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Summary A level year 1 carbohydrates chemical tests £3.49   Add to cart
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Summary A level year 1 carbohydrates chemical tests

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Notes from 1st year A level Biology. Achieved an A* in my final exams. Notes are based on the answers required for exam questions, based on the mark scheme requirements.

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  • November 2, 2024
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  • 2024/2025
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Carbohydrates chemical tests
summary notes
16 September 2022 09:34

Starch


- 3 drops of iodine
- Positive test goes from brown to blue/black
- For dry samples can mix with water

Iodide ions get stuck in the middle of the
amylose helix which makes it blue/black

Reducing sugar

- Equal volume of benedict's as sample
- Heat in hot water bath - 95 degrees Celsius- 5
mins
- Goes from blue to brick red

Cu2+, which is blue, gains electrons, is reduced, to
form Cu+ which is brick red

Non reducing sugar

- Test with benedict's solution to ensure it is not a
reducing sugar
- Heat the sample with acid (HCl)

This breaks the disaccharide into monosaccharides (ie
sucrose into glucose and fructose)
- Neutralise the acid with a hydrogen carbonate
(sodium hydrogen carbonate)

This is because the Benedict's solution cannot be
reduced when there are H+ ions around as the H+ will
gain electrons rather than the Cu2+ so Cu+ will not be
formed

- Benedict's test again- will go positive- brick red

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