LC CHEMISTRY- REDOX TITRATION 1- AN AMMONIUM IRON (II) SULFATE / POTASSIUM MANGANATE (VII) TITRATION

Redox Titrations

Titrations involving oxidising and reducing agents

Oxidising Agent

potassium permanganate (KMnO4)

Reducing Agent

ammonium iron (II) sulfate (NH4)2SO4.Fe(SO4).6H2O

Potassium Manganate (VII) is___

not stable, not pure, dark purple

Ammonium iron (II) sulfate is___

Stable, solid, high molecular mass

Ratio

1 MnO4^- : 5Fe^2+

(a) Is used to standardise (b)

(a) Ammonium Iron (II) Sulfate ((NH4)2SO4.Fe(SO4).6H2O) (b) Potassium Permanganate (KMnO4)

Molarity of Potassium Manganate (VII) used

0.02M

How many times do we add dilute H2SO4 (Sulfuric Acid)

twice

Explain why its necessary to use dilute sulfuric acid when preparing the standard solution from hydrated ammonium iron (II) sulfate

To prevent the oxidation of the Fe^2+

Explain why its necessary to add more dilute sulfuric acid to each 25.0 cm³ portion of the standard solution used in the titrations

To ensure Mn (VII) reduces to form colourless Mn (II)

What happens if we get the brown participate of Mn(IV)

add more sulfuric acid

end point colour change

colourless to permanent pale pink

indicator

potassium permanganate

standard solution

known concentration (molarity)

3 essential properties of standard solution

pure, soluble,solid

give 3 other procedures used on the conical flask to ensure the accuracy of the end point

swirling the conical flask , carry out a rough titration, rising down the walls of the conical flask with deionised water

describe how you would prepare 250cm^3 of a standard solution of x G of (NH4)2SO4.FeSO4.6H20 - Hydrates ammonium iron (II) sulfate that was supplied on a clock glass

Add rinsings of clock glass to beaker, dissolve in beaker containing dilute sulfuric acid

if insufficient acid was present in the conical flask what would have been observed as the KMnO4 solution was added from the burette to the Fe^2+ ion solution, Explain

Brown precipitate (Solid) Mn(IV) formed

How could you ensure that all the solution was transferred from the small beaker to the volumetric flask -3 points-

rince beaker several times, with small quantities of deionised water, and add rinsings into volumetric flask

Describe the procedure for washing and filling a burette with the potassium manganate(VII) solution -4 points-

rinse with deionised water, rinse with potassium permanganate, clamp vertical, and use funnel to fill

Describe fully the procedure used during the titrations to ensure the accuracy of the end point -5 points-

swirl flask while adding potassium permanganate, rinse down the side of the walls of the conical flask with deionised water, keep burette vertical, read at the top of the meniscus, carry out rough titration

Name the piece of equipment that should be used to transfer the 25cm^3 of ammonium iron (II) sulfate to the conical flask

pipette

Describe the correct procedure for rinsing this piece of equipment and transferring the solution to the conical flask -9 marks-

Rinse once with deionised water and once with the solution it will contain, Fill pipette to mark with pipette filler, To ensure full delivery hold tip of pipette against side of conical flask

What colour change would you observe as the solution from the burette flows into the conical flask

intially purple and gradually goes colourless then the endpoint is colourless to permanent pale pink

the role of the Mn^2+ produced in this reaction

Acts as an auto catalyst. Causes the decolouration to speed up after each addition

explain why nitric acid could not be used to provide acidic conditions for this reaction

strong oxidising agent