The number of N atoms in 681 g of C₇H₅N₃O₆ is x × 10²¹. The value of x is (N A = 6.02 × 10²³ mol⁻¹) (Nearest Integer)

Solution

Chemistry ma’am · 4 steps

Find moles of the compound first, then multiply by 3, because every molecule carries three N atoms.

1. Molar mass. For C₇H₅N₃O₆: 7 × 12 + 5 × 1 + 3 × 14 + 6 × 16 = 84 + 5 + 42 + 96 = 227 g mol⁻¹.
2. Moles of compound. 681/227 = 3 mol of C₇H₅N₃O₆. Each molecule has 3 N atoms, so there are 3 × 3 = 9 mol of N atoms.

   N_(N atoms) = 9 × 6.02 × 10²³ = 5.418 × 10²⁴

3. Match the form. To write it as x × 10²¹, move the decimal three places: 5.418 × 10²⁴ = 5418 × 10²¹.
4. So. x = 5418.

The common slip: 1806. Forgetting the 3 N atoms per molecule counts molecules, not atoms, and gives 1806.

The idea to keep. Atoms of one element = moles of compound × number of that atom in the formula × N_A. Then rewrite the power of ten to match the form the question asks for.

Answer from the NTA final answer key. Solution by PrepWiser.