(CHEM) Topic 9 - Oxidation and reduction

OXIDATION definition

An increase in oxidation state

REDUCTION definition

A decrease in oxidation state

Which side of an oxidation half-equation is the electron on?

Right

Which side of a reduction half-equation is the electron on?

Left

Typical oxidation state of H

+1

Typical oxidation state of O

-2

What when is there an exception in oxidation state of H?

-1 in metal hydrides

What when is there an exception in oxidation state of O?

-1 in peroxides

REDOX REACTION definition

Change in oxidation state in acidified conditions

What determines the oxidation number (eg.: (II) )?

The oxidation state of the preceeding transition metal

DISPROPORTION definition

A redox reaction in which the same element is both oxidised and reduced

Color change of pottasium dichromate Cr₂O₇^2- when oxidises

Orange to green

Product of the oxidation of a primary alcohol

Aldehyde

Product of the oxidation of a secondary alcohol

Ketone

Product of the oxidation of an aldehyde

Carboxylic acid

Product of the oxidation of a tertiary alcohol

Tertiary alcohols DO NOT oxidise

Method of oxidising aldehydes

Heating under reflux (with excess oxidising agent)

Method of oxidising secondary alcohols

Heating under reflux (with excess oxidising agent)

Method of oxidising primary alcohols

Distillation

While balancing a redox equation, what should be balanced first?

Number of important atoms (all except H and O)

Arrange the following steps in the correct order for balancing a redox equation: balancing charges, #O, #H, # important atoms

• Number of important atoms

• Number of oxygen atoms

• Number of hydrogen atoms

• Charges

What metals are the best reducing agents?

Most reactive metals (Fe)

What non-metals are the best oxidation agents?

Most reactive non-metals (F)

At which electrode does oxidation occur?

Anode

At which electrode does reduction occur?

Cathode

Function of the salt bridge in a voltaic cell

Allows ion flow between two half-cells and prevents buildup of charge

In a (grahite) carbon-zinc dry cell, which is the anode and which is the cathode?

Zinc anode, graphite cathode

Which species goes first on a cell diagram?

The species being oxidised

Which direction do electrons flow in a voltaic cell?

From anode to cathode

Which direction do electrons flow in an electrolytic cell (including the power cell)?

From anode to power cell to cathode

What direction do electrons flow in (in terms of +/-)?

- to +

A primary voltaic cell converts … energy to … energy

Chemical to electrical

An electrolytic cell converts … energy to … energy

Electrical to chemical

Which is spontaneous: a volatic cell or an electrolytic cell?

A voltaic cell

Which requires a power source: a voltaic cell or an electrolytic cell?

An electrolytic cell

The reactions in a voltaic cell are (exo/endothermic)

Exothermic

The reactions in an electrolytic cell are (exo/endothermic)

Endothermic

The anode in a voltaic cell is …

Negative

The cathode in a voltaic cell is …

Positive

The anode in an electrolytic cell is …

Positive

The cathode in an eletrolytic cell is …

Negative

What is the liquid in an electrolytic cell?

Molten electrolyte

What are the electrodes in an electrolytic cell made of?

Unreactive metals

An example of a secondary voltaic cell

Lead-acid car battery

An example of a primary voltaic cell

Carbon-zinc dry cell

When does the reverse redox reaction take place in a secondary voltaic cell?

During recharging

3 cons of a secondary voltaic cell

• Distilled water needs to be added

• Heavy

• Polluting

2 pros of a secindary voltaic cell

• Reusable

• High power density

Which is rechargabe: primary voltaic cell, secondary volatic cell, electrolytic cell or fuel cell?

Secondary voltaic cell

Reactants in a fuel cell

Hydrogen and oxygen

A fuel cell generates energy by …

Combustion of hydrogen

2 pros of a fuel cell

• Enery efficient

• Environmnetally friendly

2 cons of a fuel cell

• Expensive

• Needs continuous supply of reactants