1. Biochemical Tests Flashcards
(20 cards)
test for reducing sugars
Benedict’s reagent
original colour of Benedict’s reagent
blue liquid
what is the name reducing sugar given to
sugars that can reduce Cu2+ ions in Benedict’s reagent to Cu+ ionsin the form of copper (I) oxide
what colour does a positive Benedict’s test turn
brick red
procedure for testing for a reducing sugar
1- add Benedict’s reagent to sample
2-heat
3-if colour change observed then reducing sugar present
4-if solution remains blue, no reducing sugar
why is sucrose a non reducing sugar
-it cannot reduce cu2+
-because the chemical group needed for the reduction is involved in glycosidic bonds between the monosaccharides
how can sucrose be proven to still be a sugar
the glycosidic bond must be hydrolysed to expose the reducing group
procedure for testing for non reducing sugars
-complete Benedict’s test
-mix with HCL and boil
-cool the solution and add sodium hydroxide to make the solution alkaline
-add a few drop of Benedict’s and heat
what are the different colours a Benedict’s test can turn
yellow/green/red
why is the non reducing sugar mixed with hcl and boiled
-to break the glycosidic bond so it has hydrolysed to its monomers
why is the non reducing sugar solution cooled and sodium hydroxide solution added
-benedicts only works in alkaline solutions
-cooling prevents excessive fizzing
why must a few drops of Benedict’s reagent be added and the non reducing sugar solution heated
-to observe a colour change to identify if a non reducing sugar is present
what does the colour indicate in a non reducing sugar test
a rustier red suggests a higher sugar concentration as copper oxide has been formed
how is starch presence tested
-adding a few drops of iodine
original colour of iodine
orange/brown
positive starch in iodine result
turns blue/black
how is protein presence tested
-add biuret reagent
original colour of biuret
blue
positive biuret test result
purple
describe how to test for lipids
-sample dissolved in ethanol by shaking
-add distilled water and shake again
-white emulsion if lipids are present
