What is the pKa of sodium ethoxide?
The Correct Answer and Explanation is:
Correct Answer: The pKa of sodium ethoxide (specifically, the conjugate acid ethanol) is approximately 16.
Explanation:
Sodium ethoxide (NaOCH₂CH₃) is the sodium salt of ethanol. It is a strong base commonly used in organic chemistry, especially in elimination (E2) and condensation reactions. However, when we talk about the pKa of sodium ethoxide, we are actually referring to the pKa of its conjugate acid, which is ethanol (CH₃CH₂OH).
The pKa of ethanol is about 16, meaning that ethanol is a weak acid. This also tells us something important about sodium ethoxide: since its conjugate acid has a high pKa value, sodium ethoxide itself is a strong base. In acid-base chemistry, a high pKa means a weak acid, and therefore, its conjugate base (in this case, ethoxide ion) must be relatively strong.
To understand this better, consider the equilibrium:
CH₃CH₂OH ⇌ CH₃CH₂O⁻ + H⁺
This equilibrium lies far to the left because ethanol does not give up its proton easily. As a result, its conjugate base, ethoxide ion (CH₃CH₂O⁻), has a strong tendency to grab protons, making it a good base.
Sodium ethoxide exists as a salt: Na⁺ CH₃CH₂O⁻. The sodium ion does not directly influence the acidity or basicity of the compound; it simply balances the charge of the ethoxide ion. What makes sodium ethoxide useful is the ethoxide ion’s reactivity.
In summary, the pKa of sodium ethoxide refers to the pKa of ethanol, which is about 16. This value tells us that sodium ethoxide is a strong base, suitable for many types of deprotonation reactions in organic synthesis.
