Add. Prac. 2- Colourimetry

• What are the basic steps of this practical?

  .

  1. Serial dilution
  2. Benedict's test
  3. Cuvettes
  4. Colorimeter
• How do you prepare a serial dilution for the glucose solution?

  6 test tubes:

  1. Add 20ml of 2M of solution into the first test tube
  2. Remove 10ml from 2M test tube + 10ml of distilled water= 1M
  3. Remove 10ml of previous test tube + 10ml of distilled water
  4. Repeat step 3 until all 6 test tubes are used. (Remove 10ml of the 0.0625M solution to secure even amount across all.
• What is the name of the starting test tube in serial dilution?

  Stock solution
• How is the Benedict's test carried out?

  .

  1. Add the same amount of Benedict's reagent into each test tube (eg. 2cm3)
  2. Place in water bath for 10 minutes at 80 degrees
  3. Take test tubes out of the bath and leave to cool for 5 minutes
• Why are the test tubes left to cool after being in the water bath?

  They must be left for the solutions to separate and the precipitate to sink to the bottom.
• How are the solutions prepared before using the colorimeter?

  Placed in cuvettes:

  1. Use a pipette to remove the top layer of the solutions and place into a cuvette
  2. Place a cuvette cap on the top
  3. Repeat for all the 6 solutions
• How do we create a control cuvette?

  Place water and Benedict's reagent into a cuvette and place a cap on top.

  This is used to calibrate the colorimeter.
• What is a precaution you must take when handling the cuvettes?


  Only touch the corners as fingerprints may effect the readings on the colorimeter.
• How to operate the colorimeter?

  .

  1. Ensure it is set to the red filter
  2. Select either absorbency or transmission
  3. Calibrate by placing the control cuvette in and press calibrate button
  4. Add each cuvette into the colorimeter and collect the results.
  5. Between each reading, re-calibrate it.
• What is the dilution series calculation?

  C1 x V1 = C2 x V2

  C1 = concentration of stock solution

  V1 = volume of stock solution used to create new concentration

  V2 = volume of new solution you are making
• What does V2 equal?

  V2 = V1 + volume of distilled water to dilute with

  (You must use both this and the dilution series calculation in an exam question)