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chemistry igcse acapprinted 135 · PDF 135
145 pagesrevision 46934
printed 135 · PDF 135
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D
✗
✗
The correct answer is B, because the forward reaction is that of dehydration, so to reverse it we would need to
add more water but not heat it. A and C are incorrect because adding heat would cause it to remain as a forward
reaction, while D is incorrect because we need to add water to shift the equilibrium.
5. Substance Y is a pink solid.When substance Y is heated gently it becomes a blue solid.When the blue solid is
cooled down it remains blue.When water is added to the blue solid it becomes pink.
What is substance Y?
A anhydrous cobalt(II) chloride
B anhydrous copper(II) sulfate
C hydrated cobalt(II) chloride
D hydrated copper(II) sulfate
The answer is C, because hydrated cobalt (II) chloride is pink in colour and turns to blue anhydrous cobalt (II)
chloride when heated. It cannot be A or B, because the substance reacts to heat to produce its anhydrous form,
meaning that it must be hydrated, and it cannot be D because it is pink, not blue.
6. Aqueous bromine is an equilibrium mixture.
Br2(aq) + H2O(l) ⇌ OBr –(aq) + Br –(aq) + 2H+(aq)
Aqueous bromine is orange in colour. The species on the right-hand side of the equation are
colourless.Changes are made to three separate portions of the equilibrium mixture.Which row shows how the
colour of the mixture changes when a small amount of each substance is added?
Adding sulfuric acid
Adding solid sodium
bromide
Adding water
A
Darker orange
Darker orange
Darker orange
B
Darker orange
Darker orange
Paler orange
C
Darker orange
Paler orange
Darker orange
D
Paler orange
Darker orange
Paler orange
The answer is B, because an increase in the products, i.e sulfuric acid and sodium bromide, will cause the
equilibrium to shift to the left and thus turn darker, while adding a reactant, i.e water, will cause the equilibrium
to shift to the right and thus the solution will turn lighter.A and C are incorrect because adding water would not