You must first calculate the total weight of 1 mole of the substance. You do this by finding the molar weights on the periodic table of each of the elements in the compound:
[tex] 8(12.01g)+10(1.008g)+4(14.007g)+2(15.999g)=96.08g+10.08g+56.028g+31.998g=194.186g [/tex]
So now we take the amount of each element that is given in the compound and divide it by the total mass of the compound:
Carbon: 96.08g
[tex] \frac{96.08g}{194.186g}= 0.49478=49.48 [/tex]
Carbon = 49.48%
Nitrogen: 56.028g
[tex] \frac{56.028g}{194.186g}=0.28853=28.85 [/tex]
Nitrogen = 28.85%
Oxygen: 31.998g
[tex] \frac{31.998g}{194.186g} =0.16478=16.48 [/tex]
Oxygen = 16.48%
Explanation:
Molecular mass of carbon caffeine([tex]C_8H_{10}N_4O_2[/tex]), = 194 g/mol
Atomic mass of carbon = 12 g/mol
Atomic mass of hydrogen atom = 1 g/mol
Atomic mass of nitrogen atom = 1 g/mol
Atomic mass of oxygen atom = 1 g/mol
Percentage of an element in a compound:
[tex]\frac{\text{Number of atoms of element}\times \text{Atomic mass of element}}{\text{molecular mass of compound}}\times 100[/tex]
Percentage of carbon:
[tex]\frac{8\times 12 g/mol}{194 g/mol}\times 100=49.48\%[/tex]
Percentage of hydrogen:
[tex]\frac{10\times 1g/mol}{194 g/mol}\times 100=5.15\%[/tex]
Percentage of nitrogen:
[tex]\frac{4\times 14 g/mol}{194 g/mol}\times 100=28.86\%[/tex]
Percentage of oxygen :
[tex]\frac{2\times 16g/mol}{194 g/mol}\times 100=16.49\%[/tex]
