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

Question

An organic compound on heating with 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 \( \text{CCl}_4 \) (carbon tetrachloride).

Step 1: Understand the reaction requirement

The organic compound produces \( \text{CO}_2 \) but not water when heated with CuO. This means the compound must contain carbon but not hydrogen.

Step 2: Analyze each compound

Examine each option to determine their elements: - \( \text{CH}_4 \) (methane) contains both C and H.- \( \text{CCl}_4 \) (carbon tetrachloride) contains only C and Cl.- \( \text{CHCl}_3 \) (chloroform) contains C, H, and Cl.- \( \text{C}_2 \text{H}_5 \text{I} \) (ethyl iodide) contains C, H, and Iodine.

Step 3: Identify eligible compound

Since the compound must not contain hydrogen, only \( \text{CCl}_4 \) (carbon tetrachloride) fits the requirement. It contains carbon but no hydrogen, so it can produce \( \text{CO}_2 \) without forming water.

Key Concepts

Organic Compounds

Organic compounds are a wide category of chemicals mainly made from carbon atoms. Carbon's ability to form stable bonds with many elements, including itself, is why so many organic compounds exist.
Usually, these compounds also contain other elements such as hydrogen, oxygen, nitrogen, sulfur, and halogens (like chlorine and iodine).
The unique feature of carbon is its tetravalency, which means each carbon atom can form four covalent bonds with other atoms.

• This allows the formation of long chains, branched structures, and rings.
• Common examples include hydrocarbons like methane (\(\text{CH}_4\)), and compounds with halogens such as carbon tetrachloride (\(\text{CCl}_4\)).

Understanding these compounds is crucial for grasping how our exercise looks at chemical reactions, especially when exploring which elements are present or absent and the behavior of these elements when heated with a reagent like CuO.

CuO Reaction

The reaction involving copper(II) oxide (CuO) is an important aspect of our exercise. CuO is often used as an oxidizing agent in organic chemistry.
When we heat an organic compound with CuO, it often helps in showing the presence or absence of certain elements.
During our exercise, CuO reacts with the carbon part of the compound to form carbon dioxide (\(\text{CO}_2\)). But for water (\(\text{H}_2\text{O}\)) to form, hydrogen must be present in the compound:

• If a compound contains hydrogen, like methane or ethyl iodide, it would typically produce water when heated with CuO along with \(\text{CO}_2\).
• However, if a compound lacks hydrogen, such as carbon tetrachloride,\(\text{CO}_2\)will be produced without water.

By understanding this reaction, we're able to identify which compounds might yield specific products.

Oxidation Reactions

Oxidation reactions involve the addition of oxygen or the removal of hydrogen from a substance. In our context, when organic compounds are oxidized, particularly with CuO, these reactions can result in the production of carbon dioxide and, if hydrogen is present, water.
In oxidation, each element has its oxidation state, which determines how electrons are gained or lost:

• In the oxidation of compounds like carbon tetrachloride (\(\text{CCl}_4\)), only carbon is oxidized, forming carbon dioxide, since no hydrogen is available to create water.
• For compounds with hydrogen, both carbon and hydrogen interact with oxygen, leading to the formation of\(\text{CO}_2\)and\(\text{H}_2\text{O}\).

By examining these oxidation reactions, we can determine the presence or absence of elements like hydrogen that impact chemical reactions involving CuO.