Section 4 redox

Question 1

Oxidation definition

Answer 1

An oxidation is a loss of electrons from reactants in a reaction.

Question 2

Reduction definition

Answer 2

A reduction is a gain of electrons by reactants in a reaction.

Question 3

Page of the data booklet you need for ion electron equations

Answer 3

The electrochemical series

Question 4

How do you identify if a reaction is an oxidation

Answer 4

The electrons are at the end of the equation. (Therefore being lost from reactants)

Question 5

How do you tell if a reaction is a reduction reaction

Answer 5

The electrons are at the start of the reaction (therefore being gained by the reactants.)

Question 6

When writing down an oxidation ion electron equation always remember

Answer 6

To flip the ion electron equation
And if with a reduction reaction make sure it is higher on the electrochemical series.

Question 7

When writing down a reduction ion equation always remember

Answer 7

To keep the equation the same way round,
To make sure that the equation is lower than the oxidation.

Question 8

Redox reaction definition

Answer 8

A reaction where both a reduction and an oxidation occur.

Question 9

How do you produce a redox equation

Answer 9

You have to balance the number of electrons on each reaction
Then you must cancel out the electrons and any other shared chemicals.
Then you combine the reaction.

Question 10

Oxidising agent definition

Answer 10

A substance that oxidises another substance, and itself is reduced, meaning it is an electron acceptor /oxygen donor /hydrogen acceptor.

Question 11

Reducing agent definition

Answer 11

A substance that reduces another substance, it itself will undergo oxidation, meaning it is an electron donor/ oxygen acceptor/ hydrogen donor.

Question 12

Where are oxidising agents found on the electrochemical series

Answer 12

The bottom left hand column

Question 13

Where are the strongest reducing agents found in the electrochemical series

Answer 13

At the top of the right hand column

Question 14

Where are strong oxidising agents found on the periodic table

Answer 14

In the halogens / group 7

Question 15

Where are strong reducing agents found on the periodic table

Answer 15

On the alkali metals / group one of the periodic table .

Question 16

Reducing agents I need to know

Answer 16

Carbon monoxide

Question 17

Oxidising agents I need to know

Answer 17

Hydrogen peroxide (H2O2)
Dichromate (Cr207 2-)
permanganate Mn04-

Question 18

What must be added to oxidising agents

Answer 18

Acid - to supply hydrogen ions

Question 19

Why must acid be added to oxidising agents

Answer 19

To supply hydrogen ions.

Question 20

Features of oxidising agents

Answer 20

Occur when there is a:
Gain of electron
Loss of oxygen
Gain of hydrogen

Question 21

Reducing agents features

Answer 21

Reducing agents:
Lose electrons
Gain oxygen
Lose hydrogen

Question 22

Metal atoms to ions

Answer 22

Go from neutral to positively charged, meaning they lose electrons, meaning they are oxidised and reducing agents.

Question 23

Metal ions to metal atoms

Answer 23

Go from positively charged to neutral so they gain electrons, meaning they are reduced and the oxidising agent.

Question 24

Non metal atoms to non metal ions

Answer 24

Go from neutral to negative, so gain electron, undergoing reduction and becoming an oxidising agent.

Question 25

Non metal ions to non metal atoms

Answer 25

Go from negatively charged to neutral, therefore are losing electrons, meaning they are oxidised and the reducing agent.

Question 26

Writing ion electron equations from scratch stages

Answer 26

Balance number of non oxygen atoms Add water to one side balancing oxygen Add hydrogen + to the other to balance out hydrogen Add electrons to cancel out the difference in charge.

Question 27

Uses of oxidising agents

Answer 27

Sodium hypochlorite is used to kill fungi, bacteria and viruses. Potassium permanganate is used in killing bacterial infections in fish. Hydrogen peroxide is used in bleaching clothes and hair. (By breaking down colour compounds.

Question 28

Why may an indicator not be necessary when doing a redox titration

Answer 28

It may be self indicating

Question 29

Titration technique and skills

Answer 29

Must use a standard flask when measuring out a standard solution, The burette must be at eyesight The burette must be rinsed through before the titration begins The burette must have a filter funnel in the top to pour liquid in and removed when the titration is happening A white object like paper should be put under the conical flask to easily determine the end point A rough titre must be used The results should be concordant. Conical flask must be swirled throughout titrations.

Question 30

Concordant results

Answer 30

Results within 0.2 cm3 of each other.

Question 31

Calculating a redox titration. When finding mass

Answer 31

Use N=CV Then mole ratio M =n times GFM Then multiply to sample.

Question 32

Calculating redox titration when finding concentration.

Answer 32

N=CV MOLE RATIO C=N/V OR V=N/C

Question 33

Explain why a substance is a reducing agent

Answer 33

The chemical loses electrons / gains oxygen / loses hydrogen, meaning that the chemical is being oxidised, therefore reducing another substance and therefore is a reducing agent.

Question 34

Explain why a substance is an oxidising agent

Answer 34

There is a gain of electrons/ loss of oxygen / gain of hydrogen, meaning that the substance is oxidising another substance and is being reduced therefore the substance is an oxidising agent.