Galena is a major lead ore mineral and has the chemical formula PbS. What is the percentage of lead in galena?
Use the chemical formula to determine the percent composition.
Write the formula for galena: PbS
Determine the formula weight of galena:
Atoms Atomic Weight Total
1 of Pb 1×0
1 of S 1x
Formula weight = u
The Correct Answer and Explanation is :
To determine the percentage of lead in galena (PbS), we will need to calculate the formula weight of the mineral and then calculate the percent composition of lead in the formula.
1. Write the Formula for Galena:
The chemical formula for galena is PbS, which means it is made of one lead (Pb) atom and one sulfur (S) atom.
2. Determine the Atomic Weights:
The atomic weights of the elements involved are:
- Lead (Pb) has an atomic weight of approximately 207.2 u.
- Sulfur (S) has an atomic weight of approximately 32.07 u.
3. Calculate the Formula Weight:
The formula weight of galena is the sum of the atomic weights of all the atoms in the formula:
- For 1 atom of Pb: ( 1 \times 207.2 \, \text{u} = 207.2 \, \text{u} )
- For 1 atom of S: ( 1 \times 32.07 \, \text{u} = 32.07 \, \text{u} )
Therefore, the total formula weight of galena is:
[
\text{Formula Weight of PbS} = 207.2 + 32.07 = 239.27 \, \text{u}
]
4. Calculate the Percent Composition of Lead in Galena:
To find the percentage of lead (Pb) in galena, we use the following formula:
[
\text{Percent of Pb} = \left( \frac{\text{Atomic weight of Pb}}{\text{Formula weight of PbS}} \right) \times 100
]
Substituting the known values:
[
\text{Percent of Pb} = \left( \frac{207.2}{239.27} \right) \times 100 \approx 86.6\%
]
Conclusion:
The percentage of lead (Pb) in galena (PbS) is approximately 86.6%.
Explanation:
The process involves determining the atomic weights of the elements that make up the compound and using those weights to calculate the total formula weight of the mineral. The percentage of lead is determined by dividing the atomic weight of lead by the total formula weight and multiplying by 100. This process of calculating percent composition helps to understand how much of a specific element is present in a compound by weight.