Qualitative Analysis Of Organic Compounds

A quantitative analysis is a way of determining the number of elements or molecules created during a chemical process. Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, and halogens make up organic compounds.

C and H detection

C and H are identified in a dry test tube by heating the chemical with CuO. They are both oxidised to CO₂ and H₂O. The existence of C and H is established if the CO₂ turns lime water milky and the H₂O turns anhydrous CuSO₄ blue.

Phosphorus Detection

The organic component is heated with an oxidising agent to help oxidise the phosphorus present in it to phosphate in order to determine the phosphorus. The solution is then heated with concentrated HNO₃ and treated with ammonium molybdate. The presence of phosphorus is then verified by the presence of a yellow precipitate.

The following reactions are involved in the process of estimating phosphorus methods:

Na₃PO₄ + 3HNO₃ → H₃PO₄ + 3NaNO₃

H₃PO₄ + 12(NH₄)₂MoO₄ + 21HNO₃ → (NH₄)₃PO₄.12MoO₃ + 21NH₄NO₃ + 12H₂O

Nitrogen Estimation

• The Dumas Method

Nitrogen is estimated using the Dumas technique, which involves heating a known quantity or weight of the component with copper oxide (CuO) in a carbon dioxide environment. This produces free Nitrogen, as well as carbon dioxide and water.

The following is the reaction:

C_xH_yNz + (2x+ 0.5y) CuO → xCO₂ + 0.5y H₂O + 0.5z (N₂) + (2x+ 0.5y)Cu

When the gases are passed over a heated copper gauge, tiny quantities of nitrogen oxides are converted to dinitrogen. The gaseous mixture is collected by passing it through a KOH solution, which absorbs carbon dioxide. Nitrogen is subsequently collected in the graduated tube’s top section.

• The Kjeldahl Method

In this procedure, a known quantity of an organic molecule, for example, 0.5 g, is heated in a Kjeldah’s flask with 10 g of potassium sulphate and 1 g of copper sulphate in 25 ml of sulphuric acid. Copper sulphate functions as a catalyst in this reaction, whereas potassium sulphate elevates the boiling point of concentrated sulphuric acid. The resulting combination combines with an excess of sodium hydroxide, resulting in the formation of ammonia. It is then treated with an excess of standard acid.

The following are the several reactions involved in the measurement of nitrogen using the Kjeldahl method:

C + H + S → CO₂ + H₂O + SO₂

N → (NH₄)₂SO₄

(NH₄)₂SO₄ + 2NaOH → Na₂SO₄ + 2NH₃ + 2H₂O

2NH₃ + H₂SO₄ → (NH₄)₂SO₄

The qualitative examination of organic compounds assists in detecting the presence or absence of a certain chemical.

FAQs

How is the Halogen Detection Test Performed in an Organic Compound?

A part of the fusion solution is acidified with dilute nitric acid. Excess silver nitrate solution is then added, and the formation of a precipitate shows the presence of halogens.

What is qualitative analysis?

The analysis of the species present in a particular substance is known as qualitative analysis. For example, if a compound is examined, the qualitative analysis would focus on identifying the elements and ions present rather than establishing how much of each is there.