 / Chemistry in Practice
F334 / (organic functional groups and organic reactions)

Materials and Equipment

Per student

  • Resource Sheet 2.4 – What is Steatorrhoea?

Per pair of students

  • 1 pre-prepared synthetic faeces sample (see Technician Notes)
  • 250 cm3beaker
  • 250 cm3 conical flask
  • Access to distilled water
  • Glass rod
  • Pasteur pipette (plastic) with the tapered end removed (this gives a bigger opening)
  • 10cm3 transfer (volumetric) pipette and filler
  • 50 cm3 burette
  • Resource Sheet 2.1 – Analysing Faecal Fat
  • Resource Sheet 2.2 – Faecal Fat Results
  • Resource Sheet 2.3 – Calculation Help Sheet

For the whole class

  • Hot water bath (at 90 °C) or steam bath (Bunsen flames are not suitable!)
  • 3% potassium hydroxide solution in ethanol (each group needs 50 cm3).
  • 33% HCl solution (each group needs 15 cm3).
  • mol dm-3 NaOH in ethanol (each group needs 50 cm3 for their burette. You may wish to collect unused reagent for disposal).
  • Large bowl of ice-water.
  • Dropper bottle of 1% ethanolic phenolphthalein.

Lesson structure

Intro activity:

  • Ask the students ‘What steps lead to the production of faeces in the body?’ or a similar open question. This is something that will have been covered in previous Key Stages.
  • The key point students need to appreciate is that as food is digested, nutrients are absorbed in the small intestine and the indigestible waste passes through the large intestine as faeces.
  • Follow up with discussion about the nutrients (particularly carbohydrates, proteins and fats) and how they are digested (e.g. chemical breakdown of fats by enzymes to fatty acids followed by absorption). Ask the students ‘Why might a patient have a high fat content in their faeces?’ – ideas may include lack of enzymes to breakdown fats, problems with the villi preventing absorption of fatty acids etc.
  • Explain that this kind of analysis would be carried out by a biomedical scientist working in a hospital pathology lab.
  • Students can find out more about the work of biomedical scientists at

10 mins approx

Practical:

  • This practical will allow students to analyse a provided synthetic faeces sample (see Technician Notes for details) to determine its fat content.It is recommended that students work in pairs during the practical.
  • Issue students with Resource Sheet 2.1 – Analysing Faecal Fat which outlines the practical procedure.
  • The practical is designed to deliver a set of specific subject related learning outcomes and to also demonstrate the application of chemistry in a genuine real-world context. It should be explained to students that the procedure they are following is based on a genuine NHS Standard Operating Procedure which would be used by biomedical scientists working in a hospital pathology laboratory.
  • Issue each pair with Resource Sheet 2.2 – Faecal Fat Resultson which to record their results.
  • If students struggle with the calculation, Resource Sheet 2.3 – Calculation Help Sheet outlines the necessary steps.
  • Ensure that discussion of relevant safety issues is undertaken at the start.

40 mins approx

Plenary activity:

  • Students discuss their results with other groups. Tell them that the average human produces 150-200 g of faeces each day. They should be able to estimate the amount of fat that their patient passed in one day. Point out to them that a faecal fat content of more than 6 g per day is considered abnormal.
  • Point out that for the purposes of the lesson they will be asked to make a preliminary diagnosis. However, in a genuine situation although the biomedical scientist would be aware of the reasons for a doctor requesting any particular test the task of diagnosis would rest solely with the doctor responsible for the particular patient, albeit based on the results of any tests conducted by the biomedical scientists.
  • Issue students with Resource Sheet 2.4 – What is Steatorrhoea? and use this to prompt discussion about the possible causes of the patient’s high faecal fat content.

10 mins approx

Risk assessment

It is the responsibility of the supervising teacher to carry out all risk assessments with regard to this activity and to make sure that any such risk assessment complies with the requirements of the particular institution in which it is being conducted.

Extension/Homework

  • Students should consider procedural and measurement errors that occur in the procedure they have followed. Suggestions for improvements to the procedure should be made. Encourage students to research faecal fat analysis using the internet. Newer techniques include using infra-red spectroscopy to work out the fat content.

Technician Notes

Please read Resource Sheet 2.1 – Analysing Faecal Fat and Resource Sheet 2.2 – Faecal Fat Results.

Suggested procedure for making the faeces samples

Crush some All-Bran type cereal (15 g) into a coarse powder and place in a 100 cm3 beaker. Add 2 heaped spatulas of corn flour. Boil a kettle and add 10 cm3 of hot water to the mixture in the beaker and stir vigorously. Add a large spatula of golden syrup and stir vigorously. Add 10 cm3 of vegetable oil (palm oil works particularly well) and stir vigorously. The sample can now be shaped (using gloved hands) and placed on a Petri dish or plate. This will give a faeces sample with a mass of approximately 30 g (enough for one pair of students). The students have been told the sample represents 1/5 of the patient’s daily faeces production.

It should be possible to scale this preparation up to make enough synthetic faeces samples for the whole class, although thorough mixing will be required at all stages.

If it isn’t possible to prepare the samples within an hour of the lesson, they can be stored on a plate under cling-film overnight.

If the samples are prepared using the ratio of ingredients detailed above and the students carry out the practical accurately and follow the calculation steps correctly, they should arrive at the conclusion that the patient is passing in excess of 60g of fat per day in their faeces.

Notes on reagents:

3% potassium hydroxide in ethanol

Dissolve 35 g potassium hydroxide (85 % purity) in 50 cm3 water and make the volume up to 1 litre with ethanol.

33% hydrochloric acid

Carefully add 165 cm3 conc HCl to 335 cm3 distilled water.

0.1M ethanolic sodium hydroxide

Add 450 cm3 ethanol To 50 cm3 1M NaOH.

1.0% ethanolic phenolphthalein

Dissolve 1.0 g phenolphthalein in 100 cm3 ethanol.