The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is    [Cu = 63.5, O = 16]

Analyze the question: You are given the moles of each element directly (0.067 mol Cu and 0.066 mol O). The empirical formula is the simplest whole-number ratio of atoms, so we only need the mole ratio.

Concept: Empirical formula steps:

1. Find moles of each element (already given here).
2. Divide by the smallest number of moles.
3. Round to the nearest whole numbers to get the ratio.

The atomic masses (Cu = 63.5, O = 16) are not needed, because the moles are already given. They would only be used if masses or percentages were provided.

Solution:

| Element | Moles | Divide by smallest (0.066) | Ratio | |---|---|---|---| | Cu | 0.067 | 0.067 ÷ 0.066 ≈ 1.01 | 1 | | O | 0.066 | 0.066 ÷ 0.066 = 1 | 1 |

The ratio Cu : O = 1 : 1, so the empirical formula is CuO.

Answer: Option B, CuO.

Tip: Always check whether the question gives moles, masses or percentages. If it gives moles, skip straight to the division step. Do not waste time converting with atomic masses. Also, if the ratio comes out very close to a whole number (like 1.01), just round it. Only multiply to clear fractions when you get something like 1.5 or 1.33.