Percentage of calcium in calcium carbonate is___________________?
Correct answer: C. 40%
- A. 80%
- B. 30%
- C. 40%
- D. 20%
Explanation
Using CaCO3 = 40 + 12 + (3 x 16) = 100 g mol^-1, the calcium percentage is (40 g mol^-1 / 100 g mol^-1) x 100 = 40%. The unit cancels in the ratio, leaving a percentage. Students may choose b by using 30 g mol^-1, which is close to the carbon dioxide portion rather than the calcium portion.
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About Moles and Avogadro's Number
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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