Worksheet: Mole Problems - Free Printable

Let's solve each part of the worksheet step by step.

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Part 1: Molar Mass

We need to calculate the molar mass of each compound using atomic masses from the periodic table. Here are approximate values (rounded to two decimal places):

- H = 1.01 g/mol
- Cl = 35.45 g/mol
- K = 39.10 g/mol
- C = 12.01 g/mol
- O = 16.00 g/mol
- Ca = 40.08 g/mol
- Na = 22.99 g/mol
- P = 30.97 g/mol

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#### 1. HCl
- H: 1.01 g/mol
- Cl: 35.45 g/mol
Molar mass = 1.01 + 35.45 = 36.46 g/mol

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#### 2. K₂CO₃
- K: 2 × 39.10 = 78.20 g/mol
- C: 12.01 g/mol
- O: 3 × 16.00 = 48.00 g/mol
Molar mass = 78.20 + 12.01 + 48.00 = 138.21 g/mol

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#### 3. Ca(OH)₂
- Ca: 40.08 g/mol
- O: 2 × 16.00 = 32.00 g/mol
- H: 2 × 1.01 = 2.02 g/mol
Molar mass = 40.08 + 32.00 + 2.02 = 74.10 g/mol

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#### 4. Na₃PO₄
- Na: 3 × 22.99 = 68.97 g/mol
- P: 30.97 g/mol
- O: 4 × 16.00 = 64.00 g/mol
Molar mass = 68.97 + 30.97 + 64.00 = 163.94 g/mol

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✔ Part 1 Answers:

- HCl: 36.46 g/mol
- K₂CO₃: 138.21 g/mol
- Ca(OH)₂: 74.10 g/mol
- Na₃PO₄: 163.94 g/mol

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Part 2: Mole Conversions

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#### 1. How many atoms are in 6.2 moles of aluminum?

We use Avogadro's number:
1 mole = 6.022 × 10²³ atoms

So:
$$
6.2 \text{ mol} \times 6.022 \times 10^{23} \text{ atoms/mol} = 3.73364 \times 10^{24} \text{ atoms}
$$

Answer: $ \boxed{3.73 \times 10^{24}} $ atoms (rounded to 3 significant figures)

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#### 2. Convert 5.3 × 10²⁵ molecules of CO₂ to moles

Use:
$$
\text{moles} = \frac{\text{number of molecules}}{6.022 \times 10^{23}}
$$

$$
\frac{5.3 \times 10^{25}}{6.022 \times 10^{23}} = 87.99 \approx 88.0 \text{ moles}
$$

Answer: $ \boxed{88.0} $ moles (3 significant figures)

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#### 3. How many formula units of sodium acetate are in 0.87 moles of sodium acetate?

Sodium acetate is an ionic compound, so we use formula units.

$$
0.87 \text{ mol} \times 6.022 \times 10^{23} \text{ formula units/mol} = 5.23714 \times 10^{23}
$$

Answer: $ \boxed{5.24 \times 10^{23}} $ formula units (3 significant figures)

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#### 4. Convert 3.55 moles NaCl to formula units

$$
3.55 \text{ mol} \times 6.022 \times 10^{23} = 2.14311 \times 10^{24}
$$

Answer: $ \boxed{2.14 \times 10^{24}} $ formula units (3 significant figures)

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✔ Final Answers:

#### Part 1: Molar Mass
- HCl: 36.46 g/mol
- K₂CO₃: 138.21 g/mol
- Ca(OH)₂: 74.10 g/mol
- Na₃PO₄: 163.94 g/mol

#### Part 2: Mole Conversions
1. 3.73 × 10²⁴ atoms
2. 88.0 moles
3. 5.24 × 10²³ formula units
4. 2.14 × 10²⁴ formula units

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