Problem 164 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following Column-I Column-II (a) \(\mathrm{KHF}_{2}\) (p) Compound can exist (b) \(\mathrm{KHCl}_{2}\) (q) Compound is electrolyte in nature (r) Compound shows hydrogen (c) \(\mathrm{NF}_{3}\) bonding (d) \(\mathrm{PH}_{5}\) (s) Compound is non electrolyte (t) Compound can not exist.

Step-by-Step Solution

Answer

(a)-(p,q,r), (b)-(t), (c)-(p,s), (d)-(t)

Step 1: Analyzing Column I

Look at each compound in Column I to identify their properties and stability. (a) \( \mathrm{KHF}_2 \): A known compound, exists as a potassium bifluoride salt.(b) \( \mathrm{KHCl}_2 \): Such a compound would be unstable as it's not known in nature or lab practices.(c) \( \mathrm{NF}_3 \): An existing compound, known for its strong N-F bonds.(d) \( \mathrm{PH}_5 \): The compound is hypothetical and doesn't exist due to the instability of a pentavalent nitrogen in a small molecule.

Step 2: Matching Compound Existence

Match compounds based on their ability to exist.(a) \( \mathrm{KHF}_2 \) - (p) Compound can exist(b) \( \mathrm{KHCl}_2 \) - (t) Compound cannot exist(c) \( \mathrm{NF}_3 \) - (p) Compound can exist(d) \( \mathrm{PH}_5 \) - (t) Compound can not exist.

Step 3: Matching Electrolyte Properties

Determine whether the compounds are electrolytes or non-electrolytes.(a) \( \mathrm{KHF}_2 \): It dissociates in water, so it's (q) electrolyte in nature.(b) \( \mathrm{KHCl}_2 \): Hypothetical, thus doesn't apply.(c) \( \mathrm{NF}_3 \): Does not dissociate in water, so it is (s) non-electrolyte.(d) \( \mathrm{PH}_5 \): Hypothetical, thus doesn't apply.

Step 4: Matching Hydrogen Bonding

Identify compounds showing hydrogen bonding:(a) \( \mathrm{KHF}_2 \): Shows hydrogen bonding due to hydrogen fluoride, so it's (r) compound shows hydrogen bonding.(b) \( \mathrm{KHCl}_2 \): Hypothetical, doesn't apply.(c) \( \mathrm{NF}_3 \): Does not exhibit hydrogen bonding.(d) \( \mathrm{PH}_5 \): Hypothetical, doesn't apply.

Step 5: Final Matching Summary

Based on our analysis:(a) \( \mathrm{KHF}_2 \) matches (p), (q), and (r)(b) \( \mathrm{KHCl}_2 \) matches (t)(c) \( \mathrm{NF}_3 \) matches (p) and (s)(d) \( \mathrm{PH}_5 \) matches (t)

Key Concepts

Compound Stability

Understanding compound stability is crucial in chemistry. It describes whether a compound can exist or if it tends to decompose. When we say a compound is stable, we mean it can maintain its identity under normal conditions without breaking apart or reacting on its own.

A good example is the compound \(\mathrm{KHF}_2\), which exists as a stable salt known as potassium bifluoride. It does not decompose easily and can be found in various applications, such as in fluoridating water. In contrast, \(\mathrm{KHCl}_2\) is deemed unstable because we don't find it naturally or in practical laboratory scenarios. Therefore, it is considered theoretical, which means it cannot sustain its structure.

Another example is \(\mathrm{NF}_3\). This compound is stable due to the strong nitrogen-fluorine bonds. Lastly, we have \(\mathrm{PH}_5\), a theoretical compound because its structure would involve a pentavalent phosphorus, which is not feasible for smaller molecules. This inability is due to the strain and the unsuitable electron configuration that does not favor bonding.

Electrolyte Properties

Electrolytes are compounds that dissociate into ions when dissolved in water, making them capable of conducting electricity. This behavior is fundamental to many biological and chemical processes.

In the exercise, \(\mathrm{KHF}_2\) stands out as an electrolyte. When dissolved, it breaks into potassium \(\mathrm{K}^+\) and hydrogen fluoride \(\mathrm{HF}\) ions, allowing electricity to flow through the solution. The dissociation process is crucial because it enables many reactions in chemical and biological systems.

Contrastingly, compounds like \(\mathrm{NF}_3\) do not dissolve in water to form ions. Consequently, they cannot conduct electricity, categorizing them as non-electrolytes. Understanding which compounds can act as electrolytes helps chemists predict how substances will behave in solutions, affecting everything from battery function to nerve impulses in the body.

Hydrogen Bonding

Hydrogen bonding is a special type of interaction that often affects the properties of a compound, such as boiling and melting points. It occurs when a hydrogen atom, which is covalently bonded to an electronegative atom like nitrogen, oxygen, or fluorine, experiences attraction to another electronegative atom in a different molecule or part of the same molecule.

In the context of the exercise, \(\mathrm{KHF}_2\) illustrates hydrogen bonding. The presence of hydrogen fluoride in the compound allows \(\mathrm{H}\) to interact with the fluorine due to the high electronegativity of fluorine, forming a hydrogen bond. This type of interaction is why hydrogen fluoride exhibits a relatively high boiling point compared to other hydrogen halides.

However, \(\mathrm{NF}_3\) does not show hydrogen bonding because while nitrogen is electronegative, the molecular structure of \(\mathrm{NF}_3\) lacks hydrogen atoms that can participate in such interactions. Recognizing compounds capable of hydrogen bonding is vital to predicting their physical and chemical properties, such as solubility and volatility.