Using a colorimeter to quantify glucose 2: Flashcards
What is the first step that we do?
= set up six test tubes
= start with a known concentration of glucose
= create a range of dilutions
What is our known solution called?
= stock solution
What is the second step that we do?
= using a syringe we place 5cm3 of of stock solution in test tube 1
= test tube 2: 4cm^3 of stock solution + 1cm^3 of distilled water (4 moles dm^-3)
= test tube 3: 3cm^3 of stock solution + 2cm^3 of distilled water (3 mole dm^-3)
= test tube 4: 2cm^3 of stock solution + 3cm^3 of distilled water (2 moles dm^-3)
= test tube 5: 1cm^3 of stock solution + 4cm^3 of distilled water (1 mole dm^-3)
= test tube 6: 5cm^3 of distilled water (NO GLUCOSE)
What is found in the seventh test tube?
= 5cm^3 of unknown solution
What is the third step that we do?
= add 5cm^3 of benedicts solution into each test tube + mix thoroughly
= place all test tubes into a boiling water 5 for 5 minutes
= benedicts reacts with the glucose and forms a red precipitate
What is the final step?
= filter red precipitate of the solution into a new test tube
= OR WE COULD USE A CENTRIFUGE
What is the first type of colorimeter we can use?
= place test tube directly into colorimeter
What are the second types of colorimeter?
= transfer all of your solutions
= into small plastic containers called cuvettes
= have 2 transparent sides and 2 transulcent sides
=
Why do we always place cuvettes into colorimeters?
= light passes through the transparent sides
What is the first step we do with the colorimeter?
= set colorimeter in red filter
= set the colirmeter to measure absorption
= place a cuvette containing just the distilled water into the colorimeter and set it to 0
=
What does setting it to 0 mean and containing just distilled water?
= consider distilled water to abosorb 0 red light,
What is the second step we do with the colorimeter?
= use the colirmeter to read the absorption of all the test tubes
What does the graph look like?
= less absorbance means more concentrated
What do we do if the absorbance of the unknown sample is too great to read off the calibration curve?
= dilute the solution and read the absorbance again
= take account the dilute factor when determining the concenration of glucose
