DP Chemistry (last assessment 2024)

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Question 18M.3.hl.TZ1.10b

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Date May 2018 Marks available [Maximum mark: 3] Reference code 18M.3.hl.TZ1.10b
Level hl Paper 3 Time zone TZ1
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 3]
18M.3.hl.TZ1.10b

Anthocyanins are naturally occurring plant pigments. Depending on the solution pH, they can exist as quinoidal bases or flavylium cations as shown in section 35 of the data booklet.

(b)

Explain why the blue colour of a quinoidal base changes to the red colour of a flavylium cation as pH decreases.

[3]

Markscheme

gaining protons

decreases electron density/extent of conjugation «in aromatic backbone»

increases energy of electron transitions

 

[3 marks]

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