Urea as a fertilizer contains:____________?
Correct answer: C. 46% N
- A. 57% N
- B. 73% N
- C. 46% N
- D. 53% N
Explanation
Urea is CO(NH2)2, with molar mass 12 + 16 + 2(14) + 4(1) = 60 g mol^-1. Nitrogen contributes 28 g mol^-1, so percentage nitrogen = (28 g mol^-1 / 60 g mol^-1) x 100 = 46.7%, reported commercially as 46% N. Students often choose 57% by using an incorrect molar mass or nitrogen percentage.
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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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