A sample of an iron and oxygen ore has a mass of 35.8 grams. The iron in the compound has a mass of 27.9 grams. What is the percent iron in the ore?
Correct answer: D. 78% Fe
- A. 74% Fe
- B. 75% Fe
- C. 77% Fe
- D. 78% Fe
Explanation
Percentage of iron = (mass of iron ÷ mass of ore) x 100 = (27.9 g ÷ 35.8 g) x 100 = 77.93%, which rounds to 78% Fe. Thus option d is correct. The closest alternative is c, 77% Fe, usually chosen when the decimal result is truncated instead of rounded.
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The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.
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