Worksheet for practicing molar mass calculations in chemistry.

Here are the step-by-step solutions for the problems on your worksheet.

1. How many molecules are in 15.0 g of sulfur dioxide, SO₂?

* Step 1: Find the molar mass of SO₂.
* Sulfur (S) has a mass of about 32.07 g/mol.
* Oxygen (O) has a mass of about 16.00 g/mol.
* Molar Mass = $32.07 + (2 \times 16.00) = 64.07$ g/mol.
* Step 2: Convert grams to moles.
* $\text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}}$
* $\text{Moles} = \frac{15.0}{64.07} \approx 0.2341$ mol.
* Step 3: Convert moles to molecules.
* Multiply by Avogadro's number ($6.022 \times 10^{23}$).
* $0.2341 \times (6.022 \times 10^{23}) \approx 1.41 \times 10^{23}$.

2. What is the mass of 2.29 x 10²⁴ atoms of sulfur?

* Step 1: Convert atoms to moles.
* Divide the number of atoms by Avogadro's number ($6.022 \times 10^{23}$).
* $\text{Moles} = \frac{2.29 \times 10^{24}}{6.022 \times 10^{23}} \approx 3.803$ mol.
* Step 2: Convert moles to mass.
* The atomic mass of Sulfur (S) is 32.07 g/mol.
* $\text{Mass} = \text{Moles} \times \text{Molar Mass}$
* $\text{Mass} = 3.803 \times 32.07 \approx 121.96$ g.
* Rounding to 3 significant figures gives 122 g.

3. How many formula units of silver fluoride, AgF, are equal to 42.15 g of this substance?

* Step 1: Find the molar mass of AgF.
* Silver (Ag) is 107.87 g/mol.
* Fluorine (F) is 19.00 g/mol.
* Molar Mass = $107.87 + 19.00 = 126.87$ g/mol.
* Step 2: Convert grams to moles.
* $\text{Moles} = \frac{42.15}{126.87} \approx 0.3322$ mol.
* Step 3: Convert moles to formula units.
* Multiply by Avogadro's number.
* $0.3322 \times (6.022 \times 10^{23}) \approx 2.00 \times 10^{23}$.

4. What is the mass of 8.83 x 10²³ formula units of iron (III) oxide, Fe₂O₃?

* Step 1: Find the molar mass of Fe₂O₃.
* Iron (Fe) is 55.85 g/mol.
* Oxygen (O) is 16.00 g/mol.
* Molar Mass = $(2 \times 55.85) + (3 \times 16.00) = 111.7 + 48.00 = 159.7$ g/mol.
* Step 2: Convert formula units to moles.
* $\text{Moles} = \frac{8.83 \times 10^{23}}{6.022 \times 10^{23}} \approx 1.466$ mol.
* Step 3: Convert moles to mass.
* $\text{Mass} = 1.466 \times 159.7 \approx 234.1$ g.
* Rounding to 3 significant figures gives 234 g.

Final Answer:
1. 1.41 x 10²³ molecules
2. 122 g
3. 2.00 x 10²³ formula units
4. 234 g