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# A2 Chemistry -Assessed Practical In theory the remaining mass after the heating will be only FeSO4, so from this the mass that was evaporated off would be entirely water. From this we can calculate

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Introduction

A2 Chemistry - Assessed Practical Method 1 Mass (g) Total Mass Loss (g) Original Mass 1.44 0.00 Measurement 1 1.05 0.39 Measurement 2 0.90 0.54 Measurement 3 0.88 0.56 Measurement 4 0.86 0.58 Measurement 5 0.86 0.58 Calculations In theory the remaining mass after the heating will be only FeSO4, so from this the mass that was evaporated off would be entirely water. From this we can calculate: The number of moles of H2O is the n= m/Mr H=1 O=16 H2O = 18 =Mr 0.58/18 = 0.032 moles of H2O The remaining mass should be entirely FeSO4 so: Fe=56 S=32 O=16 56 + 32 + (4x16) = 152 = Mr The number of moles of FeSO4 = 0.86/152 = 5.657894737 x 10^-3 Moles To find the ratio of H2O we need to use: 0.032/5.657894737 x 10^-3 = 5.655813953 This is approximately 6 so the Formula of the Hydrated Iron (II) ...read more.

Middle

Using Mr = n/m 3.08 / 0.01103125 = 279.2067989 Then take away the Mr of FeSO4 gives the amount of water in the compound 279.2067989 - 152 = 127.2067989 Then divide by the Mr of water to get how many are in the original compound 127.2067989 / 18 = 7.067044381 So the formula of the compound is FeSO4.7H2O Evaluation Measurement Errors One of the largest measurement errors is in the weighing of the compound. The scales used only weigh to 2 decimal places. For a titration this is not accurate enough as the titration can precise. The preferable accuracy would be to at least 3 decimal places as the lack of accuracy could greatly affect the results of the calculations. Also in Method 1 we do not know whether or not there was any absorption of moisture during the cooling period. This can be a large problem as the method relies on the fact that the reaction no longer takes place when there is no more water. ...read more.

Conclusion

This may still be inaccurate as the steam given off will also be trapped within the burette. To avoid this it could travel through a condenser first in order to extract the steam from other products. With this the total mass of the compound could be found and calculations could be accurate enough to calculate the amount of H2O in the formula. There is also a problem in not knowing when the reaction is finished except by measuring the compound every so often to find when the mass no longer changes. A more accurate set of scales would help with this problem as we could check for when the mass of the compound stops changing by such large amounts, so that we could assume it was the compound that was now thermally decomposing. These errors are mainly to do with Method 1 and so I would again recommend Method 2 as there are far fewer inaccuracies and procedural errors. The only problem factor in Method 2 is human and unpredictable. ?? ?? ?? ?? Jonathon Higham ...read more.

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