Caffeine has a molecular mass of 194. If it contains 28.9% by mass of nitrogen, the number of atoms of nitrogen in one molecule of caffeine is:
Correct answer: A. 4
- A. 4
- B. 6
- C. 2
- D. 3
Explanation
The total mass of nitrogen in one mole of caffeine is 0.289 × 194 ≈ 56.06 g. Dividing this by the atomic mass of nitrogen (14 g/mol) gives approximately 4 moles. Thus, there are 4 nitrogen atoms per molecule.
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Mole calculations connect mass, number of particles and Avogadro's number, while balanced equations provide the mole ratios used in stoichiometry. Questions cover limiting and excess reactants, theoretical yield and percentage yield, including identifying which reactant is consumed first and comparing the actual product with the maximum possible product.
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