7.
Among the following salts which has the highest water solubility?
a. NaClO4
b. CsClO4
c. LiClO4
d. KClO4
Which Perchlorate Salt Has Highest Water Solubility: NaClO4, CsClO4, LiClO4, or KClO4?
Lithium perchlorate (LiClO4) exhibits the highest water solubility among NaClO4, CsClO4, LiClO4, and KClO4 due to its optimal hydration energy balance. Solubility depends on lattice energy versus hydration energy for these alkali metal perchlorates. NaClO4 follows closely, while KClO4 and CsClO4 show much lower solubility.
Option Analysis
Solubility trends reverse the typical alkali metal pattern because perchlorate’s large anion minimizes lattice energy differences, emphasizing cation hydration.
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LiClO4: Small Li⁺ ion yields high hydration energy (~59.8 g/100 mL at 25°C), exceeding lattice energy for maximum solubility.
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NaClO4: Larger Na⁺ reduces hydration slightly (~209 g/100 mL at 25°C), still highly soluble but less than LiClO4.
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KClO4: Further decreased hydration (~1.7-2 g/100 mL at 20°C), low solubility overall.
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CsClO4: Largest Cs⁺ has weakest hydration (~1.97 g/100 mL at 25°C), least soluble.
Answer: c. LiClO4
Lithium perchlorate (LiClO4) stands out as the perchlorate salt with the highest water solubility among NaClO4, CsClO4, LiClO4, and KClO4, crucial for competitive exams like CSIR NET Life Sciences and chemistry. This anomaly arises from hydration energy dominating over lattice energy in Group 1 perchlorates.
Solubility Data Comparison
| Salt | Solubility (g/100 mL at ~25°C) | Key Factor |
|---|---|---|
| LiClO4 | 59.8 | Highest hydration energy |
| NaClO4 | 209 | High but less than Li |
| KClO4 | ~1.7-2 | Low hydration |
| CsClO4 | 1.97 | Lowest hydration |
Why LiClO4 Tops Solubility
Small Li⁺ ions attract water strongly, while large ClO₄⁻ weakens lattice energy differences down the group, inverting the solubility order: LiClO4 > NaClO4 > KClO4 > CsClO4. This explains its use in batteries and solvents, unlike sparingly soluble KClO4 in pyrotechnics.
