Ka vs Kb Weak Acids: Acetic Acid Low Ka, Lower Kb?

Thread starter UMath1
Start date Mar 23, 2016
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Acid base Acids Equilibrium Weak

In summary, Ka and Kb are equilibrium constants used to measure the strength of a weak acid or base. Acetic acid is considered a weak acid because it does not fully dissociate in water, resulting in a lower concentration of hydronium ions and a lower acidity. The low Ka value of acetic acid also makes it a weaker acid compared to others. Similarly, the low Kb value of acetic acid affects its basicity, making it a weaker base compared to others.

Mar 23, 2016

UMath1

Since Acetic Acid is a weak acid, it has a low Ka which means that the forward reaction is not favored as much as the reverse reaction. However, the Kb is even lower than the Ka...how is this possible? Shouldn't the Kb be higher to indicate that the reverse reaction is favored?

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Mar 23, 2016

Borek

Mentor

Kb is not a property of the acid, but of the conjugate base.

FAQ: Ka vs Kb Weak Acids: Acetic Acid Low Ka, Lower Kb?

What is the difference between Ka and Kb for weak acids?

Ka and Kb are equilibrium constants that measure the strength of a weak acid or base. Ka measures the strength of an acid in terms of its ability to donate a proton, while Kb measures the strength of a base in terms of its ability to accept a proton.

Why is acetic acid considered a weak acid?

Acetic acid is considered a weak acid because it does not completely dissociate in water. Instead, only a small percentage of the molecules dissociate into ions. This results in a lower concentration of hydronium ions in solution, making it a weaker acid compared to strong acids like hydrochloric acid.

How does the low Ka value of acetic acid affect its acidity?

The lower the Ka value of an acid, the weaker it is. Acetic acid has a Ka value of only 1.8 x 10^-5, which means it is a weaker acid compared to other acids with higher Ka values. This means that acetic acid is less likely to donate a proton in solution, resulting in a lower acidity.

Why is Kb lower than Ka for acetic acid?

Kb is lower than Ka for acetic acid because it is a weaker base compared to its conjugate acid, acetate. This means that acetic acid is more likely to accept a proton from water to form its conjugate base, resulting in a lower Kb value.

How does the low Kb value of acetic acid affect its basicity?

Similar to Ka, the lower the Kb value of a base, the weaker it is. Acetic acid has a Kb value of only 5.6 x 10^-10, which means it is a weaker base compared to other bases with higher Kb values. This means that acetic acid is less likely to accept a proton in solution, resulting in a lower basicity.