[2} Figure 1: Equipment for the filtration
Experimentation:
Weigh out 0.5g of Potassium Sulphate on a weighing boat. The amount can range from 0.4-0.6g.
Transfer your weighed crystals into a 400cm3 beaker. To make sure that all the crystals have been transferred, wash the weighing boat with distilled water ensuring all crystals end up on the beaker.
Measure 150cm3 of 0.05HCl using a measuring cylinder and add this to the beaker contain the Potassium Sulphate.
Heat this solution using a Bunsen burner until it comes towards a boil. Keep stirring while adding 50cm3 of 0.1mol dm-3 BaCl2 solution.
Place a watch glass over the beaker and adjust the flame so that the solution can simmer for 15minutes.
Get a funnel and filter paper and fold the filter paper so it fits into the funnel. Using distilled water, wet the filter paper to hold it in place. Take a clean porcelain crucible and heat it over the Bunsen burner using tongs and leave it on a heat proof mat to cool.
As the BaSO4 crystals have cooled, pour the liquid through the filter. Take care as you do this. Do it slowly so that the solution level in the funnel is always below the top edge of the filter paper. When there is only a few cm3 solution remain in the beaker, swirl the precipitate and solution and pour quickly over the filter, Place the end of the stirring rod over the lip of the beaker and wash all of the precipitate from the beaker onto filter, allowing the washings to drain down the stirring rod.
Using distilled water, wash the precipitate on the filter two or three times with distilled water. Remember, the filtrate should be clear.
Fold the filter paper over by folding the edges so that the precipitate is enclosed in a small parcel. Remove it from the funnel and place it into the weighed crucible.
Using the Bunsen burner, place a clay triangle over it and mount the crucible containing the filter paper containing the precipitate. Turn the Bunsen flame down so the paper chars but remember, that you do NOT want it to burst into flames (otherwise some BaSO4 might be reduced to BaS). If the paper does burst into flame, burst a crucible cover momentarily over it to extinguish the flame.
Heat the crucible more strongly. Heat with full intensity of the burner for about 5 minutes. You should be left with a white ash of barium sulphate. Allow the crucible to cool and then weigh accurately.
Results:
Weight of sample of Potassium Sulphate taken for analysis:
Weight of empty weighing boat= 0.4466g
Weight of boat + K2SO4= 0.9020g
Weight of K2SO4= 0.4554g
Weight of Barium Sulphate produced:
Weight of empty crucible= 18.5091g
Weight of crucible + ash (BaSO4) = 18.8362g
Weight of BaSO4= 0.3271g
Calculation of the experimental percentage of the value of sulphate on Potassium Sulphate:
Moles= 1.04 x 10-3
To calculate the moles of Barium sulphate produced, you need to know the weight of Barium Sulphate and its molecular weight.
Weight of Barium Sulphate= 0.3721g
Molecular weight (MWt) of BaSO4 =(137.33 + 32.06 + (16x4))
= 233.39
Therefore moles can be calculate using the equation:
Moles= Mass/Molar Mass
Moles= 0.3271/233.39
= 1.04 x 10-4 (which is also the number of moles of SO42- in the crucible)
Calculate the weight if SO42- in the crucible from its molecular weight.
Weight of SO42-= 0.10g
In order to get the weight, you need to multiply the moles of SO42- and its molecular weight
Therefore:
Molecular weight = ((39.10x2) + 32.06 + (16x4))
= 96.06
=1.04 x 10-3 X 96.06
=0.10g
Experimental value for percent sulphate in Potassium Sulphate:
To get the percentage of SO42- you need to divide the weight of SO42- by the weight of K2SO4 and then multiply it by 100.
Weight of SO42-= 0.10g
Weight of K2SO4= 0.4554g
Therefore 0.10/0.4554 x 100
= 21.9%
Calculation of Purity of Potassium sulphate sample:
Expected percentage of SO42- in sample = 55%
To get the percentage purity, you need to divide the percentage of SO42- in the sample by the expected percentage of SO42- in the sample and then multiply it by 100. In this case that would be:
= 21.9/55 x 100
= 39.9%
Discussion:
In this discussion, it has shown that we have come to a conclusion that these results show that something during the experiment went wrong. Our expected percentage purity came out to be 39.9% whereas our expected percentage purity was 55%. This shows that this difference of 15.1%.
A few reasons as to why the experiment may have not been as accurate as hoped so could be because firstly the weight of the BaSO4 was not right as it only weighed 0.3714g. However, it should have been between 0.4g-0.6g. This may have been the main source of error. Secondly, as much as the precipitate was made to be sure that none was lost throughout the experiment, there may have been a slight but very small chance that some precipitate may have not been obtained. If that was true, than it may have affected the accuracy of the results.
The filter paper caught on fire slightly; this was only for a split second however it does contribute hugely to the fact that more precipitate many have been lost as some BaSO4 may have been reduced to BaS. In order to overcome this, the Bunsen burner could have been on an even lower heat.
Conclusion:
In conclusion, overall the experiment went quite well despite some accuracy flaws. However these can be overcome so that these flaws do not occur again. Apart from our huge percentage change, the experiment overall went well. What we found was that the calculation purity of Potassium Sulphate should have been around 55%; however, the value we obtained was 39.9%. The way in which this figure was obtained was by dividing the percentage of SO42- in the sample by the expected percentage of SO42- in the sample and then multiplying it by 100. Therefore overall you could argue that although percentage was found, it was not as accurate as it could have been.
References:
[1]
[2]
