1. **Stating the problem:** Convert grams (g) of a substance to the number of particles using moles and Avogadro's number. 2. **Formula and rules:** - First, convert grams to moles using the formula: $$\text{moles} = \frac{\text{mass in grams}}{\text{molar mass (g/mol)}}$$ - Then, convert moles to number of particles using Avogadro's number: $$\text{number of particles} = \text{moles} \times 6.022 \times 10^{23}$$ 3. **Step-by-step explanation:** - Given a mass in grams, divide by the molar mass to find moles. - Multiply the moles by Avogadro's number to find the number of particles. 4. **Example:** Suppose you have $10$ grams of water (H$_2$O) with molar mass $18$ g/mol. 5. Convert grams to moles: $$\text{moles} = \frac{10}{18} = \frac{\cancel{10}}{\cancel{18}} = 0.5555...$$ 6. Convert moles to particles: $$\text{number of particles} = 0.5555... \times 6.022 \times 10^{23} = 3.345 \times 10^{23}$$ **Final answer:** $$\boxed{3.345 \times 10^{23} \text{ particles}}$$