Oxidising and Reducing Agents

Oxidation

A reaction involving the loss of electrons

Reduction

A reaction involving the gain of electrons

Redox reactions

When oxidation and reduction happen simultaneously, electrons are transferred from the more reactive substance to the less reactive substance

Oxidising agents

A reagant which induces oxidation by accepting electrons An oxidising agent is therefore reduced in a redox reaction

Reducing agents

A reagant which induces reduction by donating electrons A reducing agent is therefore oxidised in a redox reaction

Electronegativity of oxidising agents

Oxidising agents need to accept electrons, so have high electronegativities to more successfully recieve electrons

Electronegativity of reducing agents

Reducing agents are oxidised so must be able to give electrons away more efficiently, so they have low electronegativites

Where are oxidising agents found in the ECS?

Oxidising agents are on the left side of the ECS, and are stronger towards the bottom

Where are reducing agents found on the ECS

Reducing agents are found on the right hand side of the ECS, and are strongest towards the top

Where are oxidising and reducing agents found in redox equations?

Oxidising and reducing agents are found on the reactant side of an equation, as they are reactant species

Steps to identify oxidising and reducing agents

Turn the redox equation into an ionic equation, and remove spectator ionsIdentify which substance gains electrons, this substance is reduced and is therefore an oxidising agentIdentify which substance loses electrons, this substance is oxidised and is therefore a reducing agent

What trends allow you to identify oxidising and reducing agents?

ECS positioning, electronegativity, and common agents

Hydrogen Peroxide, H2O2, is a ....

Hydrogen Peroxide is a common oxidising agent

What are the uses of H2O2?

Hydrogen peroxide is used as a bleaching agent for hair and clothes It is also used as an agent in cleaning products that kills bacteria

Dichromate, Cr2O72-, is a...

Dichromate is a common oxidising agent

In order to be an oxidising agent, dichromate ions must be...

In order to be an oxidising agent, dichromate ions must be under acidic conditions

Uses of dichromate ions

Used to oxidise alcoholsUsed in the old-fashioned development of photographs

Permanganate, MnO4-, is a...

Permanganate is a commo oxidising agent

To be an oxidising agent, permanganate ions must be...

To be an oxidising agent, permanganate ions must be must be under acidic conditions

What are the uses of permanganate ions?

Potassium Permanganate solution is used to bleach jeansPotassium Permanganate used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial/fungal infections

"What does ""under acidic conditions"" mean?"

H+ ions must be supplied to a reaction

What is a self-indicating reaction?

A reaction that shows signs when the endpoint is reached, such as colour change

How is Potassium Permanganate self-indicating?

It goes from purple to colourless

How is Potassium Dichromate self-indicating?

It goes from orange to green

What are the general uses of oxidising agents?

Uses to kill bacteria and fungi, can inactivate virusesOxidation process is is effective at breaking down compounds, so oxidising agents are used as bleachesFireworks use oxidising agents to produce the oxygen needed to burn the explosive compound inside

Carbon monoxide, CO, is a...

Carbon monoxide is a common reducing agent

As a reducing agent, wha are the uses of CO?

Widely used in blast furnacesCO reduces iron ions from iron ore (Fe2+ and Fe3+) to iron metal

What are the general uses of reducing agents?

Used to extract metals less reactive than Alminium from their ores

Simple ion-electron equations

Oxidation or reduction equations that only involve one type of element

How do you balance simple ion-electron equations?

Balance the charge on both sides of the equation by adding electrons

What are complex ion-electron equations?

Oxidation or reduction equations which involve molecules or group ions

How do you balance complex ion-electron equations?

Balance all non hydrogen or oxygen elements Balance the oxygen by adding the appropriate number of water molecules to one side of the equationBalance the hydrogen by adding the appropriate number of hydrogen ions to one side of the equation (NOTE: because of dissociation of water, H2O can't exist on the same side as H+ or OH-)Balance the charges by adding the appropriate number of electrons to one side of the equation

What are redox equations?

The transfer of electrons, where one element is oxidised and one is reduced at the same time

How do you balance redox equations?

Find relevant ion-electron equations (make sure to flip the more reactive equation as this is oxidation)Balance the electrons on both equationsCancel out electrons and other molecules Merge the equations

How do you find an ion-electron equation from a redox equation?

Identify either the reduction or oxidation equation and cancel it out from the redox equationBalance the remaining ion-electron equation to have both reduction and oxidation

Volumetric analysis

Using a solution of accurately known concentration in a quantitative reaction to determine the concentration of another substance

Standard solution

A solution of accurately known concentration

How do you prepare a standard solution?

Measure an accurate mass of solute, and add it to a beakerDissolve the solute in a small amount of deionised water and add to a volumetric flaskRinse the beaker multiple times with deionised water and add to the volumetric flask until the solution is made up to the mark Mix the solution when in the volumetric flask to evenly distribute concentration

Volumetric flask

A flask used to measure a specific volume of solution

Burette

A piece of equiptment which drops solution from the nozzle, typically holds the standard solution in a titration

Pipette

Used to measure an accurate volume of solution

Balance

Used to measure an accurate mass

Indicator

Used to determine the endpoint of a reaction, some reactions are self-indicating and don't require additional substance to determine the endpoint

Setup for a titration

When filling the burette with standard solution, use a funnel and waste beaker (in case of drip) and fill to above the mark; then slowly release until the bottom of the miniscus touches the mark (remove funnel to keep the level the same)When filling the conical flask, use a pipette to measure an accurate volume and fill to above the line; then slowly release until the bottom of the miniscus touches the markUse a white tile under the conical flask to better see the endpoint

To prepare an accurately known concentration of solution, use a...

To prepare an accurately known concentration of solution, use a volumetric flask

Titres

The volume of standard solution added to a solution of unknown concentration to reach the endpoint

Concordant titres

Titres within 0.2cm3 of one another, the average volume of standard solution is calculated from concordant titres

Rough titre

Used to get a rough idea of how much standard solution to add during proper titrations, never used as a concordant titre

What do you rinse the a. conical flask (between titrations), b. burette, and c.pipette with?

a. water (but make sure the conical flask is dry before carrying out titrations so you don't affect concentration b. standard solution c. solution of unknown concentration

What is good practice when carrying out a titration?

Fill to above the line in the burette and pipette then release solution until the bottom of the miniscus reaches the markRead at eye levelUses a white piece of paper behind scale to read it better, and use a white tile to determine the endpoint better