O-LevelChemistryAtomic Structure5070/22 · Oct/Nov 2020 · Q310 Marks

A drop of black ink is placed at the bottom of a beaker of water. After a time, the colour of the ink spreads throughout the water. Explain this observation in terms of the kinetic particle theory.

(a)Explain this observation in terms of the kinetic particle theory.[3]
(b)(i)In the past, ink was made from a mixture containing iron(II) ions and tannic acid. Describe a test for iron(II) ions. test observations[2]
(b)(ii)The ink darkens when used on paper. This is because iron(II) ions are oxidised to iron(III) ions. Write the ionic equation for this reaction.[1]
(b)(iii)After a time, the ink fades because of a hydrolysis reaction which is catalysed by acids. State how a catalyst increases the rate of a chemical reaction.[1]
(c)(i)Paper is made of cellulose. Cellulose is a complex carbohydrate (polysaccharide). Name one other complex carbohydrate (polysaccharide).[1]
(c)(ii)Describe how complex carbohydrates can be hydrolysed to simple sugars.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[3] 3(a) any three from: • diffusion • particles move (from place to place)/ particles collide • random (movement) of particles / particles go anywhere / particles (move) in all directions / particles disperse • intermingling of particles / mixing of particle • (bulk movement of ink particles) from higher to lower concentration
[1] 3(b)(i) (aqueous) sodium hydroxide / (aqueous) ammonia (1)
[1] 3(b)(i) (light) green precipitate (1)
[1] 3(b)(ii) Fe2+ → Fe3+ + e-
[1] 3(b)(iii) lowers the activation energy
[1] 3(c)(i) starch
[1] 3(c)(ii) reflux/heat/boil (1)
[1] 3(c)(ii) with (concentrated) hydrochloric acid (1)

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