Applied Science BTEC Nationals/Chemical Laboratory Techniques/Iron tablet
To Investigate The Percentage Of Iron In “Iron Tablets.”[edit | edit source]
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Discussion.[edit | edit source]
Iron tablets are prescribed for anaemia. The iron in commercial iron tablets is in the form of Fe2+. This can be oxidised to Fe3+ by the manganate (VII) ('permanganate') ion. This is the reaction which will form the basis of our titration.
MnO4- + 8 H+ + 5 e- → Mn2+ + 4 H2O
Fe2+ → Fe3+ + e-
5 Fe2+ + MnO4- + 8 H+ → 5 Fe3+ + Mn2+ + 4 H2O
First we need to prepare a standard solution of sodium ethanedioate and titrate it with the given potassium manganate (VII) solution to determine the concentration of the manganate (VII) solution
Apparatus[edit | edit source]
beakers, 250 cm3
burettes, 50 cm3
measuring cylinder, 25 cm3
pipettes, 25 cm3
volumetric flasks, 250 cm3
Bunsen burner, tripod & gauze
conical flasks, 250 cm3
Reagents[edit | edit source]
potassium manganate (VII) solution
Precautions[edit | edit source]
Wear eye protection and laboratory coat at all times. Tie back long hair when using Bunsen burners.
Standard Solutions Procedure.[edit | edit source]
- 1. Weigh out accurately 1.65 - 1.70 g of sodium ethanedioate Na2C2O4 into a 250 cm3 beaker by the following procedure:
- a) Place a weighing bottle on the top-pan balance and tare the balance.
- b) Add the required quantity of salt.
- c) Now weigh the bottle plus salt on an analytical balance, tip the salt into the beaker and weigh the bottle "empty."
- 2. Add about 100 cm3 de-ionised water and stir the mixture to dissolve the solid. Transfer this solution to a 250 cm3 volumetric flask and make up to the mark with de-ionised water, observing all the normal precautions for making up a standard solution.
- 3. Pipette 25cm3 aliquots into a 250 cm3 conical flask and add about 25 cm3 dilute sulphuric acid.
- 4. Heat the mixture to about 70 °C and titrate with manganate (VII) solution until a faint permanent pink colouration is obtained.
- 5. Repeat twice more to obtain accurate titrations.
Calculations[edit | edit source]
- 1. Use your weighings to determine the mass of sodium ethanedioate used to make up the solution and hence determine its concentration.
- 2. The fully balanced equation for the standardisation titration is:
5 C2O42- + 2 MnO4- + 16 H+ → 10 CO2 + 2 Mn2+ + 8 H2O
- Use this equation to determine the concentration of the manganate (VII) solution used in this experiment.
Questions[edit | edit source]
- Suggest a reason why the titration flask is heated to 70 °C before the titration is carried out.
- Write out the half ionic equations for the reactions and identify, giving your reasons, the oxidising and reducing agents.
- This particular reaction is said to proceed by a process of "autocatalysis". Explain what this term means.
Iron Tablet Analysis Procedure.[edit | edit source]
- Accurately note the mass of one iron tablet.
- Crush this tablet to a fine powder in a mortar with a pestle.
- Rinse all of the crushed tablet into a conical flask and add about 25 cm3 of dilute sulphuric acid. Add more water and / or warm if you experience difficulty in getting the tablet to dissolve completely.
- Titrate this solution with the standard potassium manganate (VII) solution in as accurate a manner as possible until a pink colour is obtained.
- From your result, decide if have obtained a suitable titre. Do you need to use more than one tablet or use a dilute solution as the equivalent of using less than one tablet?
- Repeat the titration accurately in the chosen manner.
- For each titration, calculate the mass of iron in one tablet.
- Calculate the percentage mass of iron in a tablet
- Compare your values with other members of the group and find average values.
Questions.[edit | edit source]
- Compare and contrast this technique with that used in the previous titrations. Consider carefully the sources of errors and mistakes in the two techniques.
- Describe briefly how this experiment would be used in an industrial or commercial context.