What do you understand by the estimation of elements? Discuss breifly a method for the estimation of carbon and hydrogen in an organic compound.
Estimation of elements. Estimation of elements means to determine the percentage composition of each element present in the organic compound.
Estimation of carbon and hydrogen (Liebig’s method): A known weight of the organic compound is strongly heated with an excess of dry copper oxide in an atmosphere of dry and pure oxygen or air. Carbon of the compound is oxidised to carbon dioxide and hydrogen to water.
Water vapours and carbon dioxide are bubbled through weighed U-tube containing anhydrous calcium chloride and weighed potash bulbs containing a strong solution of potassium hydroxide. The increase in mass of U-tube gives the mass of water formed and increase in mass of potash bulbs gives the mass of carbon dioxide formed. Knowing the masses of water and carbon dioxide formed, the percentage of hydrogen and carbon can be calculated.
Calculations:
Let the mass of organic compound taken = Wg
Let the mass of water formed = a g
(increase in mass of anhydrous CaCl2 U- tube)
Let the mass of carbon dioxide formed = bg
(increase in mass of potash bulbs)
(i) Percentage of hydrogen.
18 g of water contains hydrogen = 2g
(ii) Percentage of carbon.
44 g of carbon dioxide contains carbon = 12 g
Thus percentage of carbon
