Question

35g of water. how many moles
11g of H3PO4
500g Mg(NO3)2
1kg NaF
1.2 kg Ca(OH)2

Answer 1

To calculate the number of moles for each substance, you can use the formula:

\[
\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}
\]

Let's calculate the moles for each substance one by one:

1. **Water (H₂O)**:
- Molar mass of H₂O: \(2 \times 1.01 \, (H) + 16.00 \, (O) = 18.02 \, g/mol\)
- Moles of water:
\[
\frac{35 \, g}{18.02 \, g/mol} \approx 1.94 \, \text{moles}
\]

2. **H₃PO₄ (Phosphoric Acid)**:
- Molar mass of H₃PO₄: \(3 \times 1.01 \, (H) + 30.97 \, (P) + 4 \times 16.00 \, (O) = 98.00 \, g/mol\)
- Moles of H₃PO₄:
\[
\frac{11 \, g}{98.00 \, g/mol} \approx 0.112 \, \text{moles}
\]

3. **Mg(NO₃)₂ (Magnesium Nitrate)**:
- Molar mass of Mg(NO₃)₂: \(24.31 \, (Mg) + 2 \times (14.01 \, (N) + 3 \times 16.00 \, (O))\)
- Calculating:
\[
= 24.31 + 2 \times (14.01 + 48.00) = 24.31 + 2 \times 62.01 = 24.31 + 124.02 = 148.33 \, g/mol
\]
- Moles of Mg(NO₃)₂:
\[
\frac{500 \, g}{148.33 \, g/mol} \approx 3.37 \, \text{moles}
\]

4. **NaF (Sodium Fluoride)**:
- Molar mass of NaF: \(22.99 \, (Na) + 19.00 \, (F) = 41.99 \, g/mol\)
- Convert 1 kg to grams: \(1 \, kg = 1000 \, g\)
- Moles of NaF:
\[
\frac{1000 \, g}{41.99 \, g/mol} \approx 23.82 \, \text{moles}
\]

5. **Ca(OH)₂ (Calcium Hydroxide)**:
- Molar mass of Ca(OH)₂: \(40.08 \, (Ca) + 2 \times (1.01 \, (O) + 16.00 \, (H))\)
- Calculating:
\[
= 40.08 + 2 \times (1.01 + 16.00) = 40.08 + 2 \times 17.01 = 40.08 + 34.02 = 74.10 \, g/mol
\]
- Convert 1.2 kg to grams: \(1.2 \, kg = 1200 \, g\)
- Moles of Ca(OH)₂:
\[
\frac{1200 \, g}{74.10 \, g/mol} \approx 16.19 \, \text{moles}
\]

### Summary of Moles:
- Water: **1.94 moles**
- H₃PO₄: **0.112 moles**
- Mg(NO₃)₂: **3.37 moles**
- NaF: **23.82 moles**
- Ca(OH)₂: **16.19 moles**