M2 - Redox

Question 1

Explain (using examples) when the oxidation number is zero?

Answer 1

For elements on their own (e.g. Na, K & Fe) or bonded to atoms of the same element (e.g. H₂, N₂ & Br₂)

Question 2

What is the oxidation number of Oxygen in a compound generally?

Answer 2

-2 (except in peroxides such as H₂O₂, where the oxidation no. of O is -1)

Question 3

What is the oxidation number of Hydrogen in a compound generally?

Answer 3

+1 (except in metal hydrides such as NaH or CaH₂, where the oxidation no. of H is -1)

Question 4

What is the oxidation number of Fluorine in a compound generally?

Answer 4

-1

Question 5

What is the common oxidation number of Na or K in a compound?

Answer 5

+1

Question 6

What is the common oxidation number of Mg or Ca in a compound?

Answer 6

+2

Question 7

What is the common oxidation number of Halides in a compound?

Answer 7

-1

Question 8

Provide an example for when oxygen can have an oxidation number of +2?

Answer 8

In the compound F₂O

Question 9

In ions, what must the overall oxidation number be equal to?

Answer 9

The sum of the oxidation numbers is equal to the total charge, e.g. SO₄ ^2- (S = +6 & O = -2 x 4)

Question 10

What do roman numerals mean in the use of iron(II) chloride or iron(III) chloride?

Answer 10

Iron(II) represents Fe²⁺ with oxidation number +2
Iron(III) represents Fe³⁺ with oxidation number +3

Question 11

What is the systematic name for TiCl₄?

Answer 11

Titanium(IV) chloride

Question 12

What is the systematic name for Fe₂O₃?

Answer 12

Iron(III) oxide

Question 13

What is the formula for Bromate(V)?

Answer 13

BrO₃^-

Question 14

What is the formula for Dichromate(VI)?

Answer 14

Cr₂O₇^2-

Question 15

What is oxidation in terms of electron transfer & oxidation number?

Answer 15

The loss of electrons / increase in oxidation number

Question 16

What is reduction in terms of electron transfer & oxidation number?

Answer 16

The gain of electrons / decrease in oxidation number

Question 17

Mg + CuSO₄ → Cu + MgSO₄

Explain, in terms of numbers of **electron transferred, ** the redox processes taking place in this reaction [2].

Answer 17

Magnesium (atoms) has been oxidised
AND
Because it has lost two electrons ✓

Copper (ions) has been reduced
AND
Because it has gained two electrons ✓

Question 18

3Mg + 2H₃PO₄ → Mg₃ (PO₄)₂ + 3H₂

In terms of the number of electrons transferred, explain whether magnesium is being oxidised or reduced [1].

Answer 18

Oxidised
AND
(Mg) transfers/loses/donates 2 electrons✓

Question 19

MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂

Using oxidation numbers, show what has been oxidised and what has been reduced in this reaction [2].

Answer 19

Cl (has been oxidised) from Cl = –1 to Cl = 0 ✔
Mn (has been reduced) from Mn = +4 to Mn = +2 ✔

Question 20

What is meant by the term disproportionation? [1]

Answer 20

Oxidation and reduction of the same element ✓

Question 21

2Cl₂ + 2Ca(OH)₂ → CaCl₂ + Ca(OCl)₂ + 2H₂O

This is a disproportionation reaction.

State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place [3].

Answer 21

Oxidation AND reduction of same element/chlorine
OR
Chlorine/Cl has been oxidised AND
chlorine/Cl has been reduced ✓
Oxidation
from 0 in Cl₂ to +1 in Ca(OCl)₂ OR ClO^- ✓
Reduction
from 0 in Cl₂ to –1 in CaCl₂ OR Cl^- ✓