Problem 13 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Choose the incorrect formula out of the four compounds for an element X below :[Main Online April 11, 2015] (a) \(\mathrm{X}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{X}_{2} \mathrm{Cl}_{3}\) (c) \(\mathrm{X}_{2}\left(\mathrm{SO}_{4}\right)_{3}(\mathrm{~d}) \mathrm{XPO}_{4}\)

Step-by-Step Solution

Answer

Option (b) \(\mathrm{X}_2 \mathrm{Cl}_3\) is the incorrect formula.

Step 1: Analyze the given formulas

Examine the chemical formulas of the compounds given in the options: - (a) \(\mathrm{X}_2 \mathrm{O}_3\) - (b) \(\mathrm{X}_2 \mathrm{Cl}_3\)- (c) \(\mathrm{X}_2\left(\mathrm{SO}_4\right)_3\)- (d) \(\mathrm{XPO}_4\)

Step 2: Determine valency assumptions for element X

Assume element \(\mathrm{X}\) has a valency that allows it to form possible compounds with each of the given type of anions or oxygen. X should have different valencies for oxide, chloride, sulfate, and phosphate.

Step 3: Check consistency with common valencies

- For oxide (option a): Typically, metals may show +3 oxidation state to form \(\mathrm{X}_2 \mathrm{O}_3\), which matches common oxidation states.- For chloride (option b): \(\mathrm{X}_2 \mathrm{Cl}_3\) suggests \(\mathrm{Cl}\) is -1, \(\mathrm{X}\) should also have +3, which is uncommon in combination with chloride (usually not seen for common metals).- For sulfate (option c): \(\mathrm{SO}_4^{2-}\) indicates that \(\mathrm{X}\) is +3 here, which is consistent.- For phosphate (option d): \(\mathrm{PO}_4^{3-}\) suggests \(\mathrm{X} = +3\), which is also consistent.

Step 4: Identify the incorrect formula

The compound \(\mathrm{X}_2 \mathrm{Cl}_3\) (option b) is incorrect because it suggests an unusual valency of \(\mathrm{X}\) that usually doesn't form with chlorine in real-world chemistry. Chlorine generally forms compounds where the other element shows a +1 or +2 valency (e.g., \(\mathrm{XCl}\) or \(\mathrm{XCl}_2\)). These compounds are uncommon.

Key Concepts

Understanding Chemical Formulas

Chemical formulas represent the composition of a chemical compound. Each element is represented by its chemical symbol, and the quantity of each atom is indicated by a subscript. For example, in the formula \(\mathrm{X}_2 \mathrm{O}_3\), the element "\(\mathrm{X}\)" appears twice, and oxygen "\(\mathrm{O}\)" appears three times.

Chemists use these formulas to understand how atoms are bonded in a compound and the ratio in which they are combined. This is essential because the properties of a compound are determined by both its type and ratio of elements.

Moreover, recognizing the correct chemical formula is crucial for solving chemistry problems as it directly correlates with the quantitative and qualitative analysis of chemical reactions. Always double-check formulas to ensure accuracy.

Valency Determination and its Significance

Valency is a concept that helps explain how elements combine. It's the measure of an element's combining power with other atoms when it forms chemical compounds or molecules. In simple terms, it's the number of electrons an atom can gain, lose, or share.

To find valency, always look at how an element forms compounds. For instance, oxygen usually has a valency of -2, meaning it needs two more electrons to create stable compounds such as \(\mathrm{X}_2 \mathrm{O}_3\). Elements commonly follow specific valencies, which is why understanding these helps predict compound formation.

For element "X," if it forms \(\mathrm{X}_2 \mathrm{O}_3\), it should have a +3 valency, balancing the -2 valency of oxygen. These consistencies help in determining the correctness of chemical formulas. An unusual valency or uncommon combination often signals an incorrect formula as noted in the solution for \(\mathrm{X}_2 \mathrm{Cl}_3\).

Inorganic Compounds in Chemistry

Inorganic compounds are typically compounds that lack carbon-hydrogen bonds, unlike organic components. These compounds play a critical role in numerous biological and chemical processes.

Common inorganic compounds include oxides, sulfates, and chlorides. Each follows general formation rules based on the typical valency of their constituent elements. For example, \(\mathrm{X}_2\mathrm{O}_3\) is an oxide where "X" must balance with oxygen's valency to form a stable compound. Similarly, \(\mathrm{X}_2 (\mathrm{SO}_4)_3\) is a sulfate showing internal consistency with typical valencies.

Understanding these are essential in chemistry because predicting reactions and compound formations can be tied back to how well one knows these common types. Inorganic chemistry often relies on recognizing these patterns, helping in identifying unusual or incorrect formulas, just like discerning the incorrectness of \(\mathrm{X}_2 \mathrm{Cl}_3\) in theoretical exercises.