REDOX

Question 2

What is the KOHES mnemonic used for?

Answer 2

To remember the order in balancing half equations: K (K atoms)

Question 3

What is oxidation in terms of oxygen?

Answer 3

Gain of oxygen.

Question 4

What is reduction in terms of oxygen?

Answer 4

Loss of oxygen.

Question 5

What is oxidation in terms of electrons?

Answer 5

Loss of electrons (OIL - Oxidation Is Loss).

Question 6

What is reduction in terms of electrons?

Answer 6

Gain of electrons (RIG - Reduction Is Gain).

Question 7

What is a redox reaction?

Answer 7

A reaction where both oxidation and reduction occur.

Question 8

What is a reducing agent?

Answer 8

A substance that donates electrons and is oxidised.

Question 9

What is an oxidising agent?

Answer 9

A substance that accepts electrons and is reduced.

Question 10

What is the oxidation state of an uncombined element?

Answer 10

0

Question 11

What is the oxidation state of a simple ion?

Answer 11

Equal to its charge.

Question 12

What is the oxidation state of oxygen in most compounds?

Answer 12

–2 (except in peroxides -1

Question 13

What is the oxidation state of hydrogen in most compounds?

Answer 13

+1 (except in metal hydrides -1).

Question 14

What is the oxidation state of fluorine in compounds?

Answer 14

–1 (always).

Question 15

What is the oxidation state of chlorine in compounds?

Answer 15

Usually –1

Question 16

What is the sum of oxidation states in a neutral compound?

Answer 16

0

Question 17

What is the sum of oxidation states in a polyatomic ion?

Answer 17

Equal to the ion’s overall charge.

Question 18

How can oxidation states be used to identify redox reactions?

Answer 18

If oxidation state increases → oxidation; if it decreases → reduction.

Question 19

What is disproportionation?

Answer 19

A redox reaction where the same species is both oxidised and reduced.

Question 20

Give an example of disproportionation involving chlorine and water.

Answer 20

Cl₂ + H₂O → HCl + HClO

Question 21

What is a half equation?

Answer 21

An equation showing either the oxidation or reduction half of a redox reaction

Question 22

What are the steps to balance a half equation in acidic solution?

Answer 22

Balance atoms other than O and H

Question 23

Write the half equation for reduction of permanganate ion in acid.

Answer 23

MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O

Question 24

Write the half equation for oxidation of iron(II) ion.

Answer 24

Fe²⁺ → Fe³⁺ + e⁻

Question 25

Combine the half equations: Fe²⁺ → Fe³⁺ + e⁻ and MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O.

Answer 25

5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O

Question 26

What colour change occurs in titration using acidified potassium manganate(VII)?

Answer 26

Purple (MnO₄⁻) turns colourless (Mn²⁺).

Question 27

Why is no indicator needed in manganate titrations?

Answer 27

MnO₄⁻ is self-indicating by colour change.

Question 28

Write the ionic equation for disproportionation of chlorine in cold

Answer 28

dilute sodium hydroxide.

Question 29

Write the ionic equation for reduction of dichromate ion in acid.

Answer 29

Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O

Question 30

Write the ionic equation for oxidation of iodide ions to iodine.

Answer 30

2I⁻ → I₂ + 2e⁻

Question 31

Write the ionic equation for reaction of iodine with thiosulfate ions.

Answer 31

I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻

Question 32

What is the role of a reducing agent in redox?

Answer 32

Donates electrons and is oxidised.

Question 33

What is the role of an oxidising agent in redox?

Answer 33

Accepts electrons and is reduced.

Question 34

What is the oxidation and reduction mnemonic?

Answer 34

OIL RIG (Oxidation Is Loss

Question 35

How do you calculate oxidation state of an element in a compound?

Answer 35

Assign known oxidation states and solve so sum equals overall charge.