Testing for starch, reducing sugars, non-reducing sugars proteins and lipids

Question 1

How do we test for starch?

Answer 1

= add iodine
= positive: blue black
= negative: remains orange

Question 2

How do we test for reducing sugars?

Answer 2

= add benedicts reageant and heat in a water bath
= positive: turns from blue to green, yellow, orange or brick red (the more red the higher concentrationof reducing sugar)- donates electrons to other species, allows benedicts to form the precipitate (copper)
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Question 3

Why does the colour change occur at the top of the solution?

Answer 3

= the hotter particles rise up so the hottes point is at the top of the test tuve- most kinetic energy

Question 4

How do we test for non-reducing sugar do we test?

Answer 4

= confirm it is not a reducing sugar, add benedicts test
= add acid to sample (HCL) and boil (heat) for 2 minutes- hydrolise the gluyco bonds to form glucose + fructose
= cool solution down by adding to a beaker of cold water and add an alkali to nuetralise
= add benedicts and heat again there will be a colour change

Question 5

What are reducing sugars?

Answer 5

= ability to donate electrons to another species
= benedicts solution has cu2+ ions and gains electrons to form a precipitate
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Question 6

How do we test for proteins?

Answer 6

= add biuret solutions- blue solition
= positive: turns from blue to purple
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Question 7

How do we test for lipids?

Answer 7

= dissolve sample in ethanol
= add distilled water
= shake it gently
= positive: white emulision
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