Molar Mass Conversion Worksheet for chemistry students to practice calculating molar masses and converting between grams and moles.

Let’s solve each part step by step.

---

Part I: Molar Mass Calculations

We’ll use the periodic table to find atomic masses (rounded to hundredths):

- H = 1.01 g/mol
- O = 16.00 g/mol
- Mg = 24.31 g/mol
- Cl = 35.45 g/mol
- C = 12.01 g/mol
- N = 14.01 g/mol
- Ag = 107.87 g/mol
- Pb = 207.20 g/mol
- I = 126.90 g/mol
- Al = 26.98 g/mol

Now calculate each:

1. H₂ → 2 × 1.01 = 2.02 g/mol

2. O₂ → 2 × 16.00 = 32.00 g/mol

3. H₂O → (2 × 1.01) + 16.00 = 2.02 + 16.00 = 18.02 g/mol

4. H₂O₂ → (2 × 1.01) + (2 × 16.00) = 2.02 + 32.00 = 34.02 g/mol

5. MgCl₂ → 24.31 + (2 × 35.45) = 24.31 + 70.90 = 95.21 g/mol

6. CH₄ → 12.01 + (4 × 1.01) = 12.01 + 4.04 = 16.05 g/mol

7. (NH₄)₂O → First, NH₄ is one nitrogen + four hydrogens = 14.01 + 4.04 = 18.05
Two of those: 2 × 18.05 = 36.10
Plus oxygen: 36.10 + 16.00 = 52.10 g/mol

8. AgNO₃ → Ag = 107.87, N = 14.01, O₃ = 3×16.00=48.00
Total: 107.87 + 14.01 + 48.00 = 169.88 g/mol

9. PbI₂ → Pb = 207.20, I₂ = 2×126.90 = 253.80
Total: 207.20 + 253.80 = 461.00 g/mol

10. Al(CN)₃ → Al = 26.98
CN group: C + N = 12.01 + 14.01 = 26.02
Three groups: 3 × 26.02 = 78.06
Total: 26.98 + 78.06 = 105.04 g/mol

✔ Part I Answers:
1. 2.02
2. 32.00
3. 18.02
4. 34.02
5. 95.21
6. 16.05
7. 52.10
8. 169.88
9. 461.00
10. 105.04

---

Part II: Dimensional Analysis

Use molar mass as conversion factor between grams and moles.

Formula:
→ Moles = grams ÷ molar mass
→ Grams = moles × molar mass

1. How many moles in 9.06g of H₂?
Molar mass H₂ = 2.02 g/mol
Moles = 9.06 ÷ 2.02 ≈ ?

Let’s calculate:
9.06 ÷ 2.02 = 4.485... → round to nearest hundredth? The problem doesn’t specify for this part, but since inputs are given to 3 sig figs, we can keep 3 sig figs.

Actually, let’s do exact division:
9.06 / 2.02 = 4.485148... → 4.49 mol (if rounding to 3 sig figs)

But wait — 9.06 has 3 sig figs, 2.02 has 3 → answer should have 3 → 4.49 mol

✔ Answer: 4.49 mol

2. Grams in 0.82 moles of O₂?
Molar mass O₂ = 32.00 g/mol
Grams = 0.82 × 32.00 = ?

0.82 × 32 = 26.24 → 26.24 g

Sig figs: 0.82 has 2 sig figs → so answer should be 26 g? Wait — but 32.00 is exact? No, it’s measured. So 0.82 has 2 sig figs → answer should have 2 → 26 g

BUT — looking at worksheet instructions: “round each molar mass to nearest hundredth” — but for calculations, they don’t specify. Since 0.82 has two decimal places but only 2 sig figs, and 32.00 has 4, we go with least precise → 2 sig figs.

However, in many school settings, if the number like 0.82 is given, they expect you to multiply directly and report as is unless told otherwise.

Let’s check: 0.82 × 32.00 = 26.24 → probably acceptable as 26.24 g, but to match sig figs → 26 g

Hmm — let me see the other problems. Problem 3 uses 2.78 (3 sig figs), problem 4 uses 0.49 (2 sig figs). Probably they want full calculation without strict sig fig enforcement here.

Looking back at Part I instruction: “round each molar mass to nearest hundredth” — but for Part II, no such instruction. So I’ll compute exactly and report as calculated.

So: 0.82 × 32.00 = 26.24 g

✔ Answer: 26.24 g

3. Grams in 2.78 mol of H₂O?
Molar mass H₂O = 18.02 g/mol
Grams = 2.78 × 18.02 = ?

Calculate:
2.78 × 18 = 50.04
2.78 × 0.02 = 0.0556
Total = 50.04 + 0.0556 = 50.0956 → 50.10 g (rounded to hundredth)

Or directly: 2.78 × 18.02 = let's do it properly:

2.78 × 18.02
= 2.78 × (18 + 0.02) = 2.78×18 = 50.04; 2.78×0.02=0.0556 → total 50.0956 → rounds to 50.10 g

✔ Answer: 50.10 g

4. Grams in 0.49 mol of H₂O₂?
Molar mass H₂O₂ = 34.02 g/mol
Grams = 0.49 × 34.02 = ?

0.49 × 34 = 16.66
0.49 × 0.02 = 0.0098
Total = 16.6698 → 16.67 g (rounded to hundredth)

Direct multiplication: 0.49 × 34.02 = 16.6698 → 16.67 g

✔ Answer: 16.67 g

---

Final Answer:

Part I:
1. 2.02
2. 32.00
3. 18.02
4. 34.02
5. 95.21
6. 16.05
7. 52.10
8. 169.88
9. 461.00
10. 105.04

Part II:
1. 4.49 mol
2. 26.24 g
3. 50.10 g
4. 16.67 g