Carius Method: Formula and Examples

The exact quantification of the presence of halogens in organic compounds is, hence, imperative in a myriad of applications in the intricate world of analytical chemistry. The Carius method, developed toward the end of the 19th century by the German chemist Georg Ludwig Carius, is one of the most reliable and accurate techniques for the same. The group of halogens includes fluorine, chlorine, bromine, and iodine—essential participants in many chemical reactions and vastly distributed within a large number of organic compounds: from pharmaceuticals to agrochemicals and industrial materials.

JEE Main 2025: Chemistry Formula | Study Materials | High Scoring Topics | Preparation Guide

JEE Main 2025: Syllabus | Sample Papers | Mock Tests | PYQs | Study Plan 100 Days

NEET 2025: Syllabus | High Scoring Topics |  PYQs

This Story also Contains

1. The Carius Method Explained
2. Types and Applications of the Carius Method
3. Implication in Real Life and Importance in Academics
4. Some Solved Examples
5. Conclusion

Knowledge of the concentration of halogens is essential not just for quality and safety but also in relation to environmental control and legislation connected with it. For instance, the high content of halogens in pharmaceuticals can impact their effectiveness and safety. In the environmental samples, halogens can indicate the level of pollution and hazardous substances. This technique by Carius unifies the quantification methods for those elements; thus, it becomes a very significant tool for a chemist or researcher.

The Carius Method Explained

One such method for quantitative analysis of organic compounds is the Carius method, which is used to establish how much halogens are contained in a substance. This includes fluorine, chlorine, bromine, and iodine.

This is achieved by heating a known mass of the organic compound with fuming nitric acid in the presence of silver nitrate, contained in a special type of glass tube called a Carius tube. Carbon and hydrogen from the compound are oxidized into carbon dioxide and water, respectively; while the halogen reacts with the silver nitrate to form a precipitate of silver halide.

Halogens

A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as a Carius tube, in a furnace. Carbon and hydrogen present in the compound are oxidized to carbon dioxide and water. The halogen present forms the corresponding silver halide (AgX). It is filtered, washed, dried, and weighed.

Let the mass of organic compound taken $=\mathrm{mg}$
Mass of AgX formed $=\mathrm{m}_1 \mathrm{~g}$
1 mol of AgX contains 1 mol of XMass of halogen in $\mathrm{m}_1 \mathrm{~g}$ of $\mathrm{AgX}=\frac{\text { atomic mass of } \mathrm{X} \times m_1 \mathrm{~g}}{\text { molecular mass of } \mathrm{AgX}}$

Percentage of halogen $=\frac{\text { atomic mass of } \mathrm{X} \times m_1 \times 100}{\text { molecular mass of } \mathrm{Ag} \mathrm{X} \times m}$

Sulphur

A known mass of an organic compound is heated in a Carius tube with sodium peroxide or fuming nitric acid. Sulfur present in the compound is oxidized to sulphuric acid. It is precipitated as barium sulphate by adding an excess of barium chloride solution in water. The precipitate is filtered, washed, dried, and weighed. The percentage of sulfur can be calculated from the mass of barium sulphate.

Let the mass of organic compound taken $=\mathrm{mg}$ and the mass of barium sulphate formed $=\mathrm{m}_1 \mathrm{~g}$ $1{\mathrm{~mol} \mathrm{of} \mathrm{BaSO}_4=233 \mathrm{~g} \mathrm{BaSO}}_4=32 \mathrm{~g}$ sulphur

$\begin{aligned} & \mathrm{m}_1 \mathrm{gBaSO}_4 \text { contains } \frac{32 \times m_1}{233} \mathrm{~g} \text { sulphur } \\ & \text { Percentage of sulphur }=\frac{32 \times m_1 \times 100}{233 \times m}\end{aligned}$

Types and Applications of the Carius Method

This method of Carius is used for the quantitative determination of the different halogens present in organic compounds.

It would be especially useful for the determination of the percentage of bromine since the precipitate of silver bromide formed during the reaction is easily filtered, washed, dried, and weighed. This can also be done for the determination of sulfur without the addition of silver nitrate. In this process, the sulfuric acid intermediate that is formed after the reaction of sulfur with fuming nitric acid gets precipitated as barium sulfate by the addition of barium chloride.

