The formula of a compound of lead (Pb) and sulfur (S) was determined using the method in this module. A sample of Pb was weighed into a crucible and covered with finely powdered S. The crucible was covered and heated to allow the Pb and S to react. Additional heating burned off all unreacted S. The crucible was then cooled and weighed. The following data were collected.
Mass of crucible and cover, g (27.889)
Mass of crucible, cover, and Pb, g (32.025)
Mass of crucible, cover, and compound formed, g (32.666)
1) Calculate the mass of Pb reacted.
2) Calculate the mass of compound that formed.
3) Calculate the mass of S reacted.
4) Calculate the number of moles of Pb reacted.
5) Calculate the number of moles of S reacted.
6) Find the simplest whole-number ratio of the number of moles of Pb to the number of moles of S in the compound formed.
7) Write the empirical formula for the compound formed.
These should help.
https://socratic.org/questions/how-can-i-calculate-the-empirical-formula-of-magnesium-oxide
http://www.webassign.net/userimages/fgdennis@waynecc/Lab_MgO_Intro.pdf
1) To calculate the mass of Pb reacted, we need to subtract the mass of the crucible and cover from the mass of the crucible, cover, and Pb.
Mass of Pb reacted = Mass of crucible, cover, and Pb - Mass of crucible and cover
Mass of Pb reacted = 32.025 g - 27.889 g
Mass of Pb reacted ≈ 4.136 g
2) To calculate the mass of the compound that formed, we need to subtract the mass of the crucible and cover from the mass of the crucible, cover, and compound formed.
Mass of compound formed = Mass of crucible, cover, and compound formed - Mass of crucible and cover
Mass of compound formed = 32.666 g - 27.889 g
Mass of compound formed ≈ 4.777 g
3) To calculate the mass of S reacted, we need to subtract the mass of Pb reacted from the mass of the compound that formed.
Mass of S reacted = Mass of compound formed - Mass of Pb reacted
Mass of S reacted = 4.777 g - 4.136 g
Mass of S reacted ≈ 0.641 g
4) To calculate the number of moles of Pb reacted, we need to divide the mass of Pb reacted by its molar mass.
Molar mass of Pb = 207.2 g/mol (approximate)
Number of moles of Pb reacted = Mass of Pb reacted / Molar mass of Pb
Number of moles of Pb reacted ≈ 4.136 g / 207.2 g/mol
Number of moles of Pb reacted ≈ 0.0199 mol
5) To calculate the number of moles of S reacted, we need to divide the mass of S reacted by its molar mass.
Molar mass of S = 32.1 g/mol (approximate)
Number of moles of S reacted = Mass of S reacted / Molar mass of S
Number of moles of S reacted ≈ 0.641 g / 32.1 g/mol
Number of moles of S reacted ≈ 0.020 mol
6) To find the simplest whole-number ratio of the number of moles of Pb to the number of moles of S in the compound formed, we need to divide both values by the smaller value.
Smallest value of moles = 0.0199 mol (from Pb)
Dividing both values by 0.0199 mol gives us a ratio of approximately 1:1.
7) Therefore, the empirical formula for the compound formed is PbS.
To solve this problem, we will use the conservation of mass principle. According to this principle, the mass of the reactants must be equal to the mass of the products.
1) Calculate the mass of Pb reacted.
Mass of Pb = Mass of crucible, cover, and Pb - Mass of crucible and cover
Mass of Pb = 32.025 g - 27.889 g
Mass of Pb = 4.136 g
2) Calculate the mass of the compound that formed.
Mass of compound = Mass of crucible, cover, and compound formed - Mass of crucible and cover
Mass of compound = 32.666 g - 27.889 g
Mass of compound = 4.777 g
3) Calculate the mass of S reacted.
Mass of S = Mass of compound formed - Mass of Pb
Mass of S = 4.777 g - 4.136 g
Mass of S = 0.641 g
4) Calculate the number of moles of Pb reacted.
Number of moles of Pb = Mass of Pb / Molar mass of Pb
The molar mass of Pb is obtained from the periodic table as 207.2 g/mol.
Number of moles of Pb = 4.136 g / 207.2 g/mol
Number of moles of Pb = 0.02 mol
5) Calculate the number of moles of S reacted.
Number of moles of S = Mass of S / Molar mass of S
The molar mass of S is obtained from the periodic table as 32.06 g/mol.
Number of moles of S = 0.641 g / 32.06 g/mol
Number of moles of S = 0.02 mol
6) Find the simplest whole-number ratio of the number of moles of Pb to the number of moles of S in the compound formed.
Since the moles of Pb and S are both 0.02 mol, the ratio is 1:1.
7) Write the empirical formula for the compound formed.
The empirical formula is the simplest whole-number ratio of atoms in a compound, so in this case, the empirical formula is PbS.
To answer these questions, we can use the principles of stoichiometry and the information provided in the data. Here's how you can approach each question:
1) Calculate the mass of Pb reacted:
- We can find the mass of Pb reacted by subtracting the mass of the crucible and cover from the mass of the crucible, cover, and Pb.
- Mass of Pb reacted = Mass of crucible, cover, and Pb - Mass of crucible and cover
2) Calculate the mass of compound that formed:
- We can find the mass of the compound formed by subtracting the mass of the crucible and cover from the mass of the crucible, cover, and compound formed.
- Mass of compound formed = Mass of crucible, cover, and compound formed - Mass of crucible and cover
3) Calculate the mass of S reacted:
- Since we know the total mass of the compound formed and the mass of Pb reacted, we can use the law of conservation of mass to determine the mass of S reacted.
- Mass of S reacted = Mass of compound formed - Mass of Pb reacted
4) Calculate the number of moles of Pb reacted:
- To calculate the number of moles, we need to use the molar mass of Pb, which is the atomic mass of Pb (207.2 g/mol).
- Number of moles of Pb reacted = Mass of Pb reacted / Molar mass of Pb
5) Calculate the number of moles of S reacted:
- To calculate the number of moles, we need to use the molar mass of S, which is the atomic mass of S (32.06 g/mol).
- Number of moles of S reacted = Mass of S reacted / Molar mass of S
6) Find the simplest whole-number ratio of the number of moles of Pb to the number of moles of S in the compound formed:
- Divide the number of moles of Pb and the number of moles of S by the smallest number of moles among them. Round to the nearest whole number.
7) Write the empirical formula for the compound formed:
- The empirical formula represents the simplest whole-number ratio of atoms in the compound.
- Use the ratio calculated in the previous step to write the empirical formula, where the subscript of each element represents the number of atoms in the compound.