Question

How can I calculate the mass percent of carbon, nitrogen and oxygen in caffeine, C8H10N4O2.

Answer 1

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:

`8(12.01g)+10(1.008g)+4(14.007g)+2(15.999g)=96.08g+10.08g+56.028g+31.998g=194.186g`

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

`(96.08g)/(194.186g)= 0.49478=49.48`

Carbon = 49.48%

Nitrogen: 56.028g

`(56.028g)/(194.186g)=0.28853=28.85`

Nitrogen = 28.85%

Oxygen: 31.998g

`(31.998g)/(194.186g) =0.16478=16.48`

Oxygen = 16.48%

Answer 2

Step-by-step explanation:

Molecular mass of carbon caffeine(
`C_8H_(10)N_4O_2`), = 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:

`\frac{\text{Number of atoms of element}* \text{Atomic mass of element}}{\text{molecular mass of compound}}* 100`

Percentage of carbon:

`(8* 12 g/mol)/(194 g/mol)* 100=49.48\%`

Percentage of hydrogen:

`(10* 1g/mol)/(194 g/mol)* 100=5.15\%`

Percentage of nitrogen:

`(4* 14 g/mol)/(194 g/mol)* 100=28.86\%`

Percentage of oxygen :

`(2* 16g/mol)/(194 g/mol)* 100=16.49\%`