Which of the following hydroxides is not an alkali?

Options

A. Ammonium hydroxide
B. Calcium hydroxide
C. Copper hydroxide
D. Sodium hydroxide

Answer

To determine which of the following hydroxides is not an alkali, we first need to understand the definition of an alkali. An alkali is a base that is soluble in water and produces hydroxide ions (OH-) when dissolved.

### Step-by-Step Solution:

1. **Identify the Hydroxides**: We have four hydroxides to consider:
- Ammonium hydroxide (NH4OH)
- Calcium hydroxide (Ca(OH)2)
- Copper hydroxide (Cu(OH)2)
- Sodium hydroxide (NaOH)

2. **Evaluate Ammonium Hydroxide**:
- Ammonium hydroxide dissociates in water to form NH4+ and OH- ions.
- Since it is soluble in water, ammonium hydroxide is classified as an alkali.

3. **Evaluate Calcium Hydroxide**:
- Calcium hydroxide dissociates in water to form Ca2+ and 2OH- ions.
- It is also soluble in water, making calcium hydroxide an alkali.

4. **Evaluate Copper Hydroxide**:
- Copper hydroxide does not dissolve well in water. It is considered a weak base and is insoluble in water.
- Therefore, copper hydroxide does not qualify as an alkali.

5. **Evaluate Sodium Hydroxide**:
- Sodium hydroxide dissociates in water to form Na+ and OH- ions.
- It is highly soluble in water, thus it is classified as an alkali.

6. **Conclusion**:
- Among the given hydroxides, copper hydroxide is the only one that is not an alkali because it is insoluble in water.

### Final Answer:
The hydroxide that is not an alkali is **Copper Hydroxide (Cu(OH)2)**.

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