Question

Pyridine contains carbon, hydrogen, and nitrogen. A 0.546 g sample was burned to produce 1.518 g of carbon dioxide and 0.311 g of water. Determine the empirical formula of pyridine.

Answer 1

let in compound number of moles of C, H and O be x, y and z respectively

Number of moles of CO2 = mass of CO2 / molar mass CO2

= 1.518/44

= 0.0345

Number of moles of H2O = mass of H2O / molar mass H2O

= 0.311/18

= 0.017278

Since 1 mol of CO2 has 1 mol of C

Number of moles of C in CO2= 0.0345

so, x = 0.0345

Since 1 mol of H2O has 2 mol of H

Number of moles of H = 2*0.017278 = 0.034556

mass N = total mass - mass of C and H

= 0.546 - 0.0345*12 - 0.034556*1

= 0.097444

number of mol of N = mass of O / molar mass of O

= 0.097444/14

= 0.00696

so, z = 0.00696

Divide by smallest to get simplest whole number ratio:

C: 0.0345/0.00696 = 5

H: 0.034556/0.00696 = 5

O: 0.00696/0.00696 = 1

So empirical formula is:C5H5N