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chemical tests & quantitative methods - Coggle Diagram
chemical tests & quantitative methods
quantitative method of estimating the glucose concentration of a solution using a colorimeter
first step is to construct a calibration or reference curve using a series of known concentrations of sucrose
3) allow to cool & remove the brick-red precipitate from each tube - could centrifuge or filter
4) collect filtrate into a suitable tube & place into a colorimeter to measure the transmission
2) do a Benedict's test on all of these solutions, one by one. Use excess Benedict's but an equal amount in each case - ensures all glucose reacts - don't forget to heat the solution with the Benedict's
5) measure how much light passes through each of your tubes (transmission) & plot results on a graph
6) must remember to 'zero' the colorimeter (using distilled water) before each reading by inserting a 'blank' cuvette & pressing the zero button
1) make up several glucose concentrations (e.g.0M, 0.2M, 0.4M. 0.6. 0.8M
low concentration of glucose = very blue solution = low transmission (little light through)
high concentration of glucose = a more colourless solution = high transmission (lots of light let through)
plot readings for all the concentration to generate a calibration curve or reference curve
test the transmission of the unknown sample & use the graph to determine its glucose concentration
some colourimeter measure absorbance instead of transmission - exact inverse
high transmission = low absorbance
low transmission = high absorbance
Iodine test - starch
iodine solution = iodine (I2) dissolved in potassium iodine forming triiodide ion I3^-
add iodine solution to sample if starch present colour change from yellow-brown to blue-black
triiodide is the ion that gets trapped in an amylose helix in the starch that causes he colour change
yellow-brown --> blue-black
Emulsion test - lipids
2) filter out the solids & collect the liquid
3) pour liquid into a test tube of distilled water
1) mix food sample with ethanol - any lipids will dissolve in the ethanol
4) cloudy white emulsion = presence of lipids (made up of tiny lipid droplets that come out of solution when mixed with water
Biurets test - protein
tests for peptide bonds
Biurets solution is a mix of sodium hydroxide & copper sulphate solutions
blue copper II ions can form complexes with the nitrogen atoms in the peptide chain - once complexes formed the solution turns from clear blue to clear lilac
intensity of lilac is proportional to number of peptide bonds present
semi quantitative
Reducing sugars
heat sample with Benedict's reagent
sample forms green-->yellow-->orange-->brick-red precipitate
reducing sugar present
sample stays blue
no reducing sugar present
heat a new sample with dilute hydrochloric acid, then neutralise sample by adding sodium hydrogen carbonate. Heat sample wit Benedict's reagent
sample stays blue
no non-reducing (or reducing) sugar present
sample forms green-->yellow-->orange-->brick-red precipitate
non-reducing sugar present
