A sample was analysed in a mass spectrometer. The mass spectrum produced shows that the molar mass of the compound was 56 g mol^-1. What is its molecular formula?
A sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32 g of water and the carbon was oxidised to 3.23 g of carbon dioxide.
The mass of the sample of organic compound extracted from the plant is assumed to have carbon and hydrogen. When it is burned in oxygen, the mass of water produced is 1.32 g and the mass of carbon dioxide produced is 3.23 g.
Water consists up of one atom of oxygen and 2 atoms of hydrogen, with the fractional mass of hydrogen given as 2/18.
1.32 g of water has 1.32*2/18 g of hydrogen.
Carbon dioxide consists of one atom of carbon and 2 atoms of oxygen with the fractional mass of carbon given as 12/44
3.23 g of carbon dioxide has 3.23*12/44 g of carbon.
The integral ratio of the number of moles of carbon to the number of moles of hydrogen in the compound is 0.073/0.1466 = 1/2
This gives the empirical formula of the organic compound as CH2.
The molar mass of the compound was found to be 56 g/mole. This gives the molecular formula as C4H8.