How many formula units are contained in 23.5g of Sb2S3
The Correct Answer and Explanation is:
To calculate the number of formula units in 23.5 g of ( \text{Sb}_2\text{S}_3 ) (antimony(III) sulfide), we need to follow a few key steps:
Step 1: Calculate the molar mass of ( \text{Sb}_2\text{S}_3 )
The molar mass of ( \text{Sb}_2\text{S}_3 ) can be found by adding the atomic masses of antimony (Sb) and sulfur (S), considering the subscripts in the formula. The atomic masses are approximately:
- Antimony (Sb): 121.76 g/mol
- Sulfur (S): 32.06 g/mol
So, the molar mass of ( \text{Sb}_2\text{S}_3 ) is:
[
\text{Molar mass of } \text{Sb}_2\text{S}_3 = (2 \times 121.76) + (3 \times 32.06) = 243.52 + 96.18 = 339.70 \, \text{g/mol}
]
Step 2: Calculate the number of moles in 23.5 g of ( \text{Sb}_2\text{S}_3 )
Next, we use the formula for moles:
[
\text{Moles of } \text{Sb}_2\text{S}_3 = \frac{\text{mass}}{\text{molar mass}} = \frac{23.5 \, \text{g}}{339.70 \, \text{g/mol}} = 0.0692 \, \text{mol}
]
Step 3: Calculate the number of formula units
The number of formula units in one mole of a substance is given by Avogadro’s number, which is approximately ( 6.022 \times 10^{23} ) formula units per mole. Therefore, the number of formula units in 0.0692 moles of ( \text{Sb}_2\text{S}_3 ) is:
[
\text{Number of formula units} = 0.0692 \, \text{mol} \times (6.022 \times 10^{23} \, \text{units/mol}) = 4.17 \times 10^{22} \, \text{formula units}
]
Final Answer:
The number of formula units in 23.5 g of ( \text{Sb}_2\text{S}_3 ) is approximately ( 4.17 \times 10^{22} ) formula units.
Explanation:
This calculation involves converting the mass of a compound into moles using its molar mass, and then using Avogadro’s number to convert moles into formula units. These steps are foundational in chemistry for understanding the relationship between mass, moles, and the number of individual particles in a sample.