Question

Urea, chemical formula `(NH_2)_2CO`, is used for fertilizer and many other things. How do you calculate the number of N,C, O, and H atoms in `1.68 x 10^4` g of urea?

Answer 1

You have 1680 grams of urea. It means (in it) there are 787 grams of nitrogen, 112 grams of hydrogen, 336 grams of carbon, and 448 grams of oxygen.

Explanation:

Masses:
Nitrogen = 14 grams
Hydrogen= 1 gram
Carbon = 12 grams
Oxygen= 16 grams

In one mole of urea, we have 28 grams of nitrogen, 4 grams of hydrogen, 12 grams of carbon, and 16 grams of oxygen. In other words, one mole of urea has a molecular weight of 60 grams.

The question is: "If you have 1680 grams of urea, what is the mole number in it?"

The solution of this question: `1680/60 = 28` moles.

Now, what is the elemental weights in 28 moles of urea:

For nitrogen `=28times28=784` grams
For hydrogen `=4times28=112` grams
For carbon `=12times28=336` grams
For oxygen `=16times28=448` grams

The sum of these (`784+112+336+448`) is approximately 1680 grams.