Making serial dilutions

• Making serial tenfold dilutions of a 10% glucose solution

  1. Label 4 test tubes

  2. Add 9.0cm3 of distilled water to each of the 4 labelled test tubes

  3. Add 1cm3 of the 10% glucose solution to the first test tube

  4. Put a clean bung into the neck of the test tube, hold it tightly and shake the test tube carefully ten times through 30cm to get an even mixture

  5. Using a clean pipette and a clean bung, repeat steps 2 and 3 for the three remaining test tubes, on each occasion transferring 1.0cm3 of your most recently diluted glucose solution into the next test tube that contains 9.0cm3 water
• suggest the advantage of using measured volumes from a 1cm3 glass pipette rather than 10 drops from a dropper pipette in a std Benedict's test?

  each drop has a precise volume - more accurate - more precise - smaller range between results
• list other variables that should be kept constant in a Benedict's test:

  • volume of solution in each test tube
  • time in water bath
  • temp of water bath
• suggest of control for the experiment to find the minimum sensitivity of the test for reducing sugars using Benedict's reagent:

  • volume of Benedict's
  • time in water bath
  • temp of water bath
  • should have had a 0% solution in the water bath to test if glucose could be detected