3.1 Physical Chemistry: .7 Oxidation, reduction and redox reactions

Question 1

what is oxidation?

Answer 1

the loss of electrons

Question 2

what is reduction?

Answer 2

the gain of electrons

Question 3

what is an oxidising agent?

Answer 3

atom/molecule that accepts electrons and gets reduced its self

Question 4

what is an reducing agent?

Answer 4

atom/molecule that donates electrons and gets oxidised its self

Question 5

what does the oxidation state of an element tell you?

Answer 5

-it tells you the total number of electrons it has donated or accepted

Question 6

what are the oxidation states of elements?

Answer 6

0

Question 7

what are the oxidation states of elements bonded to identical atoms?

Answer 7

0

Question 8

what are the oxidation state of an overall compound?

Answer 8

the ion charge
e.g if has no charge the oxidation is 0
if it has a charge of -2 then the oxidation state is -2

Question 9

what is the oxidation state of a simple monatomic ion?

Answer 9

it is the same as its charge

e.g Na+ would have oxidation state of +1

Question 10

what is the oxidation state of elements in group 1 in a compound?

Answer 10

+1

Question 11

what is the oxidation state of elements in group 2 in a compound?

Answer 11

+2

Question 12

what is the oxidation state of elements in group 6 in a compound?

Answer 12

-2

Question 13

what is the oxidation state of elements in group in group 7?

Answer 13

-1

Question 14

what is the oxidation state of oxygen,

what are the exceptions?

Answer 14

• the oxidation state of oxygen is -2
• but when oxygen is in a peroxide it is -1 H2O2
• when it is bonded with fluorine it is +2 e.g OF2
• when its in O2F2 it is +1

Question 15

what is the oxidation state of chlorine? what are the exceptions?

Answer 15

• the oxidation state of Chlorine is -1

- BUT when it is bonded with Oxygen it is +1

Question 16

what is the oxidation state of Hydrogen? what are the exceptions?

Answer 16

• the oxidation state of Hydrogen is +1

- BUT when it is bonded with any element in group 1 it is -1

Question 17

what is the oxidation state of Cl in the Chlorate (I) ion (ClO-)

Answer 17

+1
because…
Cl O-
+1 -2= -1

Question 18

what does an increase in oxidation number mean?

Answer 18

• it means that the chemical has gone through oxidation

- there has been a loss of electrons

Question 19

what does a decrease in oxidation number mean?

Answer 19

• it means that the chemical has gone through reduction

- there has been a gain of electrons

Question 20

state whether this reaction is a redox reaction?

Zn + 2HCl –> ZnCl2 + H2

Answer 20

Zn + 2HCl –> ZnCl2 + H2
ox no of Zn= 0
ox no of H=+1
ox no of Cl= -1

ox no of Zn= +2
ox no of Cl= -1
ox no of H= O

Zn has gone up in oxidation number so it is oxidation
Hydrogen has gone down in oxidation number so it reduction.
Therefore this is a redox reaction.

Question 21

in this reaction state which is the oxidant and which is the reducing agent
Zn + 2HCl –> ZnCl2 + H2

Answer 21

H+ is the oxidant (it oxidised the Zn)

Zn is the reducing agent (it reduces the H+ ion)

Question 22

when balancing a combined ionic equation, what are the steps that you should follow?

Answer 22

• work out the oxidation states of each element
• work out the electrons
• work out if there water molecules and H+ ions are required
• balance the electrons