How many formula units are contained in 23.5g of Sb2S3
The correct answer and explanation is:
Let’s solve the problem step-by-step.
Question:
How many formula units are contained in 23.5 g of Sb₂S₃ (antimony(III) sulfide)?
Step 1: Find the molar mass of Sb₂S₃
- Atomic mass of Sb (Antimony) ≈ 121.76 g/mol
- Atomic mass of S (Sulfur) ≈ 32.06 g/mol
Molar mass of Sb₂S₃ = (2 × 121.76) + (3 × 32.06)
= 243.52 + 96.18
= 339.70 g/mol
Step 2: Calculate the number of moles in 23.5 g of Sb₂S₃
Number of moles = mass / molar mass
= 23.5 g / 339.70 g/mol
≈ 0.0692 moles
Step 3: Calculate the number of formula units
1 mole of any substance contains 6.022 × 10²³ formula units (Avogadro’s number).
Number of formula units = moles × Avogadro’s number
= 0.0692 × 6.022 × 10²³
≈ 4.17 × 10²² formula units
Final answer:
23.5 g of Sb₂S₃ contains approximately 4.17 × 10²² formula units.
Explanation (300 words):
When dealing with compounds like Sb₂S₃, we often want to know how many discrete units of the compound are present in a certain mass. These discrete units are called formula units for ionic or covalent network compounds, analogous to molecules in molecular substances.
The first step is to determine the molar mass of Sb₂S₃. This is the mass of one mole of the compound and is found by adding the atomic masses of all the atoms in one formula unit. Antimony (Sb) has an atomic mass of about 121.76 g/mol, and sulfur (S) has an atomic mass of 32.06 g/mol. Since Sb₂S₃ contains 2 atoms of Sb and 3 atoms of S, we multiply accordingly and sum these masses, which results in approximately 339.70 g/mol.
Next, you find how many moles are in the 23.5 g sample by dividing the sample’s mass by the molar mass. This gives approximately 0.0692 moles. A mole represents a quantity of particles equal to Avogadro’s number (6.022 × 10²³).
Finally, to get the total number of formula units, multiply the number of moles by Avogadro’s number. This conversion allows us to go from macroscopic quantities of a compound to the microscopic number of particles. The result is about 4.17 × 10²² formula units.
This calculation is useful in chemistry because many reactions and properties depend on the number of formula units or molecules, not just the mass, allowing chemists to understand and predict how substances will behave at the microscopic level.