Implication in Real Life and Importance in Academics

There are several uses of the Carius method in many aspects.

In pharmaceutical industries, it is useful for checking the purity or quality of halogen-containing drugs. It can also be used in monitoring the existence of halogens in the metabolites of drugs. The method applies to environmental analysis for the determination of halogens in soil, water, and air samples. This application forms a basis for the evaluation of pollution levels and eventually meets environmental regulation requirements. In academic research, the Carius method is one of the cardinal techniques taught in undergraduate and graduate analytical chemistry classes since it ushers the student into quantitative analysis and eventually emphasizes the importance of measurement precision in chemistry.

Recommended topic video on (Carius Method )

Some Solved Examples

Example 1
Question:
In the Carius method, 0.099 g of a compound gave 0.287 g of AgCl. What is the percentage of chlorine in the compound?

1) 35.4%

2) 71.7% (correct)

3) 46.2%

4) 80.5%

Solution:

As we have learnt,

Carius method test for halogens -

percentage of $X=\frac{\text { Atomic mass } \times \mathrm{m}_1 \times 100}{\text { molecular mass of } \mathrm{AgX} \times \mathrm{m}}$

wherein,

$\mathrm{mI}_1=$ mass of AgX obtained
$m=$ mass of Organic compound taken
Therefore, \% of Chlorine is given by

$$=\frac{35.0}{143.5} \times \frac{0.287}{0.099} \times 100=71.7 \%
$$

Hence, the answer is the option (2).

Example 2
Question:
Which of the following is a FALSE statement?

1) The Carius method is used for the estimation of nitrogen in an organic compound. (correct)

2) The Carius tube is used in the estimation of sulfur in an organic compound.

3) Phosphoric acid produced on oxidation of phosphorus present in an organic compound is precipitated as Mg₂P₂O₇ by adding magnesia mixture.

4) Kjeldahl's method is used for the estimation of nitrogen in an organic compound.

Solution:
The Carius method is used for the estimation of halogens and sulfur in an organic compound, not for nitrogen. Therefore, the correct answer is Option (1).

Example 3
Question:
In the Carius method of estimation of halogen, 0.172 g of an organic compound showed the presence of 0.08 g of bromine. Which of these is the correct structure of the compound?

1) $\mathrm{CH}_3-\mathrm{Br}$
2) $\mathrm{C}_2 \mathrm{H}_5 \mathrm{Br}$
3) $\mathrm{C}_3 \mathrm{H}_7 \mathrm{Br}$ (correct)
4) $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{Br}$

Solution:

Given,

mass of organic compound = 0.172 gm

mass of Bromine = 0.08 gm

carius method mass $\%$ of ' $\mathrm{Br}^{\prime}=\frac{0.08}{0.172} \times 100=\frac{8000}{172}=46.51 \%$ option (1) mass $\%=\frac{80}{95} \times 100$
(2) mass $\%=\frac{2 \times 80 \times 100}{252}$
(3) mass $\%=\frac{1 \times 80 \times 100}{80+72+6+14}=\frac{8000}{172} \%$
(4) mass $\%=\frac{1 \times 80 \times 100}{109} \%$

Option (3) matches with the given mass percentage value

Therefore, Option 3 is correct.

Example 4

In the Carius method, a halogen-containing organic compound is heated with fuming nitric acid in the presence of :

1)HNO₃

2) (correct)AgNO₃

3)CuSO₄

4)BaSO₄

Solution

As we have learned,

In the Carius method, halogen-containing organic compounds are heated with fuming Nitric Acid in the presence of AgNO₃.

This is done to precipitate the halide ions in the form of AgX. The silver halides have very low Ksp values and have very low solubility.

Hence, the answer is the option (2).

Conclusion

In this respect, the Carius method has been a very important tool of analytical chemistry, offering a reliable and correct pathway for establishing the quantitative presence of halogens in an organic compound. Its application domains range from the industry to academic fields of activity. It is an instrumental technique for any professional or scientist working in very different fields of activity. In pharmaceuticals, it ensures the safety of the drug and its efficiency through its control of halogen content, while in environmental science, it helps in the detection of pollution and compliance with legislation related to it.