Final answer:
To find the empirical formula of a compound from combustion analysis, calculate the moles of carbon from CO₂ and hydrogen from H₂O, then find moles of oxygen in the original compound. Divide moles of each by the smallest number to get the mole ratio. The final empirical formula is derived from these ratios.
Step-by-step explanation:
To determine the empirical formula of a compound from combustion analysis, we need to find the moles of C, H, and O in the compound. We use the masses of CO₂ and H₂O produced to calculate this.
First, we calculate the moles of C by using the mass of CO₂ produced:
- 145.0 mg CO₂ * (1 mol CO₂ / 44.01 g CO₂) = 0.00329 mol C
Next, we find the moles of H by using the mass of H₂O produced:
- 59.38 mg H₂O * (1 mol H₂O / 18.02 g H₂O) * (2 mol H / 1 mol H₂O) = 0.00658 mol H
To find the moles of O in the original compound, we subtract the O atoms in CO₂ and H₂O from the total mass:
- Total mass of compound = 63.8 mg
- Mass of C (from CO₂) = 0.00329 mol * 12.01 g/mol = 0.0395 g
- Mass of H (from H₂O) = 0.00658 mol * 1.008 g/mol = 0.00663 g
- Mass of O in compound = total mass - mass of C - mass of H = 63.8 mg - 39.5 mg - 6.63 mg = 17.67 mg
- Moles of O = 17.67 mg * (1 mol O / 16.00 g O) = 0.00110 mol O
We then get the mole ratio of C : H : O by dividing by the smallest number of moles, which gives us the empirical formula. In this example, we calculate the ratio but the student will perform these calculations to get the empirical formula.