Topic 9.1: Oxidation and reduction

Question 1

What is transfered between atoms during REDOX reactions?

Answer 1

Electrons

Question 2

Main features of an oxidation reaction

Answer 2

a) Loss of electrons
b) Loss of hydrogen
c) Gain of oxygen

Question 3

Main features of an reduction reaction

Answer 3

a) Gain of electrons
b) Gain of hydrogen
c) Loss of oxygen

Question 4

Oxidation state (number)

Answer 4

Measure of the e- control of an atom in a compound relative to its pure element

Question 5

Representation of:

a) Oxidation state
b) Oxidation number

Answer 5

a) Roman number (Copper (I) oxide)

b) Sing + Number (+1)

Question 6

What does an increase and decrease in oxidation number mean?

Answer 6

a) An increase means oxidation

b) A decrease means reduction

Question 7

Rules for assigning oxidation states

Answer 7

a) Sum of oxidation state for a neutral compound = 0
b) Element by itself = 0
c) Monoatomic ion = Ion charge
d) Halogens = Usually /1 (+1 with oxygen)
e) Oxygen = -2 (-1 in peroxide)
f) Sum of oxidation state for a polyatomic ion = Ion charge
g) Group 1/2/3 = Always +1/+2/+3
h) Hydrogen = +1 (-1 with metals)
j) Fluorine = Always -1

Question 8

What is the main feature of the oxidation state of d-block elements and most main group non-metals?

Answer 8

Variable oxidation states

Question 9

Function of oxidizing and reducing agent

Answer 9

a) Makes oxidation happen, so the agent must take the electrons from the substance
b) Makes reduction happen, so the agent must give an electron to the substance

Question 10

IUPAC Nomenclature of a transition metal compound

Answer 10

A Roman numeral corresponding to the oxidation state is inserted in brackets after the name of the element

Question 11

Activity series

Answer 11

Arranging metals based on their relative reactivity and their strength as reducing agents

Question 12

What are the main features of metals at the top of the activity series?

Answer 12

Metals are more reactive and stronger reducing agents (more readily oxidized)

Question 13

What are the main features of metals at the bottom of the activity series?

Answer 13

Metals are less reactive and weaker reducing agents (less readily oxidized)

Question 14

What is the relationship between the difference in reactivity of two metals and time for single displacement reactions?

Answer 14

The greater the difference in reactivity of two metals, the more rapidly the reaction would occur

Question 15

When can a metal only displace another in a compound?

Answer 15

a) If it is higher in the activity series

b) More reactive elements will replace less reactive elements in a compound

Question 16

Analysis of Fe with MnO4-

Answer 16

a) In REDOX titration, Fe2+ is oxidized to Fe3+ by an oxidizing agent
b) The oxidizing agent is usually acidified KMnO4

Question 17

Iodine thiosulfate reaction

Answer 17

a) An oxidizing is used to react with excess iodide ions to form iodine
b) The liberated iodine, I2, is then titrated with sodium thiosulfate, Na2S2O3

Question 18

Biochemical oxygen demand (BOD) definition

Answer 18

The amount of O2 used by the aerobic microorganisms in H2O to decompose the organic matter in H2O over a fixed period of time

Question 19

Dissolved oxygen and levels of pollution

Answer 19

As the level of pollution in H2O increases, the dissolved O2 content decreases as the O2 is used by bacteria in decomposition reactions.

Question 20

Winkler method

Answer 20

Measure the concentration of dissolved oxygen in water

Question 21

Main ratio of O2 to S2O3 2-

Answer 21

1:4 as one mole of O2 reacts with 4 mols of S2O3 2-