In chemistry Quantitative analysis is a method used in the determination of percentage composition of elements present in an organic compound. In this article, you will learn how to estimate halogens in an organic compound by Carius method.
Estimation of halogens by Carius method
● A known mass of the compound is heated with fuming nitric acid (HNO3) and silver nitrate (AgNO3) taken in a hard glass tube known as Carius tube in a furnace.
● Since nitric acid is the strong oxidizing agent, carbon and hydrogen present in the given compound oxidized to carbon dioxide and water respectively.
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● The halogen present in the compound reacts with silver nitrate to form silver halide AgX. This method is not suitable for fluorine (F). because silver fluoride is soluble in water, hence precipitate of silver fluoride is not formed.
● The precipitate of silver halide is then filtered, washed, dried and weighted.
How to calculate % of halogen in the compound
Consider an organic compound having mass M grams. The halogen present in given organic compound is chlorine.
As mentioned above, chlorine present in the compound reacts with silver nitrate to form silver chloride. Consider the mass of silver chloride formed is m grams.
As we know the molecular mass of silver chloride is 143.5 grams. hence 143.5 grams of silver chloride contains 35.5 grams of chlorine. then m grams of silver chloride contains x grams of chlorine.
Therefore m grams of silver chloride (AgCl) will contain (m × 35.5) / 143.5 grams of chlorine (Cl).
Hence M grams of an organic compound will contain (m × 35.5) / M × 143.5 grams of chlorine (Cl).
Therefore 100 grams of an organic compound will contain (m × 35.5× 100) / M × 143.5 percentage of chlorine (Cl).