Estimation of sulphur:
A known mass of the organic substance is heated strongly with fuming HNO3. C & H get oxidized to CO2& H2O while sulphur is oxidized to sulphuric acid as per the following reaction.
The resulting solution is treated with excess of BaCl2 solution H2SO4 present in the solution in quantitatively converted into BaSO4, from the mass of BaSO4, the mass of sulphur and hence the percentage of sulphur in the compound can be calculated.
A known mass of the organic compound is taken in clean carius tube and added a few mL of fuming HNO3. The tube is the sealed. It is then placed in an iron tube and heated for about 5 hours. The tube is allowed to cool to temperature and a small hole is made to allow gases produced inside to escape. The carius tube is broken and the content collected in a beaker. Excess of BaCl2 is added to the beaker H2SO4 acid formed as a result of the reaction is converted to BaSO4. The precipitate of BaSO4 is filtered, washed, dried and weighed. From the mass of BaSO4, percentage of S is found.
Mass of the organic compound = w g
Mass of the BaSO4 formed = x g
233g of BaSO4 contains 32 g of Sulphur
In an estimation of sulphur by carius method, 0.2175 g of the substance gave 0.5825 g of BaSO4 calculate the percentage composition of S in the compound.
Weight of organic compound 0.2175 g
Weight of BaSO4 0.5825 g
233 g of BaSO4 contains 32 g of S