1. Do Now Hand in any PAG books that have not already been handed in
These will be given back to you on Friday
Have your revision Q booklet out so I can flick through and see how you’ve got on
Planners out – I have moved the test to next Friday (4th November) due to needing to do the chromatography PAG next Wednesday

2. Colourimetry and Biosensors
Learning objective
To know about colourimetry
Success Criteria
Explain quantitative methods to determine concentrations of a chemical in solution
To include colourimetry and biosensors

3. What is colourimetry?
Colorimetric techniques are used to identify coloured solutions and measure their concentration
It can be used to determine the concentration of certain substances in aqueous solutions
Q: Where do you think this technique would come in useful in a practical that you have done?

4. How does colourimetry work?
Colourimetry relies on coloured solutions absorbing light of a particular wavelength.
Different concentrated solutions will have a different colour intensity
Solutions that are more concentrated will have a greater colour intensity
It looks at how much light is absorbed, compared to that of a ‘blank’
The sample is place in a sample tube called a cuvette and placed in a colourimeter

5. 36% How does it work? Bulb Colorimeter Filter Cuvette with sample
Display
Cuvette with sample
Photocell

6. How does colourimetry work?
We can either measure transmission of light, or absorbance of light
A reference sample is used so that the samples to be tested can be compared to the reference
The filter is used so only a narrow band of visible light is absorbed or transmitted by the sample
If a substance is colourless, colourimetry can still be used if the substances reacts with a dye

7. How does transmission / absorbance tell us concentration?
Calibration curves are created by measuring the absorbance or transmission of a number of solutions of known concentration
A graph is then drawn
You then test an unknown sample. By taking it’s absorbance or transmission, the concentration of the sample can be found

8. Or it may be a straight line The curve may actually be a curve
% Absorbance
Concentration

9. Or it may be a straight line
% Absorbance
Concentration

10. % Absorbance Concentration
Take samples % absorbance. Draw across to curve.
% Absorbance
Draw down and read off concentration
Concentration

11. TASK:
Exam questions from Sarah. And link this to sugar and Benedict’s reagent

12. Biosensors
e.g. enzymes, antibodies
Biosensors use biological components to determine the presence, or concentration, of specific molecules e.g. glucose
STRETCH: Why would you want to be able to test for the presence of glucose? (HINT: Think medical application)
Pregnancy tests are an example of a commonly used biosensor
This tests for the presence of human chorionic gonadotrophin hormone (hCG)
This hormone is produced by the fertilised egg, and is used as marker to indicate pregnancy
It can be detected in the urine 10 days after fertilisation.
Traditionally would use dip sticks to determine if someone had diabetes. Biosensors can now be used to measure the sugar content in blood, to see if they’re controlling their blood glucose concentration

13. How a pregnancy test works
The biological component that acts as the detector is immobilised antibodies that are on a stick
These antibodies are attached to a dye
If the hormone is present in urine, it will pass up the stick, and bind to the complementary antibodies
This makes the dye become visible
There are two lines present on a pregnancy test
The first shows pregnancy
The second acts as a control, to show that the test is working
If you have two coloured lines = positive result

14. TASK: Pregnancy Test PPQ

16. Homework Revision for test that will now be next Friday (3rd November)
Review GCSE work on Enzymes, as we will be starting this topic on Friday