Date: 3rd December, 2010

Name: Merish Farooq

Experiment no.3

Title: A redox Titration between Manganate (VII) and Iron (II)

Objective:

To determine the x in the formula Fe (NH4)2(SO4)2•xH2O by titration against a standard solution of potassium manganate (VII) (permanganate).

Theory:

The experiment involves a redox reaction between potassium manganate (VII) and ammonium

   

Potassium manganate (VII) is used in the experiment as it reacts completely and it is its own indicator. Potassium manganate (VII) solution is a strong oxidizing agent. In an acidic medium, manganate(VII) ion undergoes reduction as shown below.

               MnO4- (aq) + 8H+ (aq) + 5e- → 4H2O (l) + Mn2+ (aq)

Ammonium Iron (II) sulphate is a strong reducing agent because of the presence of Iron (II) ions. Iron (II) ions can be oxidized to form Fe3+ which is yellow in color.

Manganate (VII) ions are purple in color, when the MnO4- are reduced to Mn 2+, the color of the solution becomes pale pink, thus a self indicating titration can occur

According to the overall reaction:

               MnO4- (aq) + 5Fe 2+ (aq) +8H+(aq) → Mn2+(aq) +5Fe3+(aq)+4H2O(l)

                     

Between the titration of potassium manganate (VII) solution  and ammonium iron (II) sulphate solution, The molarity of ammonium iron (II)

Apparatus:

Safety spectacles

25cm3 pipette

Pipette filler

4 conical flasks

50cm3 burette

Small funnel

White tile

Wash-bottle of distilled water

Materials

Solution A: ammonium Iron(II) sulphate solution

1M dilute sulphuric acid

Solution B: potassium manganate (VII)

Procedures:

  1. The burette was filled with potassium manganate (VII) solution B
  2. 25 cm3of the ammonium iron (II) sulphate solution A into was pipette into a conical flask.
  3. 25 cm3of the dilute sulphuric acid was added into the conical flask filled with 25 cm3of ammonium iron (II) sulphate solution A
  4. The conical flask was titrated with potassium permanganate solution B
  5. The titration was stopped when a pale pink colour was formed in the conical flask
  6. The titration was repeated several times to obtain consistent results
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Result

Concentration of potassium manganate (VII) solution, B:  0.0189 ( mol dm3)

Concentration of ammonium iron (II) sulphate solution, A: 39.214 (g dm3)

 

Calculation:

                MnO4- (aq) + 5Fe 2+ (aq) +8H+(aq) → Mn2+(aq) +5Fe3+(aq)+4H2O(l)

We can find the no. of moles of MnO4- by:

                                                                        0.0189 × 26.05 ...

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In terms of spelling and punctuation, the essay was fine. There were a few moments in which the grammar could have been better; for example 'solution, The', there should not be a capital letter in the middle of a sentence. The structure of the essay was fine, however, it would have perhaps been better if the conclusion came before the questions, as then it links with their experiment a little better.

The student suggests understanding of the topic throughout the essay and clearly knows the theory behind the experiment well. The correct reaction equations are used and the calculations are all correct, with full working out, leading to the right answer/conclusion. It is good to include a discussion section, but this one is a little too brief. Specific examples for this candidate to improve could be to clearly define what a reducing/oxidising agent is to show understanding. They could also have talked more about possible experimental errors and how they worked to reduce them.

There is a clear aim in this piece of coursework, and the student has structured their essay in a logical order, going into suitable depth where necessary. The response to the question is good, they have given a brief introduction of the task and then gone through all the stages, methodically, to include all the information necessary to reach their conclusion and answer. The calculations section is all correct, however, it is very long to read and could have been broken down into several sections to make it easier to understand.