Question

Urea, chemical formula (NH2)2CO, is used for fertilizer and many other things. Calculate the number of N, C, O, and H atoms in 1.78 × 104 g of urea. Enter your answers in scientific notation.

Answer 1

Molar mass of (NH4)2CO,

MM = 2*MM(N) + 8*MM(H) + 1*MM(C) + 1*MM(O)

= 2*14.01 + 8*1.008 + 1*12.01 + 1*16.0

= 64.094 g/mol

mass((NH4)2CO)= 1780 g

use:

number of mol of (NH4)2CO,

n = mass of (NH4)2CO/molar mass of (NH4)2CO

=(1780.0 g)/(64.09 g/mol)

= 27.77 mol

use:

number of molecules = number of mol * Avogadro’s number

number of molecules = 27.77 * 6.022*10^23 molecules

number of molecules = 1.672*10^25 molecules

Count of each element in compound is:

{N=2, H=8, C=1, O=1}

1)

number of N = 2*number of molecules

= 2*1.672*10^25

= 3.34*10^25

2)

number of C = 1*number of molecules

= 1.672*10^25

3)

number of O = 1*number of molecules

= 1.672*10^25

4)

number of H = 8*number of molecules

= 8*1.672*10^25

= 1.34*10^26