Chapter 10: Problem 22
Which of the following fluorides are sparingly soluble in water? (1) LiF (2) \(\mathrm{NaF}\) (3) CsF (4) KF
Short Answer
Expert verified
LiF is sparingly soluble in water.
Step by step solution
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Solubility Trends
When solving problems related to the solubility of compounds, it's essential to understand solubility trends. Solubility refers to how well a substance can dissolve in a solvent, like water. We often observe that certain compounds dissolve better than others. For example, the solubility of fluorides in water follows specific trends based on the size of the ions involved.
Generally, **fluorides of smaller alkali metals** tend to be less soluble in water. This happens because smaller ions pack more tightly in the crystal lattice, making it harder for water molecules to break it apart. To better understand these trends, we have to look at the alkali metals themselves, which leads us to our next core concept.
Generally, **fluorides of smaller alkali metals** tend to be less soluble in water. This happens because smaller ions pack more tightly in the crystal lattice, making it harder for water molecules to break it apart. To better understand these trends, we have to look at the alkali metals themselves, which leads us to our next core concept.
Alkali Metals
Alkali metals belong to Group 1 in the periodic table. These are:
The size of alkali metal ions plays a crucial role in determining the solubility of their fluoride compounds. From lithium to cesium, the ions increase in size:
- **Li** is the smallest.
- **Na** is larger than Li but smaller than K.
- **K** is larger than Na but smaller than Cs.
- **Cs** is the largest.
As the size of the alkali metal ion increases, the lattice energy of the fluoride decreases, making the compound more soluble in water. Thus, smaller alkali metals such as lithium form less soluble fluorides, like LiF, compared to larger alkali metals such as potassium forming more soluble fluorides, like KF.
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Cesium (Cs)
The size of alkali metal ions plays a crucial role in determining the solubility of their fluoride compounds. From lithium to cesium, the ions increase in size:
- **Li** is the smallest.
- **Na** is larger than Li but smaller than K.
- **K** is larger than Na but smaller than Cs.
- **Cs** is the largest.
As the size of the alkali metal ion increases, the lattice energy of the fluoride decreases, making the compound more soluble in water. Thus, smaller alkali metals such as lithium form less soluble fluorides, like LiF, compared to larger alkali metals such as potassium forming more soluble fluorides, like KF.
Fluoride Compounds
Fluoride compounds of alkali metals, such as LiF, NaF, KF, and CsF, exhibit varied solubility.
**Fluoride compounds** are combinations of an alkali metal and fluoride ion. The ability of these compounds to dissolve in water directly relates to the size of the alkali metal:
To sum up, the solubility of alkali metal fluorides increases as we move down the group from lithium to cesium. Therefore, in the context of our exercise, LiF is the most sparingly soluble fluoride.
**Fluoride compounds** are combinations of an alkali metal and fluoride ion. The ability of these compounds to dissolve in water directly relates to the size of the alkali metal:
- LiF: Due to lithium's small size, LiF has strong lattice energy making it sparingly soluble.
- NaF: Sodium is larger than lithium, so NaF is more soluble than LiF.
- KF: Potassium is even larger, making KF more soluble than NaF.
- CsF: Cesium, being the largest, results in CsF being the most soluble of all mentioned fluorides.
To sum up, the solubility of alkali metal fluorides increases as we move down the group from lithium to cesium. Therefore, in the context of our exercise, LiF is the most sparingly soluble fluoride.
