KIDNEY STONE ANALYSIS

Transcription

1 KIDNEY STONE 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 carry out a titrimetric analysis. Calculate the percentage by mass of calcium in a synthetic kidney stone. Analyse the data and use reference information to formulate a diagnosis for the patient. Evaluate the method and suggest improvements. Appreciate how experimental procedures are used in a real-world context. Lesson Outcomes By the end of the lesson: All students will be able to describe and carry out an experimental procedure to analyse the calcium content of a kidney stone. Most students will be able to suggest a reliable diagnosis of the patient based on provided data and reference information. Some students will be able to suggest a more reliable experimental procedure with appropriate justification. Time required Approximately one hour. Specification Links Board Unit Spec (reactions and equations) (Group 2 metals) AQA 3 Practical Skills (multi-dentate ligands) 6 Practical Skills (reactions and equations) (groups 2 and 7) Edexcel 3 Laboratory Skills (transition metals polydentate ligands) 6 Laboratory Skills F (moles and equations) (Group 2) OCR A F323 Practical Skills F (transition metals polydentate ligands) F326 Practical Skills OCR B (Salters) F331 F333 F334 (formulae, equations and amount of substance and group 2 chemistry) Chemistry in Practice (inorganic chemistry and the periodic table polydentate ligands) 1

2 Key Stage 5 CHeMIStRy LeSSon plan 1 - KIdney Stone analysis Materials and equipment required For each student Resource Sheet 1.1 What are Kidney Stones? For each pair of students 1 pre-prepared synthetic kidney stone (see Technician Notes) Pestle and mortar Plastic weighing boat Spatula Distilled water wash bottle 500 cm 3 volumetric flask Plastic Pasteur pipettes (several) cm 3 conical flasks 10 cm 3 transfer (volumetric) pipette and filler 50 cm 3 burette Resource Sheet 1.2 Analysing a Kidney Stone Resource Sheet 1.3 Kidney Stone Analysis Results Resource Sheet 1.4 Calculation Help Sheet Resource Sheet 1.5 Making Your Diagnosis For the whole class mol dm -3 solution of EDTA di-sodium salt in water (allow 100 cm 3 per group). 100 cm 3 25% (w/v) sodium hydroxide solution in water (each group needs a few drops per titration). Solution of calcon carboxylic acid (~ 0.20g) in 50 cm 3 water (each group needs a few drops per titration). Plenty of distilled water (at least 500 cm 3 per group). 2

3 Lesson structure (including approximate timings) Intro. Activity: Ask the students to answer the question What is a kidney stone? 10 mins approx This could have been set as a research task for homework at the end of a previous lesson. Elicit the students ideas. Issue students with Resource Sheet 1.1 What are Kidney Stones? to provide them with some background information. This can then be used to promote further discussion. Explain that analysis of the content of kidney stones is a useful diagnostic tool and this kind of analysis would be carried out by a biomedical scientist (BMS) working in a hospital pathology lab. Students can find out more about the role of biomedical scientists in the NHS at Practical: 40 mins approx This practical will allow students to analyse a provided synthetic kidney stone (see Technician Notes for details) in order to deduce its calcium content. It is recommended that students work in pairs during the practical. 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 students with Resource Sheet 1.2 Analysing a Kidney Stone which outlines the practical procedure. Issue each pair with Resource Sheet 1.3 Kidney Stone Analysis Results. Students can record their results on this sheet and perform the calculation required. Resource Sheet 1.3 comes in four versions, relating to patients A, B, C and D. Each patient has a unique set of oxalate, phosphate, cystine and uric acid levels, which together with the measured calcium level will allow students to make different diagnoses for each patient. If students struggle with the calculation, Resource Sheet 1.4 Calculation Help Sheet outlines the necessary steps. Ensure that discussion of relevant safety issues is undertaken at the start. Plenary activity: After completing the analysis and recording their results, issue students with 10 mins approx Resource Sheet 1.5 Making Your Diagnosis, which will help them to diagnose the patient s problem based on the results of their analysis. 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. Any diagnosis made by the doctor would also be based on other information such as scans of the stones etc. Students can then be invited to discuss the diagnosis of their patient with the rest of the class. 3

4 Key Stage 5 CHeMIStRy LeSSon plan 1 - KIdney Stone analysis 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. 4

5 Technician notes Please read Resource Sheet 1.2 Analysing a Kidney Stone and Resource Sheet 1.3 Kidney Stone Analysis Results. Making the kidney stones In order to make stones that hold together well, it is advised that calcium hydroxide and oxalic acid dihydrate are used. Small amounts of sand and/or uric acid may also be added. Yellow food dye may be added, but do check that your particular food dye doesn t interfere with the calcon indicator first. Suggested procedure: Combine calcium hydroxide (1.48g; mol) and oxalic acid dihydrate (1.26g; mol) in a mortar and grind to a fine powder with a pestle. Add distilled water dropwise with stirring, until the mixture has the consistency of tooth paste. Other ingredients may be added at this point if desired. This amount of mixture is suitable for making about 10 stones. These can be shaped and placed on a Petri dish (or similar). The stones should then be baked overnight in an oven at 100 C or above. Note that the molar ratio of calcium hydroxide to oxalic acid is 2:1. Allowing for evaporation of water, this should give a stone with an approximate calcium content (by mass) of %. The students can compare their obtained values with this. Other notes: Calconcarboxylic acid indicator solution (200mg/50 cm 3 water) should be made freshly. Calconcarboxylic acid can be purchased from the usual chemical suppliers. EDTA disodium salt is also readily available from the usual suppliers. It is essential that students carry out the titration under alkaline conditions by adding a few drops of 25% NaOH solution. About 15.0 cm 3 of M EDTA solution will be required to complex all the free calcium ions in this experiment, but a number of factors could contribute to students getting variable results. If the volumes required are found to be very high, one could further dilute the solution made from the kidney stone. 5