Redox Reactions

Question 1

Define redox reaction

Answer 1

Redox reaction is a reaction where oxidation and reduction occur at the same time

Question 2

Define oxidation/reduction in terms of oxygen

Answer 2

Gain/Loss of oxygen by substance (with no other changes to the substance)

Question 3

Define oxidising agent

Answer 3

A substance that oxidises another substance while itself is being reduced

Question 4

Explain oxidising agent in CO(g) + H2O(g) reaction in terms of oxygen

Answer 4

H2O is the oxidising agent as H2O loses oxygen to CO and oxidises CO to CO2

Question 5

Define oxidation/reduction of substance in terms of hydrogen

Answer 5

Loss/Gain of hydrogen by substance(with no other changes to the substance)

Question 6

Explain reducing agent in reaction Cl2(g) +H2S(g) in terms of hydrogen

Answer 6

H2S is the reducing agent because H2S loses hydrogen to Cl2 and reduces Cl2 to HCl

Question 7

Define oxidation/reduction in terms of electrons

Answer 7

Loss/Gain of electrons by substance

Question 8

Define oxidising agent in reaction Na(s) + Cl2(g) in terms of electrons

Answer 8

Cl2 is the oxidising agent as Cl2 gains electrons from Na and oxidises Na to Na+

Question 9

Define oxidation state/oxidation number

Answer 9

The charge an atom would have if it existed as an ion

Question 10

Define electronegativity

Answer 10

The ability of an atom to attract the shared pair of electrons towards itself in a covalent bond

Question 11

How does electronegativity vary in a group and period

Answer 11

Increase across a period decrease down a group

Question 12

Arrange following in terms of electronegativity: Br, N, F, O, H, C, Cl, I

Answer 12

F, O, Cl, N, Br, I, C, H

Question 13

Define oxidation/reduction in terms of oxidation state

Answer 13

The increase/decrease in oxidation state of an element in a substance during a reaction

Question 14

Explain substance which is reduced in Mg + CuO in terms of oxidation state

Answer 14

CuO is reduced because the oxidation state of copper decreases from +2 in CuO to 0 in Cu

Question 15

Why is HCl + NaOH not a redox reaction

Answer 15

The oxidation states of all elements in the substances remain unchanged during the reaction

Question 16

Observation for acidified aqueous potassium manganate(VII)

Answer 16

Purple acidified aqueous potassium manganate(VII) turns colourless (testing reducing agent)

Question 17

Observation for aqueous potassium dichromate(VI)

Answer 17

Orange acidified aqueous potassium dichromate(VI) turns green (testing reducing agent)

Question 18

Observation for aqueous iron(III) chloride

Answer 18

Yellow aqueous iron(III) chloride solution turns pale green (testing reducing agent)

Question 19

Observation for aqueous iodine

Answer 19

Brown aqueous iodine turns colourless (testing for reducing agent)

Question 20

Observation for aqueous potassium iodine

Answer 20

Colourless aqueous potassium iodide turns brown (black solid may be formed if excess iodine is formed) (testing for oxidising agent)

Question 21

Observation for aqueous iron(II) sulfate

Answer 21

Pale green aqueous iron(II) sulfate turns yellow (testing for oxidising agent)

Question 22

Define disproportionation reaction

Answer 22

A reaction where a single substance is both oxidised and reduced in the reaction