Qualitative Tests For Biological Molecules Flashcards
What is used to test for starch?
Iodine
What is the colour change if starch is present?
Blue/black
Why does iodine turn starch blue?
When dissolved in potassium iodide the iodine forms a triiodide ion which slips into the middle of the amylose helix
What is used to test for reducing sugars?
Benedictus solution
What must happen to the reducing sugar solution?
It must be heated
What is the colour change if reducing sugars are present?
Blue
Green
Yellow
Orange/red
Define reducing sugar
A sugar which can give electrons (reduce) to other molecules
What causes the change in colour of the Benedictus solution?
The Cu2+ in benidict solution reduces into Cu+ making copper oxide giving that orange colour
What does a low concentration of reducing sugars look like?
Blue/green
What does a high concentration of reducing sugars look like?
Orange/red
What else can test for reducing sugars?
Commercially manufactured test strips
Glucose strips like for testing for diabetes etc
What test for non reducing sugars?
Benedict solution
What must first happen to the sugar solution before it can tested for nonreducing sugars?
Boiled with hydrochloride acid to hydrolyse the bonds and free up the reducing sugar group e.g. Sucrose split into glucose and fructose
What must be added to the testing solution to neutralise the acid?
Sodium hydrogen carbonate
What colours do the no reducing tests show?
The same as the reducing sugars test
