C3: REDOX Reactions

Question 1

what is a redox reaction?

Answer 1

type of chemical reaction which involves transfer of electrons between two chemical species

Question 2

OIL RIG mnemonic means

Answer 2

Oxidation Is Los ; Reduction Is Gain

Question 3

State the oxidation rules for the following

1. atom in free uncombined state _______
2. sum of the oxidation numbers of all the atoms or ions in a compound_____
3. oxidation number of a monoatomic ion in an ionic compound___________
4. oxidation number of hydrogen in a compound or polyatomic ion is (a)_____________ except in hydrides where it is (b)______________
5. oxidation number of oxygen in a compound or polyatomic ion is (a)_____________ , except in peroxides where it is (b)______________
6. the sum of the oxidation numbers of the atoms in a plyatomic ion is____________
7. the elements in covalent compounds or polyatomic ions (a)______________ except (b)______________ and (c) __________

Answer 3

1. 0
2. 0
3. same as the charge on the ion
4. (a) +1 , (b) -1
5. (a) -2, (b) -1
6. the same as the charge on the ion
7. (a)may vary, (b) hydrogen, (c) oxygen

Question 4

an oxidising agent causes the oxidation number of an element in free or combined state to (1)__________ by causing it to (2)__________ electrons. the oxidising agent itself is (3)___________ because it (4) ___________ electrons in the process.

Answer 4

1. increase
2. lose
3. reduced
4. gains

Question 5

a reducing agent causes the oxidation number of an element in free or combined state to (1)__________ by causing it to (2)__________ electrons. the reducing agent itself is (3)___________ because it (4) ___________ electrons in the process.

Answer 5

1. decrease
2. gain
3. oxidised
4. loses

Question 6

A (1)___________ causes the oxidation number of an element in free or combined state to decrease by causing it to (2)__________ electrons. The (3)________ agent itself is (4)___________ because it loses electrons in the process.

Answer 6

1. reducing agent
2. gain
3. reducing
4. oxidised

Question 7

A (1)___________ causes the oxidation number of an element in free or combined state to increase by causing it to (2)__________ electrons. The (3)________ agent itself is (4)___________ because it loses electrons in the process.

Answer 7

1. oxidising agent
2. lose
3. oxidising
4. reduced

Question 8

examples of oxidising agents

Answer 8

• acidified potassium manganate(VII) solution
• acidified potassium dichromate(VI) solution
• aqueous iron(III) salts
• Sodium chlorate solution
• hot concentrated suphuric acid
• dilute or concentrated nitric acid
• oxygen
• chlorine
• magnesium oxide

Question 9

examples of reducing agents

Answer 9

• potassium iodide solution
• aqueous iron(II) salts
• hydrogen sulfide gas
• concentrated hydrochloric acid
• hydrogen
• carbon
• carbon monoxide
• reactive metals

Question 10

identify the oxidising and reducing agents

1. acidified potassium dicromate(VI)
2. CO
3. H₂
4. O₂

Answer 10

1. oxidising
2. reducing
3. reducing
4. oxidising

Question 11

identify the oxidising and reducing agents

1. H₂S
2. acidified KMNO₄(aq)
3. NaClO(aq)
4. conc. HCL

Answer 11

1. reducing
2. oxidising
3. oxidising
4. reducing

Question 12

identify the oxidising and reducing agents

1. Fe³⁺(aq)
2. Fe²⁺(aq)
3. C
4. Na

Answer 12

1. oxidising
2. reducing
3. reducing
4. reducing

Question 13

identify the oxidising and reducing agents

1. Ca
2. Mg
3. Ag
4. HNO₃(aq)
5. H₂SO₄(l)

Answer 13

1. reducing
2. reducing
4. oxdising
5. reducing

Question 14

identify the oxidising and reducing agents

1. KI(aq)
2. NaClO(aq)
3. H₂
4. CO
5. H+/K₂Cr₂O₇(aq)
6. Al

Answer 14

1. reducing
2. oxidising
3. reducing
4. reducing
5. oxidising
6. reducing

Question 15

two substances that act as both oxidising and reducing agents

Answer 15

• SO₂
• H+/H₂O₂(aq)

