1. **Problem statement:** a) Calculate the relative formula mass of methane (CH$_4$). b) Calculate the percentage by mass of carbon in methane. 2. **Given data:** Relative atomic masses (A$_r$): C = 12, H = 1 3. **Formula for relative formula mass (Mr):** $$\text{Mr} = \sum (\text{number of atoms} \times \text{relative atomic mass})$$ 4. **Calculate Mr of methane (CH$_4$):** Carbon atoms: 1 \times 12 = 12 Hydrogen atoms: 4 \times 1 = 4 Total Mr = 12 + 4 = 16 5. **Calculate percentage by mass of carbon:** $$\% \text{C} = \frac{\text{mass of C}}{\text{Mr of CH}_4} \times 100 = \frac{12}{16} \times 100 = 75\%$$ --- 6. **Next problem:** Calculate the range and uncertainty of the mass dissolved data. 7. **Data:** 5.8, 5.2, 6.1, 5.3 g 8. **Calculate range:** $$\text{Range} = \text{max} - \text{min} = 6.1 - 5.2 = 0.9\,g$$ 9. **Calculate uncertainty:** Uncertainty is half the range: $$\text{Uncertainty} = \frac{0.9}{2} = 0.45\,g$$ 10. **Final result with uncertainty:** $$5.6 \pm 0.45\,g$$