Electrochemistry

Question 1

What is a redox reaction?

Answer 1

A reaction in which both oxidation and reduction occur at the same time

Question 2

What is oxidation in terms of:
1. Electrons
2. Hydrogen
3. Oxidation number
4. Oxygen

Answer 2

1. The loss of electrons
2. The loss of hydrogen
3. The increase in oxidation number
4. The gain of oxygen

Question 3

What is reduction in terms of:
1. Electrons
2. Hydrogen
3. Oxidation number
4. Oxygen

Answer 3

1. The gain of electrons
2. The gain of hydrogen
3. The decrease in oxidation number
4. The loss of oxygen

Question 4

Give two examples of redox reactions.

Answer 4

Photosynthesis
Respiration

Question 5

What important thing should be remembered when forming a balanced ionic equation from two half equations?

Answer 5

We must cancel out the electrons in both equations. However, you cannot cancel out electrons that are all on one side of the arrow.

Question 6

What is a half equation?

Answer 6

An equation that either shows a reduction or oxidation reaction.

Question 7

What is the oxidation number of an uncombined element?

Answer 7

Zero

Question 8

In what compounds does hydrogen have a -1 oxidation number?

Answer 8

Metal Hydrides

Question 9

In what compounds does oxygen have a +2 oxidation number?

Answer 9

Peroxides

Question 10

When balancing redox reactions, how do we get the balancing factor for H+?

Answer 10

We ignore the H throughout the balancing process until we get to the end of it where we now calculate the total charge or the reactants and the total charge of the products ignoring H. Then we subtract the total charge of the reactants from the total charge of the products.

Question 11

What is a disproportionation reaction?

Answer 11

A reaction in which the same species is both oxidised and reduced.

Question 12

Explain what happens when the element Chlorine is reacted with an alkali.

Answer 12

Some chlorine atoms are reduced and some are oxidised in the same reaction.

Question 13

What condition does a disproportionation reaction depend on?

Answer 13

Temperature

Question 14

Write down the reduction half equation for when chlorine reacts with cold aqueous sodium hydroxide.

Answer 14

1/2Cl2 + e- —> Cl-

Question 15

Write down the oxidation half equation for when chlorine reacts with cold aqueous sodium hydroxide.

Answer 15

1/2Cl2 + 2OH- —-> ClO- +H20 + e-

Question 16

In a reduction half equation, on which side of the arrow do the electrons go?

Answer 16

Before the arrow

Question 17

In an oxidation half equation, on which side of the arrow do the electrons go?

Answer 17

After the arrow

Question 18

What are the products when chlorine reacts with hot aqueous sodium hydroxide?

Answer 18

Cl-, ClO3- and H20

Question 19

What is the oxidation state of Cl in ClO3-?

Answer 19

+5

Question 20

What is an oxidising agent?

Answer 20

A substance that oxidises another atom or ion by causing it to lose electrons while itself, it gains electrons.

Question 21

What happens to the oxidation number of an oxidising agent?

Answer 21

It decreases

Question 22

What is a reducing agent?

Answer 22

A substance that reduces another atom or ion by causing it to gain electrons while it itself loses electrons.

Question 23

What happens to the oxidation number of a reducing agent?

Answer 23

It increases