Question 16

How to test for the presence of an oxidizing agent

Answer 16

Add it to a known reducing agent which will give a visible Color change when oxidized

Question 17

How to determine if a substance is a reducing agent

Answer 17

Add it to unknown oxidizing agent which will give a visible color change when reduced

Question 18

To determine if a substance is a reducing agent add it to a known (1) ______________ , most commonly (2)_________________ or 3) __________________

Answer 18

1. Oxidizing agent 2. Acidified potassium manganate(VII) 3. Acidified potassium dichromate(VI)

Question 19

To determine if a substance is an oxidizing agent add it to a known (1) ______________ , most commonly (2)_________________ or 3) __________________

Answer 19

1. Reducing agent 2. Potassium iodide solution 3. Aqueous solution of iron(III) salt

Question 20

how do redox reactions account for rusting?

Answer 20

moisture and oxygen react with iron and its alloy steel causing the iron to be oxidized to form hydrated iron(III) oxide (Fe₂O₃.xH₂O)

Question 21

chlorine bleaches contain (1)_____________ and oxygen bleaches contain (2)_____________ which are both (3)_____________ and will remove coloured stains by oxidising the coloured dyes to thier colourless forms.

Answer 21

1. sodium chlorate(I) (NaClO)
2. H₂O₂
3. Oxidising agents

Question 22

explain the browning of fruits and vegetables when they are cut

Answer 22

enzymes in the cells on the cut surfaces of the fruit or vegetable use the oxygen in the air to oxidise certain chemicals in the cells to brown compounds called melanins

Question 24

enzymes in the cells on the cut surfaces of some fruits or vegetables use the (1)_____________ in the air to (2)____________ certain chemicals in the cells to brown compounds called (3)____________. This is an example of a (4) _____________

Answer 24

1. oxygen
2. oxidise
3. melanins
4. redox reaction

Question 25

how is redox applied in preserving food

Answer 25

Sodium sulphite and sulphur dioxide are used as food preservatives due to their properties as reducing agents. they prevent spoilage by preventing oxidation and reduce melanins back to their colouress form

Question 26

These 2 food preservatives, (1) ____________ and (2)\_\_\_\_\_\_\_\_\_\_ prevent wine spoilage by preventing its (3)\_\_\_\_\_\_\_\_\_\_\_\_\_\_ to (4)\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 26

1. sodium sulphite 2. sulfur dioxide 3. oxidation 4. vinegar

Question 27

These 2 food preservatives, (1) ____________ and (2)\_\_\_\_\_\_\_\_\_\_ prevent oxidation of (3)\_\_\_\_\_\_\_\_\_\_\_\_ in fruits and (4) \_\_\_\_\_\_\_\_\_\_\_, thus preveting their spoilage

Answer 27

1. sodium sulphite 2. sulphur dioxide 3. vitamin C 4. fruit juices

Question 28

identify the oxidising/reducing agent/s found in each 1. CuSO₄ + Fe → Cu + FeSO₄ 2. CuO + H₂ → Cu + H₂O

Answer 28

1. CuSO₄ - oxidizing agent; Fe - reducing agent 2. CuO - oxidizing agent; H₂ - reducing agent

Question 29

what substance is oxidised and what is the oxidising agent in the reactions below? 1. Ca(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂(g) 2. Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Answer 29

1. Ca is oxidized by H₂SO₄(aq) 2. Zn(s) is oxidised by H₂SO₄(aq)

Question 30

What substance is reduced in this reaction? 1. C₂H₄(g) + 3 O₂(g) → 2 CO₂(g) + 2 H₂O(g) 2. Ca(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂(g)

Answer 30

1. Oxygen 2. H₂SO₄(aq)