Question

A lawn fertilizer is rated as 7.35% nitrogen, meaning 7.35 g of N in 100 g of fertilizer. The nitrogen is present in the form of urea, (NH2)2CO. How many grams of urea are present in 100 g of the fertilizer to supply the rated amount of nitrogen?

Answer 1

Answer on Question#39864-Chemistry-Inorganic Chemistry

Question

A lawn fertilizer is rated as 7.35% nitrogen, meaning 7.35 g of N in 100 g of fertilizer. The nitrogen is present in the form of urea, $(\mathrm{NH}_2)_2\mathrm{CO}$. How many grams of urea are present in 100 g of the fertilizer to supply the rated amount of nitrogen?

Solution

Molar mass of urea $M_{\text{urea}} = 60 \, \text{g/mol}$.

Mass of nitrogen in 1 mol of urea $M_N^{\text{urea}} = 2 \cdot 14 = 28 \, \text{g/mol}$.

Thus, we may write the proportion

$60 \, \text{g/mol} \, (\text{urea}) - 28 \, \text{g/mol} \, (\text{N})$

X g (urea) - 7.35 g (N)

Hence $X = 60 \cdot 7.35 / 28 = 15.75 \, \text{g}$

Answer: 15.75 g