Unit 1 - Oxidising and Reducing Agents

Question 1

Oxidation

Answer 1

Oxidation is a loss of electrons by a reactant in any reaction.

Zn(S) –> Zn2+(aq) + 2e-

Question 2

Reduction

Answer 2

Reduction is a gain of electrons by a reactant in any reaction.

Cu2+(aq) + 2e- –> Cu(s)

Question 3

Redox

Answer 3

In a redox reaction, reduction and oxidation take place at the same time.

Zn(s) +Cu2+ (aq) –> Zn2=(aq) + Cu(s)

Question 4

Oxidising Agent

Answer 4

An oxidising agent acts on another substance to oxidise it. An oxidising agent accepts electrons (so is therefore reduced).

Question 5

Reducing Agent

Answer 5

A reducing agents acts on another substance to reduce it. A reducing agent donates electrons (so is therefore oxidised).

Question 6

Redox and Electrochemical Cells

Answer 6

In an electrochemical cell, electrons in wires will always travel from the reducing agent (electron donor) to the oxiding agent (electron acceptor).

Question 7

Elements - Metals

Answer 7

Elements with low electronegativities (metals) form positive ions by losing electrons (oxidation) and so can act as reducing agents. In the periodic table, the strongest reducing agents are in group 1.
In the Electrochemical Series, the strongest reducing agents are at the top of the right-hand colum, Lithium (Li) is the most effect reducing agents.

Question 8

Elements - Non-metals

Answer 8

The elements with high electronegativities (non-metals) form negative ions by gaining electrons (reduction) and so can act as oxidising agents. In the periodic table, the strongest oxidising agents are in group 7.
In the Electrochemical Series, the strongest oxidisng agents are at the bottom of the left-hadn column. Fluorine (F2) is the most effective oxidising agent.

Question 9

Compounds and Group Ions

Answer 9

Compounds and group ions can also act as oxidisng and reducing agents.
* Hydrogen peroxide (H2O2) is a strong oxidising agent.
* Dichromate (Cr2O7 2-) and premanganate (MnO4 -) ions are strong oxidising agents in acidic solutions.
* Carbon monoxide (CO) is a gas that can be used as a reducing agent.
* Sulfite ion in solution (SO3 2-(aq)) is a useful reducing agent.

Question 10

Uses of Oxidising Agents

Answer 10

Oxidising agents are widely used because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses.
The oxidation process is also an effective means of breaking down coloured compounds, making oxidising agents ideal for use as ‘bleach for clothes and hair.

Question 11

Uses of Oxidising Agents -
Potassium premanganate (KMnO4)

Answer 11

• As a disfectant
• To treat athelete’s foot
• To extend the shelf life of fruit and vegetables (by reacting with ethene gas which causes ripening)

Question 12

Uses of Oxidising Agents -
Bleach (sodium hypochlorite solution NaOCl)

Answer 12

• As a disfectant
• To remove stains

Question 13

Uses of Oxidising Agents -
Hydrogen peroxide (H2O2)

Answer 13

• To whiten paper
• For teeth whitening
• For hair ‘bleaching’

Question 14

Balancing Ion-Electron Equations

Answer 14

Step 1 - start with given ions
Step 2 - balance non-oxygen symbols (i.e chromium)
Step 3 - balance oxygen symbols with water molecules
Step 4 - balance hydrogen symbols with hydrogen ions
Step 5 - balance charges with electrons

Tip - electrons are added to the more positive side