PK - Redox Chemistry and Titrations

What does the suffix “ic“ indicate?

Acids with higher proportion of oxygen than those with the “ous“ ending

e.g sulfuric acid compared to sulforous acid.

What is redox Chemistry

Reaction in which electrons are transferred between the reactants

What are the rules based on electronegative arguments?

1. All elements, in elemental state have an oxidation state of 0.

2. The sum of oxidation states in a molecule or ion is equal to the charge on the molecule or ion.

3. F has an ox state of -1 in all its compounds

4. H has an ox state of +1 in all its compounds except metal hydrides where it is -1

5. O has an oxidation state of -2 in all compounds except peroxides (o2 = 2-) and super oxides (02 -1) and OF.

6. Na and K have OS = +1 in all their compounds

What is an oxidising agent?

A species that accepts electrons and is therefore reduced in the process.

What is a reducing agent?

Species that donates electrons and is therefore oxidised in the process.

Define disproportionation

A reaction where a species is both oxidised and reduced simultaneously.

What are the 4 clear requirements for titrations?

1. Reaction should be fast

2. Reaction must go to completion

3. Stoichiometry must be precisely defined

4. End point must be sharply defined.

Define equivalence point

The point at which the theoretical amount (stoichiometric amount) of titrant has been added.

Define end point

Experimental estimate of the equivalence point.

What problem arises when using potassium permanganate?

• A standard can’t be prepared by weighing out KMnO4 and making up a solution in a volumetric flask because of the difficulty in having pure material.

• Insoluble MnO3 can be present in the solid and can form in solutions that have been stored for a while.

• Although both have minor effects, the precision is affected therefore titration will not be accurate therefore, KMnO4 must be standardised.

Four key points about primary standards

1. Need to be stable, both in the long term storage of the solid and in the solutions when made up.

2. Need to be readily (i.e cheaply) made in high purity form.

3. Shouldn’t take up water when stored - affects number of moles.

4. Should have a high “equivalent weight“ i.e. reactive component should be a small part of the big molecular weight system - reduces errors due to weighing

Define comproportionation

i.e the opposite of disproportionation

Two different oxidation states come together to give a product with just one.

Define indirect titration

One where the analyte is not itself involved in the titration but is used to generate or remove the reagent which is titrated.

What is a complexometric titration?

Generally used for the determination of metal ions in solution