Formula for calculating the mass fraction of an element in a substance:
w = n * Ar (chemical element) / Mr (substance), where n is the number of atoms of a given chemical element.
1) Find the relative molecular weight of the substance (NH3):
Mr (NH3) = Ar (N) + 3 * Ar (H) = 14 + 3 = 17;
2) Find the mass fraction of a given element in the substance:
w (N) = 14/17 = 0.82 or 82%;
1 way: w (H) = 3/17 = 0.18 or 18% or 2 way: w (H) = 100 – 82 = 18%.
Answer: Mass fraction of nitrogen in ammonia is 82%. Mass fraction of hydrogen in ammonia is 18%.
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