Problem 8 - A Complete Resource Book in Chemistry for JEE Main

Question

Carbon and hydrogen are estimated by (a) Leibig method (b) Duma's method (c) Carius method (d) Kjeldahl's method

Step-by-Step Solution

Answer

The correct answer is (a) Leibig method.

Step 1: Understanding the Problem

We need to determine which methods from the options provided are used to estimate carbon and hydrogen in compounds.

Step 2: Review Each Option

(a) Leibig method: Known for estimating carbon and hydrogen in organic compounds. (b) Duma's method: Primarily used for nitrogen estimation. (c) Carius method: Used for the determination of halogens and sulfur in organic compounds. (d) Kjeldahl's method: Commonly used for nitrogen estimation.

Step 3: Identify the Correct Answer

The Leibig method (option a) is the correct choice as it is specifically designed for estimating carbon and hydrogen content in organic compounds.

Key Concepts

Liebig Method

The Liebig Method, named after the German chemist Justus von Liebig, is a classical technique used for estimating the content of carbon and hydrogen in organic compounds. This method forms the basis of modern analytical organic chemistry. In this process, the organic compound is completely burned in the presence of excess oxygen. The resulting carbon dioxide and water produced are then measured. The amount of these substances allows us to determine the amount of carbon and hydrogen originally present in the compound. Key steps in the Liebig Method:

• Combustion: The sample is burned in the presence of excess oxygen.
• Carbon Dioxide Collection: The carbon in the compound forms carbon dioxide, which is absorbed in a strong alkali solution.
• Water Collection: The hydrogen in the compound forms water, which is collected and weighed.

The precise measurement of carbon dioxide and water enables the accurate estimation of carbon and hydrogen in the original compound. This method has been pivotal in the advancement of organic chemistry by providing a reliable means to analyze elemental composition.

Estimation of Carbon

Carbon estimation in organic compounds is a crucial process that helps chemists understand the structure and composition of substances. Using the Liebig Method, the carbon content is determined by measuring the carbon dioxide produced when the substance is burned.To calculate the amount of carbon:- Calculate the weight of carbon dioxide formed by using the reaction: \( \text{Carbon in compound} + \text{Excess oxygen} \rightarrow \text{Carbon Dioxide} \)- From the mass of carbon dioxide, calculate the carbon content using the formula: \[\text{Weight of Carbon} = \left(\frac{12}{44}\right) \times \text{Mass of } CO_2\] This formula arises from the molar mass ratio of carbon \(12\) to carbon dioxide \(44\).The Liebig Method provides accurate carbon measurements, which are crucial for formulating molecular formulas and understanding chemical properties.

Estimation of Hydrogen

Estimating hydrogen in organic compounds is another essential aspect of understanding molecular composition, and the Liebig Method is effectively used for this purpose. During the combustion of an organic compound:- Hydrogen reacts with oxygen to form water.- The formation of water from hydrogen can be expressed as: \[\text{Hydrogen in compound} + \text{Oxygen} \rightarrow \text{Water}\]To find the hydrogen content:

• Collect the water produced and measure its mass.
• Determine the hydrogen mass using: \[\text{Weight of Hydrogen} = \left(\frac{2}{18}\right) \times \text{Mass of } H_2O\] Here, the ratio of the molar masses of hydrogen \(2\) to water \(18\) is used.

Understanding the hydrogen content helps in constructing the empirical formula of the compound, facilitating deeper insights into its chemical nature.