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Chemical Tests for Carbohydrates
Cake and bread each contain the same two types of carbohydrate.
Describe the chemical tests that could be used to show the presence of the two types of carbohydrate in cake.
Include a risk assessment in your answer.
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Marking points
- 1 Describes the iodine test for starch and its correct positive colour change.
- 2 Describes the heated Benedict's test for sugar/glucose and its correct positive colour change.
- 3 Gives a relevant hazard with a matching action that reduces the risk.
Full-mark answer
Make a sample of the cake for testing. Add iodine solution to one sample; a change from orange-brown to blue-black shows starch. Add Benedict's reagent to a second sample and heat it in a hot-water bath to at least 60 °C; a change from blue to green, yellow, orange or brick red shows reducing sugar. Hot water and glass can burn the skin, so use a water bath, handle hot equipment carefully and let it cool. Wear eye protection and point the test tube away from people because heated Benedict's reagent may spit.
Why this answer loses marks
Add iodine and Benedict's solution; wear goggles.
This omits both positive colour changes, the heating needed for Benedict's, and a hazard matched to its control.