Problem 56 - A Complete Resource Book in Chemistry for JEE Main

Question

An organic compound on heating with \(\mathrm{CuO}\) produces \(\mathrm{CO}_{2}\), but not water. It may be (a) \(\mathrm{CH}_{4}\) (b) \(\mathrm{CCl}_{4}\) (c) \(\mathrm{CHCl}_{3}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}\)

Step-by-Step Solution

Answer

The compound is CCl_{4} .

Step 1: Understand the Reaction

The problem states that the organic compound produces CO_{2} when heated with CuO, but no water. This means that the compound must contain carbon but no hydrogen, as the absence of water ( H_{2}O ) indicates no hydrogen is present.

Step 2: Analyze Each Compound

Examine each chemical formula: (a) CH_{4} contains hydrogen, so it would produce water. (b) CCl_{4} contains no hydrogen, so it cannot produce water. (c) CHCl_{3} contains hydrogen, so it would produce water. (d) C_{2}H_{5}I contains hydrogen, so it would produce water.

Step 3: Determine the Correct Answer

Only CCl_{4} fits the criteria of producing CO_{2} without water since it has carbon but no hydrogen. This makes it the likely compound that reacts with CuO as described.

Key Concepts

Combustion Reactions

Combustion reactions are chemical processes where a substance combines with oxygen to release energy in the form of heat and light. This is typically seen as burning. Combustion reactions play a crucial role in chemistry and everyday life because they involve the conversion of chemical energy into heat energy.

In general, combustion of organic compounds always produces carbon dioxide ({CO_2} ) and water ({H_2O} ) if hydrogen is present. However, in the given exercise, the absence of water in the products indicates that no hydrogen is present in the compound being burned. This guides us to identify a compound like {CCl_4} that contains carbon but lacks hydrogen, thereby aligning with the outcome of producing only {CO_2} in the reaction.

Carbon Compounds

Carbon compounds are chemical substances composed of carbon atoms bonded with other elements. Carbon's ability to form four bonds makes it incredibly versatile, allowing it to form a wide variety of compounds. These compounds are integral to many fields, including organic chemistry. Understanding carbon compounds is significant because:

• They form the basis of all organic chemistry.
• They include everyday substances like sugars, fats, and proteins.
• Their diverse structures can influence their chemical properties and reactions.

In the context of the given exercise, distinguishing between carbon compounds such as {CH_4} , {CCl_4} , {CHCl_3} , and {C_2H_5I} relies on recognizing the presence or absence of hydrogen and other atoms connected to carbon, which influences their combustion reactions.

Chemical Analysis

Chemical analysis is the process used to identify the chemical composition and properties of a substance. It uses a variety of techniques and processes to uncover these characteristics. Identifying substances through chemical reactions, such as combustion, forms a key part of chemical analysis. In this exercise, the reaction involving (CuO) and the absence of water in the products is a method of analyzing the constituent elements of a compound. By evaluating the elements released during combustion, we can infer what elements were present in the original substance. This method allows us to deduce that a compound like {CCl_4} , which lacks hydrogen, will not produce water when combusted, compared to others like {CH_4} or {CHCl_3} , which contain hydrogen.

Hydrocarbons

Hydrocarbons are organic compounds comprising only hydrogen and carbon atoms. They're the simplest organic compounds and are classified into various types, including alkynes, alkenes, and alkanes based on the types of carbon-carbon bonds present. Hydrocarbons serve as the foundation for many more complex organic molecules and are primary components of fossil fuels:

• Alkanes, such as methane ({CH_4} ), are saturated hydrocarbons with single bonds.
• Alkenes and alkynes include double and triple bonds, respectively, adding to their reactivity.

In the exercise provided, we analyze hydrocarbons and similar compounds to identify their structure based on their reaction products. Completely hydrocarbon-based compounds, like {CH_4} , readily produce both {CO_2} and water upon combustion. By contrast, {CCl_4} is not a hydrocarbon, therefore the absence of hydrogen leads to unique product reactions when subjected to combustion.