Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

KF combines with HF to form \(\mathrm{KHF}_{2} .\) The compound contains the species (a) \(\mathrm{K}^{+}, \mathrm{F}^{-}\)and \(\mathrm{H}^{+}\) (b) \(\mathrm{K}^{+}, \mathrm{F}^{-}\)and \(\mathrm{HF}\) (c) \(\mathrm{K}^{+}\)and \(\left[\mathrm{HF}_{2}\right]^{-}\) (d) \([\mathrm{KHF}]^{+}\)and \(\mathrm{F}_{2}\)

Step-by-Step Solution

Answer

The correct species for KHF2 is (c) \( \mathrm{K}^{+} \) and \( \left[\mathrm{HF}_{2}\right]^{-} \).

Step 1: Understand the composition of KHF2

The formula for the compound is \( \mathrm{KHF}_{2} \), which signifies that the compound is made up of potassium (K), hydrogen (H), and two fluorine (F) atoms.

Step 2: Identify ions of the compound

Potassium (K) commonly forms a positive ion \( \mathrm{K}^{+} \). In compounds, fluorine typically forms a negative ion \( \mathrm{F}^{-} \), and the presence of hydrogen with fluorine often indicates the formation of hydrofluoric acid (\( \mathrm{HF} \)). However, in this compound, the fluorine and hydrogen form a unique complex \( \left[\mathrm{HF}_{2}\right]^{-} \).

Step 3: Determine possible ion combinations within KHF2

Given the ions identified, \( \mathrm{K}^{+} \) will pair with the complex \( \left[\mathrm{HF}_{2}\right]^{-} \) to maintain charge balance (a charge of +1 and -1 respectively), resulting in the ionic compound being \( \mathrm{K}^{+} \) and \( \left[\mathrm{HF}_{2}\right]^{-} \).

Step 4: Compare options with derived ions

Now compare the ionic pairing \( \mathrm{K}^{+} \) and \( \left[\mathrm{HF}_{2}\right]^{-} \) to the provided options: (a), (b), (c), (d). The correct species that matches our determined ions is provided in option (c).

Key Concepts

Ionic Compounds

Ionic compounds are a type of chemical compound consisting of positive and negative ions. These ions attract each other due to opposite electrical charges, forming a neutral compound. In the realm of inorganic chemistry, ionic compounds play a crucial role.
Ions can form from either one or more elements donating or accepting electrons. For instance, in the compound \(\text{KHF}_2\), we tend to see potassium turning into a positive ion \(\text{K}^+\) by losing an electron. On the other hand, fluorine accepts an electron to form a negative ion \(\text{F}^-\). When these ions come together, we get stable ionic bonds through their electrostatic attraction.
Here’s why ionic compounds are fascinating:

• They usually have high melting and boiling points because the ions are strongly bonded together.
• In their solid state, they form crystalline lattices, which are structured and starkly regular at the atomic level.
• When dissolved in water or melted, ionic compounds conduct electricity as the ions are free to move.

Understanding ionic compounds not only helps in grasping the structure of substances but also their chemical reactions and properties.

Chemical Species

The term 'chemical species' refers to atoms, molecules, ions, or radicals of the same chemical identity. In essence, these are entities in chemical reactions. In any given chemical reaction or process, identifying the chemical species involved is paramount.
For instance, in the compound \( \text{KHF}_2 \), the species include \( \text{K}^+ \), \( \text{F}^- \), and the unique chemical species \( \left[\text{HF}_2\right]^- \). These are all distinct chemical species, each playing a role in the compound's overall properties.
A clear understanding of chemical species helps in:

• Identifying changes that occur during a chemical reaction.
• Predicting the properties and possible reactions of a compound.
• Recognizing the internal and external forces acting upon compounds in chemical reactions.

In simplistic terms, recognizing chemical species is like identifying the players on a football team; each has its vital role and contribution to the whole 'game' of chemistry.

Complex Ions

Complex ions are fascinating entities in the field of inorganic chemistry. They are formed when simple ions composed of metal ions coordinate with one or more ions or neutral molecules, also known as ligands. These ligands donate electron pairs to the metal ion.
In \( \text{KHF}_2 \), the complex ion \( \left[\text{HF}_2\right]^- \) is formed. This unique ion consists of two fluorine atoms and one hydrogen, where the hydrogen forms a bond with two fluorine atoms, showcasing a property called hydrogen bonding.

• Such complex ions often display unique properties, such as colors and magnetic characteristics, due to their electronic structures.
• They play a significant role in biological systems, such as the way hemoglobin carries oxygen in blood.
• They're also important in industrial applications, being used in catalysis and materials science.

Understanding complex ions allows chemists to create and manipulate compounds with desired properties and functionalities, enhancing both theoretical and applied chemistry.