Solved Moles, Molecules, and Grams Worksheet 1) How many | Chegg.com - Free Printable

Let’s solve each problem step by step. We’ll use the mole concept and Avogadro’s number (6.022 × 10²³) to convert between grams, moles, molecules, and atoms.

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Problem 1: How many molecules are there in 24 grams of FeF₃?

Step 1: Find the molar mass of FeF₃.
- Iron (Fe) = 55.85 g/mol
- Fluorine (F) = 19.00 g/mol → 3 F atoms = 3 × 19.00 = 57.00 g/mol
- Molar mass of FeF₃ = 55.85 + 57.00 = 112.85 g/mol

Step 2: Convert grams to moles.
→ Moles = mass / molar mass = 24 g / 112.85 g/mol ≈ 0.2127 mol

Step 3: Convert moles to molecules.
→ Molecules = moles × Avogadro’s number
= 0.2127 × 6.022 × 10²³ ≈ 1.281 × 10²³ molecules

✔ Final Answer for #1: 1.28 × 10²³ molecules (rounded to 3 significant figures)

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Problem 2: How many molecules are there in 450 grams of Na₂SO₄?

Step 1: Find the molar mass of Na₂SO₄.
- Sodium (Na) = 22.99 g/mol → 2 Na = 45.98 g/mol
- Sulfur (S) = 32.07 g/mol
- Oxygen (O) = 16.00 g/mol → 4 O = 64.00 g/mol
- Total = 45.98 + 32.07 + 64.00 = 142.05 g/mol

Step 2: Convert grams to moles.
→ Moles = 450 g / 142.05 g/mol ≈ 3.168 mol

Step 3: Convert moles to molecules.
→ Molecules = 3.168 × 6.022 × 10²³ ≈ 1.908 × 10²⁴ molecules

✔ Final Answer for #2: 1.91 × 10²⁴ molecules (rounded to 3 significant figures)

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Problem 3: How many grams are there in 2.3 × 10²⁴ atoms of silver?

Silver is an element, so we’re dealing with atoms → moles → grams.

Step 1: Convert atoms to moles.
→ Moles = atoms / Avogadro’s number
= (2.3 × 10²⁴) / (6.022 × 10²³) ≈ 3.819 mol

Step 2: Convert moles to grams.
Molar mass of Ag (silver) = 107.87 g/mol

→ Grams = moles × molar mass = 3.819 × 107.87 ≈ 412.0 g

✔ Final Answer for #3: 410 grams (rounded to 2 significant figures — because 2.3 has 2 sig figs)

Wait — let’s check: 2.3 × 10²⁴ has 2 significant figures, so answer should have 2.

3.819 mol × 107.87 g/mol = 412.0 → rounded to 2 sig figs = 410 g

But note: 410 has 2 sig figs if written as 4.1 × 10². Let’s write it properly.

Actually, 412.0 rounded to 2 sig figs is 410, but that can be ambiguous. Better to write as 4.1 × 10² g.

However, since the question says “how many grams”, and doesn’t specify format, we’ll go with 410 g (understood as 2 sig figs).

✔ Final Answer for #3: 410 grams

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Problem 4: How many grams are there in 7.4 × 10²³ molecules of AgNO₃?

Step 1: Convert molecules to moles.
→ Moles = molecules / Avogadro’s number
= (7.4 × 10²³) / (6.022 × 10²³) ≈ 1.229 mol

Step 2: Find molar mass of AgNO₃.
- Silver (Ag) = 107.87 g/mol
- Nitrogen (N) = 14.01 g/mol
- Oxygen (O) = 16.00 g/mol → 3 O = 48.00 g/mol
- Total = 107.87 + 14.01 + 48.00 = 169.88 g/mol

Step 3: Convert moles to grams.
→ Grams = 1.229 mol × 169.88 g/mol ≈ 208.8 g

Check significant figures: 7.4 × 10²³ has 2 sig figs → answer should have 2.

208.8 → rounded to 2 sig figs = 210 g

✔ Final Answer for #4: 210 grams

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Final Answer:
1) 1.28 × 10²³ molecules
2) 1.91 × 10²⁴ molecules
3) 410 grams
4) 210 grams