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Gravimetric Analysis |
Experiment 1 Online Tutorial >> Gravimetric Analysis >> Step 2: Tutor 2
Experiment 1 - Gravimetric AnalysisStep 2: Calculating the amount of 0.35 M Na2SO4 solution to addIn step 2, we need to add enough SO42- to precipitate all of the Pb2+ ion in the solution as PbSO4. The amount of Pb2+ in the solution is not known at this point, but we can ensure that we add enough by considering the case in which all of the solid is Pb2+. In this way, we can ensure that we have added a sufficient amount. Any extra SO42- simply remains in solution above the solid PbSO4 and so does not interfere with the remainder of the analysis. Our goal is to determine the amount of 0.35 M Na2SO4 solution to add. Suppose the original sample weighs about 0.8 g. Assuming that the entire sample is lead, calculate the volume of 0.35M Na2SO4 solution (in milliliters) you would need to completely precipitate the lead ions?
(Please give your answer to 2 significant figures)
Hint
mL
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Hint:
If you are having trouble, scroll below to get step by step help in solving this problem.
The following tutors are a step by step walkthrough that show the details on how to solve the above problem. The formation of the solid PbSO4 is an example of reaction stoichiometry, for which we need a balanced chemical equation. What is the balanced chemical equation for this reaction?
Hint
Select
1
2
4
Pb2+(aq)
+
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1
2
4
SO42-(aq)
->
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1
2
4
PbSO4(s)
Based on the balanced reaction above, what is the relationship between the moles of sulfate consumed and moles of lead consumed?
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1
2
4
mole(s) of
SO42- consumed for each 1 mole of
Pb2+
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Hint:
To balance the number of Pb2+ ions in the reaction, start by entering 1.
Hint:
To balance the number of sulfate ions in the reaction, start by entering 1.
Hint:
Because there is 1 atom of Pb on the left and 1 sulfate ion on the left, enter 1 to balance the products with reactants in the reaction.
Hint:
Based upon the balanced equation, 1 mole sulfate is consumed for each 1 mole of Pb2+ consumed.
Our next task is to determine the number of moles present if we assume that the entire sample is lead. How many moles are there in 0.8 g of Pb? (Note: the atomic weight of Pb is 207.2 g/mol)
Hint
moles Pb
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Hint:
How do you convert from grams of Pb to moles of Pb?
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Hint:
To convert from grams to moles, use the atomic weight of Pb (207.2 g/mol).
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Hint:
Assuming the sample is 100% Pb, the result is:
(0.8 g Pb / 207.2 g mol-1 Pb) = 0.003861 moles Pb. get previous hint
How many moles of sulfate ion are required to react with the calculated number of Pb in our 0.8 g sample?
Hint
moles SO42-
What is the relationship between moles of sulfate ion and moles of Na2SO4?
1 mole of Na2SO4 produces
Select
1
2
4
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That's not quite right.
Hint:
From the balanced chemical equation, we see that 1 mole of sulfate ion is required to react with each 1 mole of Pb2+.
Using this 1:1 ratio, can you determine how many moles of SO42-
are required?
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Hint:
0.003861 moles Pb * (1 mole SO42- consumed) / (1 mole Pb2+ consumed)
= 0.003861 moles SO42-. get previous hint
Hint:
One SO42- ion is present in each Na2SO4 molecule
Our last step is to convert the moles of sodium sulfate calculated above to volume required. How many mL of a 0.35M Na2SO4 solution are required to react with the 0.8 g sample?
Hint
mL of 0.35M Na2SO4
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That's not quite right.
Hint:
To convert from moles of sulfate to mL of sulfate, use the molarity of sodium sulfate, Na2SO4 (0.35M). What are the units of molarity (M)?
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Hint:
Molarity = moles/volume in L so volume (in L) = mol / M. Using this conversion, how many mL are required?
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Hint:
The result is: 0.003861 moles/0.35 M Na2SO4 = 0.01103 L = 11.03 mL.
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| Last Updated: Sunday, November 13th, 2022 @ 07:12:28 pm |