Calculate the number of nitrogen atoms in 20 g of urea (carbamide) containing 10% non-nitrogenous impurities.

Urea is a chemical compound, the composition of which is described by the gross formula – CH4N2O.
First of all, we calculate the mass of urea without impurities, since the percentage of impurities is known (10%).
m (CH4N2O) = 20 * 0.9 = 18 g
Let’s calculate the molecular weight of urea and the number of moles.
M (CH4N2O) = 12 + 4 + 14 * 2 + 16 = 60 g / mol
n (CH4N2O) = m / M = 18/60 = 0.3 mol
To calculate the number of nitrogen atoms, you need to know the number of moles of nitrogen in urea.
n (N) = 0.3 * 2 = 0.6 mol (since there are two nitrogen atoms)
Let’s multiply n by Avogadro’s number and calculate the number of nitrogen atoms.
N = n * Na = 0.6 * 6.02 * 10 ^ 23 = 3.6 * 10 ^ 23