6. The rate and extent of chemical change (Paper 2)

Question 1

Some students investigated the rate of decomposition of hydrogen peroxide, H2O2
The equation for the reaction is:
2 H2O2(aq) → 2 H2O(l) + O2(g)
The catalyst for the reaction is manganese dioxide. Describe a test to identify the gas produced in the reaction.
Give the result of the test.

Answer 1

Test glowing splint
do not accept burning splint

(which) relights
ignore a pop

Question 2

What is meant by equilibrium?

Answer 2

in a closed system the rate of the forward and backward reactions are equal

Question 3

Cobalt forms coloured compounds.
A pink cobalt compound reacts with hydrochloric acid.
The reaction can be represented as:
pink cobalt compound + hydrochloric acid ⇌ blue cobalt compound + water
The forward reaction is endothermic.
When both cobalt compounds are present in a solution at equilibrium, the equilibrium mixture is purple.

(a). The equilibrium mixture is cooled.
Explain what happens to the concentration of the pink cobalt compound.

(B). More hydrochloric acid is added.
Explain what happens to the colour of the equilibrium mixture

Answer 3

(A) concentration increases (1)
(because) reaction / equilibrium moves to the left / reactant side (1)
(since the) reverse reaction is exothermic
allow (so that) temperature increases(1)

(B) becomes blue (1)
(because) reaction / equilibrium moves to the right / product side (1)
(so) concentration of blue cobalt compound increases
allow (so that) concentration of hydrochloric acid decreases (1)

Question 4

Why does cobalt form different coloured compounds?

An oxide of cobalt has the formula Co2O3
Which cobalt ion is present in this oxide?

Answer 4

Cobalt has ions with different charges
allow (cobalt is a) transition metal

Co3+