What is the mass of potassium chloride produced when $12.25\ \mathrm{g}$ potassium chlorate undergoes decomposition? (Atomic masses: $\mathrm{K} = 39$, $\mathrm{Cl} = 35.5$, $\mathrm{O} = 16$)
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Notice how clean the numbers are! The given mass ($12.25\ \mathrm{g}$) is exactly one-tenth of the molar mass of $\mathrm{KClO}_3$ ($122.5\ \mathrm{g}$). Since the molar ratio is $1:1$, the answer must simply be one-tenth of the molar mass of $\mathrm{KCl}$ ($74.5\ \mathrm{g}$), which gives $7.45\ \mathrm{g}$ with zero heavy calculations.
Step 1: Understanding the Question: Find mass of KCl produced from complete thermal decomposition of 12.25 g KClO₃. Step 2: Detailed Explanation: Balanced equation: 2KClO₃ → 2KCl + 3O₂ (1:1 mole ratio). Molar mass KClO₃ = 39 + 35.5 + 48 = 122.5 g/mol. Moles KClO₃ = 12.25/122.5 = 0.1 mol. So moles KCl = 0.1 mol. Molar mass KCl = 74.5 g/mol. Mass KCl = 0.1 × 74.5 = 7.45 g. Step 3: Final Answer: Mass of KCl produced is 7.45 g, option (C).