*Topic 3 - redox

Question 1

oxidation is the process of electron (1); involves an (2) in oxidation number

Answer 1

1 - loss
2 - increase

Question 2

reduction is the process of electron (1); involves a (2) in oxidation number

Answer 2

1 - gain
2 - decrease

Question 3

oxidation number rule for all uncombined elements

Answer 3

all uncombined elements have an oxidation number of 0

Question 4

oxidation number rule for elements in a compound

Answer 4

add up to 0

Question 5

oxidation number rule for monoatomic ion

Answer 5

= to the ionic charge eg. Zn2+ = +2

Question 6

oxidation number rule for polyatomic ion

Answer 6

the sum of the individual oxidation numbers of the elements add up to the charge of the ion
eg. CO3^2-; C = +4 and O = -2 sum = +4 + (3x-2) = -2

Question 7

Invariable oxidation numbers

Answer 7

Group 1 metals - +1
Group 2 metals - +2
Al = +3
H = +1 (excerpt in metal hydrides where it is -1 eg. NaH)
F = -1
Cl,Br,I = -1 except in compounds with oxygen and fluorine
O = -2 except in peroxides (H2O2) where it is -1 and in compounds with fluorine

Question 8

Name NaClO

Answer 8

Sodium chlorate (I)

Question 9

Name NaClO3

Answer 9

Sodium chlorate (V)

Question 10

Name K2SO4

Answer 10

Potassium sulfate (VI)

Question 11

Name K2SO3

Answer 11

Potassium sulfate (IV)

Question 12

Name NaNO3

Answer 12

Sodium nitrate (V)

Question 13

Name NaNO2

Answer 13

Sodium nitrate (III)

Question 14

an oxidising agent is a proton (1)

Answer 14

1 - acceptor

Question 15

A reducing agent is an electron (1)

Answer 15

1 - donor

Question 16

metals generally form ions by (1) electrons with an (2) in oxidation number to form (3) ions. Give the equation of the oxidation of zinc

Answer 16

1 - losing
2 - increase
3 - positive

Zn -> Zn^2+ + 2e-

Question 17

Non metals generally react by (1) electrons with a (2) in oxidation number to form (3) ions. Give the equation of the reaction of chlorine

Answer 17

1 - gaining
2 - decrease
3 - negative

Cl2 + 2e- -> 2Cl-

Question 18

Acid + metal -> …

Answer 18

salt + hydrogen

Question 19

Be able to write equations for reactions of metals with hydrochloric acid and sulphuric acid

Give the example of iron with sulphuric acid and its observations

Answer 19

Fe + H2SO4 -> FeSO4 + H2

Observations - effervescence because H2 gas is evolved and the metal will dissolve

Question 20

Define disproportionation

Answer 20

a reaction where an element in a single species simultaneously oxidises and reduces

Question 21

What are the 3 steps to writing half equations and give the example of the half equation of zinc

Answer 21

1. work out oxidation numbers for element being oxidised / reduced
2. Add electrons equal to the change in oxidation number; for education add e’s to reactants, for oxidation add e’s to products
3. check to see that the sum of the charges on the reactant side equals the sum of the charges on the product side

Question 22

In acidic conditions, (1) and (2)

Answer 22

1 - H+
2 - H2O

Question 23

Write the half equation for the change MnO4^- -> Mn^2+

Answer 23

MnO4^- + 8H^+ + 5e- -> Mn^2+ + 4H2O

Question 24

Write equation for the change SO4^2- -> SO2

Answer 24

SO4^2- + 4H^+ +2e- -> SO2 + 2H2O

Question 25

What is the rule when combining half equations?

Answer 25

must be equal numbers of electrons in the two half equations so that the electrons cancel out

Question 26

Combine:

Reduction: MnO4^- + 8H^+ + 5e- → Mn^2+ + 4H2O
Oxidation: C2O4^2- → 2CO2 + 2e-

Answer 26

Reduction x2
Oxidation x5

2MnO4^- + 16H^+ +5C2O4^2-→ 2Mn^2+ + 10CO2 + 8H2O