Hydrated Iron 2 Sulphate Formula Essay Example

potassium permanganate as the titrant. Some of these chemicals are hazardous, H2SO4 is corrosive and KMnO4 is lethal if consumed in large enough doses. The full ionic equation for this titration is: MnO4-(aq) + 5Fe2+(aq) + 8H+(aq) ½ Mn2+(aq) + 5Fe3+(aq) + 4H2O(l). The potassium permanganate acts as a oxidising agent accepting electrons from the iron(II) which is oxidised to iron(III).

Results:

• Initial(cm3)0.022.33.60.0Final(cm3)22.344.
• 525.922.3Titre(cm3)22.322.
• 222.322.3Mass of FeSO4.nH2O used = 3.
• 05g.Average titre= (22.3+22.2+22.3+22.3)/4=22.275cm3.

Analysis:

With these results it is possible to calculate the amount of water from the mass of water obtained from the mass of hydrated iron(II) sulphate. To work out the amount of hydrated iron(II) sulphate the amount of potassium permanganate it reacts with needs to be known.

However, the anomaly is only off by 0.1cm3 and this would have a huge impact. Therefore the inaccurate answer must come from another factor. I think that the scales measuring only to the nearest hundredth of a gram produced only rough figures for the small scale titration that was carried out.

Scales with a greater resolution, or more realistically the experiment being carried out on a larger scale would reduce this error margin although this is only practical in laboratories and not schools. The good thing about method one is that there are less of these sums that can amplify errors and even though the same weighing scales were used the lack of sums with many decimal places reduces the error margin. This method generally relies on chemistry instead of maths and the only variable that could have caused the off answer was again the scales. Carrying out this experiment on a larger scale would be far too dangerous in

a school due to the use of fire.

The problem with method one being more in touch with chemistry is the risk of procedural errors. On heating the melanterite the substance changed in colour from blue to white indicating the water had been eliminated. However, there were also areas of dark red which indicate a further reaction. The heat was too strong and iron(III) oxide was formed with sulphur di- and trioxide: 2FeSO4(s)½ Fe2O3(s) + SO2(g) + SO3(g). These gases also escaped with the water and gave the impression that there was more water present as some sulphur and oxygen escaped as well. Heating the melanterite more gently and patiently for less time would make sure this didn't happen. If this didn't happen I am confident that this method would be more accurate than a titration as it is more purely chemistry instead of maths, which holds a greater chance of carrying errors over, despite my results suggesting otherwise.