Ammonium hydroxide is a weak base because
A) it is a dilute solution.
B) it is only slightly soluble in water.
C) it cannot hold on to its hydroxide ions.
D) it dissociates only slightly in water.
E) it is completely ionized in aqueous solution.
The correct answer and explanation is :
The correct answer is D) it dissociates only slightly in water.
Explanation:
Ammonium hydroxide (NH₄OH) is considered a weak base because it dissociates only slightly in water. When ammonium hydroxide is dissolved in water, it undergoes partial dissociation to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻). The dissociation reaction is as follows:
[
NH₄OH \rightleftharpoons NH₄⁺ + OH⁻
]
In the case of a weak base, this reaction does not go to completion; instead, it reaches an equilibrium. Only a small fraction of the ammonium hydroxide molecules dissociate into ions, meaning most of the molecules remain in their undissociated form in the solution. As a result, the concentration of hydroxide ions in the solution is relatively low, leading to a weaker basicity compared to a strong base like sodium hydroxide (NaOH), which dissociates completely in water.
Let’s analyze the other options:
- A) It is a dilute solution: A dilute solution refers to the concentration of the base, but this does not explain why ammonium hydroxide itself is a weak base. Even if it were concentrated, ammonium hydroxide would still be a weak base because it dissociates only partially.
- B) It is only slightly soluble in water: Ammonium hydroxide is actually quite soluble in water. The weakness of the base is due to partial dissociation, not its solubility.
- C) It cannot hold on to its hydroxide ions: This is misleading. Ammonium hydroxide does hold onto its hydroxide ions, but it only dissociates partially, meaning fewer hydroxide ions are present in the solution compared to a strong base.
- E) It is completely ionized in aqueous solution: This statement is true for strong bases but not for weak bases. Ammonium hydroxide is not completely ionized in aqueous solution.
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