Caffeine has a molecular mass of 194. If it contains 28.9% by mass of nitrogen, 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 correct answer is 4, as the molecular formula for caffeine is C8H10N4O2. This means there are 4 nitrogen atoms in each molecule. The percentage composition of nitrogen (28.9%) corresponds to this number based on the molecular mass of 194. Other options such as 6, 2, or 3 nitrogen atoms would either increase or decrease the nitrogen percentage, not aligning with the given data.
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About Fundamental Concepts of Chemistry
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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