3.4- Testing For Carbohydrates Flashcards
What is meant by reducing sugars?
All monosaccharides and some disaccharides are reducing sugars. This means that they can donate electrons to (or reduce) another molecule/chemical.
Benedict’s test for reducing sugars.
- Place sample in a boiling tube in liquid form.
- Add an equal volume of Benedict’s reagent.
- Heat the mixture gently in a water bath for 5mins.
- reducing sugars react with copper ions in Benedict’s reagent. Results in the addition of electrons to the blue Cu2+ ions, reducing them to brick red Cu+ ions.
- brick red precipitate represents positive result.
- the more reducing sugar present, the more precipitate formed so colour depends on conc of reducing sugars present = qualitative test.
Test for starch.
Iodine test:
- A few drops of iodine dissolved in potassium iodide solution are mixed with the sample.
- Yellow/brown to purple/black indicates presence of starch.
What is the use if reagent strips?
Can be used to test for reducing sugars, most commonly glucose.
advantage: with the use of a colour coded chart, concentration of the sugar can be determined.
What are the 2 quantitative methods to find concentration?
- Colorimetry
2. Biosensors
Explain colorimetry.
Allows you to estimate glucose present in a solution.
It quantitatively measures the absorbance/transmission of light by a coloured solution.
More concentrated solution= higher absorbance & less transmission.
- Place filter in colorimeter.
- Calibrate using distilled water.
- Benedict’s test done on a range if conc.
- Solutions filtered to remove precipitate.
- % transmission of solution measured.
- Calibration curve plotted then used to calculate concentration in unknown sample.
Explain biosensors.
They use biological components to find the presence and concentrations of molecules.
Analyte= compound under investigation.j
- Molecular recognition= a protein/ single DNA strand is immobilised to a surface which will interact/ bind to the specific molecule under investigation.
- Transduction = transducer detects changes (eg. pH) and produces a response (such as a dye or electric current being released).
- Display= produces visible (quantitative or qualitative) signal.