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Quantitative analysis

May 4, 2013

Introduction to Quantitative analysis:

Once we have known the various elements present in any organic compound, the next point of interest is to know how much of each element is present in the compound. Determination of the relative proportions generally as percentage of various elements present in an organic compound is called quantitative analysis of that compound. For quantitative analysis the percentage of the various elements present in any compound are estimated by suitable chemical methods.

Quantitative analysis:

Estimation of carbon and hydrogen:

A known weight of the organic compound is strongly healed with excess of dry copper oxide in an atmosphere of dry and pure oxygen or air. Carbon of the composite is oxidised to carbon and hydrogen to water.

C + 2CuO `->`   CO2 `uarr` + Cu

2H + CuO `->` H2O `uarr` Cu

The CO2 and H2O are absorbed by a strong solution of caustic potash and anhydrous calcium chloride respectively. The percentage of carbon and hydrogen is calculated from the weights of CO2 and H2O obtained. These weights are obtained by finding the weights of caustic potash and calcium chloride tubes before and after the experiment.


Estimation of Oxygen:

Oxygen is commonly estimated by the method of difference. The proportion of all other fundamentals are added jointly and then subtracted from 100.

Estimation of nitrogen (Kjeldahl method):

This technique is base scheduled the information to various nitrogenous organic compounds while heated with con. H2SO4 are quantitatively analysis transformed into ammonium sulphate. The ammonium sulphate thus acquire is heated with overload NaOH and the ammonia liberated is absorbed in an identified volume of standard acid.


From the volume of standard acid used by ammonia and the mass of organic compound taken for the experiment we can calculate the mass of nitrogen in the compound.

Organic compound  `stackrel(H_2SO_4)(->)` (NH4)2

SO4 `stackrel(NaOH)(->)` NH3 `stackrel(H_2SO_4)(->)` (NH4)2 SO4

With nitrogen

Estimation of sulphur:

A recognized mass of the organic compound is heated in a preserved tube with fuming acid. The sulphur there in the organic compound will be oxidized to sulphuric acid. The tube is frozen and broken down in dilute hydrochloric acid. Then excess of barium chloride solution is supplementary. The impulsive of barium sulphate acquire is filtered, washed, dried and weighted precisely.



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