D. Results
Some shiny light-green crystals of Iron (II) Sulphate (FeSO4) are obtained along with some small brown particles and dust. Total weight of crystals of Iron (II) Sulphate (FeSO4) is 4.3 gram
The percentage yield of the salt:
The number of mol of Sulphuric acid (H2SO4) used:
40ml x 1mol/dm3 = 0.040dm3 x 1mol/dm3 = 0.040 mol
The reacting equation can be represented as
Fe + H2SO4 → FeSO4 + H2
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From the equation, 1 mol of Sulphuric acid reacts totally with excess Iron fillings (Fe) to form 1 mol of Iron (II) Sulphate (FeSO4)
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Therefore, the expected amount of Iron (II) Sulphate (FeSO4) formed when using 0.040 mol of Sulphuric acid (H2SO4) is 0.040 mol which means the expected amount if crystal is also 0.040 mol
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The weight of the expected amount of Iron (II) Sulphate crystal (FeSO4) is:
0.040mol x (56 + 32 + 16x4)g/mol = 6.08g
E. Evaluation and Conclusion
Evaluation of the experiment:
- The synthesis was done with care taken when cleaning all the apparatus and carrying out all the transferring. This is to minimize the impure particles in the solution before let it evaporate and get the highest purity of the crystals.
- Using the evaporating dish ensures that the crystals will be formed in a short amount of time compared to the plastic bottle.
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The yield is calculated to be less than 100% due to various reasons. First, it is the loss of a certain amount of solution in every transferring (i.e. from the beaker to the funnel, from the funnel to the dish). Second, some crystals are overheated until anhydrate, resulting in turning into powder, which was not to be weighted. Finally, the small part of the solution of Iron (II) Sulphate (FeSO4) has been oxidized to Iron (III) Sulphate, Fe2(SO4)3.
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When the crystal is supposed to be transparent and shiny, the obtained crystals have some tiny milky white areas and some brown dots on its surface. The tiny milky white areas were formed because the crystals were put too long under the IR light when drying up. Water from the surface of the crystal evaporated, leaving off the surface of anhydrous Iron (II) Sulphate (FeSO4) milky white areas. The brown dots are crystals of Iron (III) Sulphate, Fe2(SO4)3, which is formed when Iron (II) Sulphate (FeSO4) was oxidized.
Improvement can be made
- Shortening time taken to evaporate the solution:
- Heat up the solution (refer to step 7) until some white powder appears at the wall of the evaporating dish, take the dish down immediately.
- Pour the solution into evaporating dish
- Cool down solution, i.e. let it still for about 1 day
- Place the evaporating dish under the IR light for about 30-35 minutes
- Take out, continue letting it evaporate naturally. For about 1 day later, we will find out some nice formed crystals appear at the bottom of the bottle
Advantages of this modification:
- It shortens time taken to evaporate the solution since the solution after cooled down is put under IR light, with the heat from the light the evaporation occurs faster.
- Avoid over heat when heating the solution.
- Another way to store the solution when waiting for it to evaporate the water
Instead of using evaporating dish, we can also use a plastic bottle to store the solution
Advantage: using the plastic bottle gives out large size and well-formed crystal; while the evaporating dish, due to its large surface area, the solution spreads over on a large area and therefore the crystals obtained at last is most likely in a form of tiny rods.
Limitation: this will obviously takes a longer time to get the desired product.
F. Acknowledgements
First and foremost, to my subject teacher, Ms. Angeline Chua, for her detailed and carefully prepared instruction.
I cannot fully express my gratitude to the lab assistances for their generous assistance whenever I had any problems with my project
For his tireless support in doing the project, I would like to acknowledge Le Viet Anh of class 4.17 Solomon.
G. Bibliography
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Rex M Heyworth, J G R Briggs, Chemistry Insights 2nd edition, Pearson Longman, 2007
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Anglo-Chinese School (Independent), Hand-out Year 3 IP Chemistry, Salt Preparation Report Format, 2008
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Wikipedia©, “Iron(II) Sulphate”, http://en.wikipedia.org/wiki/Iron%28II%29_Sulphate
