The Question is from neet-chemistry the-s-block-elements alkali-metals, and it was created by the author A.RAMA NAGESWARARAO

Question

Which of the following statements regarding the solubility of alkali metal carbonates is INCORRECT?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Solubility of ionic compounds
	**Related Topics**: Alkali metals, trends in the periodic table, lattice energy, hydration energy
	**Prerequisites**: Periodic trends, factors affecting solubility
## SOLUTION PATHWAY
**Given Information**:
	The question asks about the solubility trend of alkali metal carbonates.
**Method & Steps**:
	1. **Consider the factors affecting solubility:** Solubility of ionic compounds is determined by the balance between lattice energy (energy required to separate ions in the solid) and hydration energy (energy released when ions are hydrated by water molecules).
		Reasoning: A more negative lattice energy and a more negative hydration energy favor higher solubility.
	2. **Analyze the trend down the group:** As the size of the alkali metal cation increases down the group, the lattice energy decreases (due to the larger interionic distance). The hydration energy also decreases, but the decrease in lattice energy is more significant.
		Working: The charge density of the cation decreases down the group, leading to weaker attraction to both the carbonate anion and water molecules.
		Key Point: The decrease in lattice energy is the dominant factor affecting the solubility trend.
	3. **Determine the solubility trend:** Since the decrease in lattice energy outweighs the decrease in hydration energy, the solubility of alkali metal carbonates generally *increases* down the group.
		Result: The statement 'The solubility of alkali metal carbonates decreases down the group' is incorrect.
		Verification: This aligns with experimental observations, where $Li_2CO_3$ is less soluble than $Na_2CO_3$, $K_2CO_3$, $Rb_2CO_3$, and $Cs_2CO_3$.
## OPTION ANALYSIS
[A] ✓: The solubility of alkali metal carbonates generally increases down the group. This is the correct trend based on the interplay of lattice energy and hydration energy.
[B] :x: Lithium carbonate is less soluble than other alkali metal carbonates. This is a true statement, consistent with the increasing solubility trend down the group.
[C] :x: The solubility of alkali metal carbonates is influenced by the size of the cation. This is a true statement, as the cation size affects both lattice energy and hydration energy.
[D] :x: The solubility of alkali metal carbonates decreases down the group. This statement is incorrect, as explained above.
## LEARNING AIDS
	**Common Mistakes**:
		1. Focusing only on hydration energy: Considering only hydration energy would lead to the incorrect prediction that solubility decreases down the group. Remember to consider both lattice energy and hydration energy.
		2. Confusing solubility trends: Be careful not to confuse the solubility trends of different alkali metal compounds. For example, the solubility of alkali metal hydroxides increases down the group, while the solubility of alkali metal halides follows a more complex trend.
	**Quick Tips**:
		1. Remember the general trend: For alkali metal carbonates, the solubility generally increases down the group.
		2. Visualize the cation size: Larger cations have lower charge density, leading to weaker interactions and lower lattice energy, which ultimately influences the solubility trend.

A.RAMA NAGESWARARAO · Answer

The solubility of alkali metal carbonates generally increases down the group.

A.RAMA NAGESWARARAO · Answer

Lithium carbonate is less soluble than other alkali metal carbonates.

A.RAMA NAGESWARARAO · Answer

The solubility of alkali metal carbonates is influenced by the size of the cation.

A.RAMA NAGESWARARAO · Answer

The correct Option is "The solubility of alkali metal carbonates decreases down the group."

NEET Chemistry The S-Block Elements Alkali Metals MCQs

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