2.1.5 - Redox

Question 1

What is oxidation in terms of electrons?

Answer 1

Oxidation is the loss of electrons.

Question 2

What is the oxidation half-equation for zinc?

Answer 2

Zn → Zn²⁺ + 2e⁻

Question 3

What happens to oxidation number during oxidation?

Answer 3

It increases.

Question 4

What is reduction in terms of electrons?

Answer 4

Reduction is the gain of electrons.

Question 5

What is the reduction half-equation for chlorine?

Answer 5

Cl₂ + 2e⁻ → 2Cl⁻

Question 6

What happens to oxidation number during reduction?

Answer 6

It decreases.

Question 7

What is the oxidation number of uncombined elements?

Answer 7

Zero. For example, Zn, Cl₂, O₂, Ar all have oxidation numbers of 0.

Question 8

What must the oxidation numbers in a compound sum to?

Answer 8

Zero.

Question 9

What is the oxidation number of Na and Cl in NaCl?

Answer 9

Na = +1, Cl = –1. Total = 0.

Question 10

What must the oxidation numbers in a polyatomic ion sum to?

Answer 10

The total charge of the ion.

Question 11

What is the oxidation number of a monoatomic ion?

Answer 11

It equals its ionic charge (e.g., Zn²⁺ = +2, Cl⁻ = –1).

Question 12

What are the oxidation numbers in CO₃²⁻?

Answer 12

C = +4, O = –2 → total = -2.

Question 13

What are the common invariable oxidation numbers?

Answer 13

Group 1 = +1
Group 2 = +2
Al = +3
H = +1 (–1 in metal hydrides)
F = –1, O = –2 (–1 in peroxides, + in OF₂),
Cl/Br/I = –1 (unless with O/F).

Question 14

What is the oxidation number of hydrogen in metal hydrides?

Answer 14

-1

Question 15

What is the oxidation number of Oxygen in peroxides?

Answer 15

-1

Question 16

What is the oxidation number of oxygen in OF2?

Answer 16

+2

Question 17

Why is the oxidation number of Cl in CaCl₂ –1 and not –2?

Answer 17

Because there are two Cl atoms; the oxidation number is calculated per atom.

Question 18

What should you always calculate oxidation numbers for?

Answer 18

One atom of the element.

Question 19

What is the oxidation number of Fe in FeCl₃?

Answer 19

Cl = –1 → total Cl = –3, so Fe must be +3.

Question 20

How are oxidation numbers represented in compound names?

Answer 20

Using Roman numerals.

Question 21

What is the IUPAC name for NaClO?

Answer 21

Sodium chlorate(I)

Question 22

What is the IUPAC name for NaClO₃?

Answer 22

Sodium chlorate(V)

Question 23

What is the IUPAC name for K₂SO₄?

Answer 23

Potassium sulfate(VI)

Question 24

What is the IUPAC name for K₂SO₃?

Answer 24

Potassium sulfate(IV)

Question 25

What is the IUPAC name for NaNO₂?

Answer 25

Sodium nitrate(III)

Question 26

What is the IUPAC name for NaNO₃?

Answer 26

Sodium nitrate(V)

Question 27

What is the IUPAC name for FeCl₂?

Answer 27

Iron(II) chloride

Question 28

What is the IUPAC name for FeCl₃?

Answer 28

Iron(III) chloride

Question 29

How do metals usually react in redox?

Answer 29

They lose electrons (oxidation), forming positive ions.

Question 30

How do non-metals usually react in redox?

Answer 30

They gain electrons (reduction), forming negative ions.

Question 31

In the reaction 4Li + O₂ → 2Li₂O, what is oxidised and reduced?

Answer 31

Li is oxidised (0 → +1), O is reduced (0 → –2).

Question 32

In the reaction WO₃ + 3H₂ → W + 3H₂O, what is oxidised and reduced?

Answer 32

H is oxidised (0 → +1), W is reduced (+6 → 0).

Question 33

In the reaction 2Sr(NO₃)₂ → 2SrO + 4NO₂ + O₂, what happens?

Answer 33

O is oxidised (–2 → 0), N is reduced (+5 → +4).

Question 34

What is the general reaction between acid and metal?

Answer 34

Metal + Acid → Salt + Hydrogen

Question 35

Give an example of a metal and acid redox reaction.

Answer 35

Mg + 2HCl → MgCl₂ + H₂

Question 36

In the Mg + HCl reaction, what is oxidised and what is reduced?

Answer 36

Mg is oxidised (0 → +2), H⁺ is reduced (+1 → 0).

Question 37

Write the reaction for Fe and H₂SO₄.

Answer 37

Fe + H₂SO₄ → FeSO₄ + H₂

Question 38

What observations are made during metal-acid redox reactions?

Answer 38

Effervescence (fizzing) due to H₂ gas, metal dissolves.

Question 39

Why do only some oxygen atoms change oxidation number in some reactions?

Answer 39

Not all oxygen atoms participate in redox – depends on the compound's structure.

Question 40

In the reaction 2NH₃ + NaClO → N₂H₄ + NaCl + H₂O, what is oxidised and what is reduced?

Answer 40

N is oxidised (–3 → –2), Cl is reduced (+1 → –1).

Question 41

What are oxyanions?

Answer 41

Negative ions that have an element along with oxygen.

Question 42

What is the oxidation number of S in SO42-?

Answer 42

+6 Because combined oxygen has an oxidation number of -2. 4 x -2 = -8 The charge on the compound is -2. Sum of oxidation numbers must equal -2. So, -2 - (-8) = +6

Question 43

What is oxidation and reduction in terms of oxidation numbers?

Answer 43

Oxidation = an increase in oxidation number Reduction = a decrease in oxidation number

Question 44

What is a redox reaction? What is this also known as?

Answer 44

A reaction in which both oxidation and reduction takes place. This is also known as disproportionation.