Question

Phosphorus is estimated by Carius Method as magnesium pyrophosphate.
A.True
B.False

Answer 1

Hint: In this method an organic compound of known mass containing phosphorus is heated with fuming nitric acid which leads to the formation of phosphoric acid which is then precipitated as magnesium-ammonium phosphate by adding magnesia mixture. This precipitate is then dried and ignited to get magnesium pyrophosphate.

Complete answer:
Carius Method is an analytical method in which the known mass of an organic compound is heated with fuming nitric acid in a sealed carius tube in which carbon gets converted to carbon-dioxide and hydrogen converts into water. The phosphorus present in the compound is then oxidized to phosphoric acid. This phosphoric acid is then precipitated as magnesium-ammonium phosphate by adding magnesia mixture which contains $Mg C {{l} {2}}, N {{H} {4}} Cl $ and ammonia. The precipitate formed is then washed, dries and ignited to get magnesium pyrophosphate. The percentage of phosphorus can be calculated by knowing the mass of the organic compound used and the formed magnesium pyrophosphate. So, the given statement is true.

Hence, the correct choice is (A).

Note:
 There is also an alternative method to estimate phosphorus by the Carius Method; this is done by precipitating phosphoric acid to ammonium phosphomolybdate by heating it with concentrated nitric acid and then adding ammonium molybdate. This method can also be used to estimate sulfur. The presence of halogens is also determined in organic compounds as halogens form sodium halide on fusion with sodium metal which can be easily extracted and identified.
The mass of phosphor is determined from the mass of precipitate formed and the mass of a known organic compound. The precipitate must be washed, filtered, dried and weighed properly.