redox reactions

Question 1

describe reduction in terms of electrons

Answer 1

gain of electrons

Question 2

describe reduction in terms of oxidation number

Answer 2

decrease in oxidation number

Question 3

describe oxidation in terms of electrons

Answer 3

loss of electrons

Question 4

describe oxidation in terms of oxidation number

Answer 4

increase in oxidation number

Question 5

state the oxidation number for an element

Answer 5

0

Question 6

state the oxidation number for combined H

Answer 6

+1

Question 7

state the oxidation number for combined O

Answer 7

-2

Question 8

state the oxidation number for an ion

Answer 8

equal to the ion’s charge

Question 9

describe an oxidising agent

Answer 9

• takes electrons from another species (oxidises it)
• is reduced

Question 10

describe a reducing agent

Answer 10

• adds electrons to another species (reduces it)
• is oxidised

Question 11

state the oxidising and reducing agent in the following equation:

2Ag+ + Cu –> Cu2+ + 2Ag

Answer 11

Ag = oxidising agent
Cu = reducing agent

Question 12

how are redox equations balanced?

Answer 12

by balancing the electrons across both equations

Question 13

balance the following redox equations

H2O2 + 2e- –> 2OH-
Cr3+ + 8OH- –> CrO4 2- + 4H2O + 3e-

Answer 13

3H2O2 + 6e- –> 6OH-

2Cr3+ + 16OH –> 2CrO4 2- + 8H2O + 6e-

Question 14

describe the process for balancing half equations

Answer 14

1. write species before and after reaction
2. balance atoms except O and H
3. balance O with H2O and H with H+
4. balance charges with e-

Question 15

balance the following equation

Fe2+ –> Fe3+

Answer 15

Fe2+ –> Fe3+ + e-

Question 16

balance the following equation

MnO4- –> Mn2+

Answer 16

1. MnO4- –> Mn2+
2. MnO4- –> Mn2+ + 4H2O
   MnO4- + 8H+ –> Mn2+ + 4H2O
3. MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

Question 17

in a redox half equation, where are the electrons positioned for reduction

Answer 17

on the left

Question 18

in a redox half equation, where are the electrons positioned for oxidation

Answer 18

on the right

Question 19

describe the process for combining half equations into a full ionic equation

Answer 19

• balance electrons
• cancel electrons
• combine

Question 20

state the oxidation number for oxygen in fluorides

Answer 20

+2

Question 21

state the oxidation number for oxygen in peroxides

Answer 21

-1

Question 22

state the oxidation number for hydrogen in metal hydrides

Answer 22

-1

Question 23

define oxidation number

Answer 23

the charge that a molecule would have, if the electrons in each bond belonged to the more electronegative element