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The mineral iron pyrite (FeS2), typically, has a mass percentage of what is known as fool’s gold of 90-95%. The actual percentage in a sample can be determined using gravimetric analysis.
To find the % mass of FeS2 the sulphur in FeS2 is firstly converted to sulphate (SO42-). These sulphate ions (SO42-) is mixed with an excess of barium chloride (BaCl2) to form barium sulphate (BaSO4), according to the following reaction:
Ba2+(aq) + SO42- (aq) à BaSO4 (s)
When the reaction has gone to completion, the BaSO4 precipitate is collected in a filter paper and carefully washed. The filter paper and its contents are then transferred to a crucible. The crucible and its contents are heated until constant mass is achieved.
The data for the analysis of a mineral sample is shown in the table below:
|
Initial Mass of mineral sample |
17.5 g |
|
Mass of crucible and filter paper |
144.60 g |
|
Mass of crucible, filter paper and dry BaSO4 |
196.89 g |
|
Molar mass FeS2 |
120.0 g/mol |
|
Molar mass BaCl2 |
208.3 g/mol |
|
Molar mass BaSO4 |
233.4 g/mol |
Using this information available in the table, calculate the percentage by mass of iron pyrite FeS2 in this mineral sample, by answering the following questions:
(a) Balance the following reactions:
2 FeS2 + H2SO4 → Fe2(SO4)3 + SO2 + H2O (Reaction 1)
Fe2(SO4)3 + BaCl2 → BaSO4 + FeCl3 (Reaction 2)
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(b) Find the mass of barium sulphate (BaSO4) from the data given in the table.
(c) Calculate the moles of barium sulphate (BaSO4)
(d) Using stoichiometry for the balanced reactions, Reaction 1 and Reaction 2 from part (a), find the moles of FeS2
(e) Calculate the theoretical mass of FeS2 using your answer for moles FeS2 in part (d)
(f) Calculate % mass iron pyrite FeS2 using the theoretical mass and the initial mass of mineral sample. How does your calculated % mass iron pyrite FeS2 compare to the typical 90-95% mass?
(b) Find the mass of barium sulphate (BaSO4) from the data given in the table.
(c) Calculate the moles of barium sulphate (BaSO4)
(d) Using stoichiometry for the balanced reactions, Reaction 1 and Reaction 2 from part (a), find the moles of FeS2
(e) Calculate the theoretical mass of FeS2 using your answer for moles FeS2 in part (d)
(f) Calculate % mass iron pyrite FeS2 using the theoretical mass and the initial mass of mineral sample. How does your calculated % mass iron pyrite FeS2 compare to the typical 90-95% mass?
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