What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
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What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
Hi! Could someone please explain how to determine what acid is stronger when you are given pKa and Ka? As well as which base is stronger when you are given pKb and Kb?
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Re: What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
A stronger acid has a higher Ka value and a smaller pKa value. A stronger base has a higher Kb value and a smaller pKb value. If given a mixture of values, it would be easier to compare them to each other if they are converted to either all Ka values or all pKa values. Same for bases. That way, they are all being compared using the same measurement scale.
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Re: What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
When comparing Ka and pKa values, the higher the Ka value and the smaller the pKa value, the stronger the acid. On the other hand, the higher the Kb value and a smaller the pKb value, the stronger the base is. When comparing all Ka values or all pKa values (such as trying to rank them in order of strongest to weakest acids), the higher the Ka/Kb value, the stronger the acid, and the higher the pKa/pKb value, the stronger the base. Hope this answers your question!
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Re: What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
It is important to remember that pKa and Ka are inverses of each other. Same with pKb and Kb. So, the higher the value of Kb, the stronger the base. The higher value of pKb, the weaker the base. The reason this occurs is because pKa=-logKa (and same with pKb and Kb). So, if you are for example comparing a base with a pKb of 10 and a different base with a Kv of 4x10^-6, you should convert one of the values to the other and compare from them. For example, if you converted to pKb, you would compare the value of 10 to a value of -log*4.0x10^-6, or 5.4. Since the higher the pKb value the weaker the base, base 1 is weaker than base 2, as 10>5.4.
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Re: What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
A high Ka and Kb correlate to a stronger acid or base. pKa and pKb in a sense are inversely related to the strength of acids and bases, so a higher pKa or pKb indicates a weaker acid and base.
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Re: What does pKa, pKb, Ka, and Kb say about the strength of acids and bases.
A large Ka value means that the acid is strong. This also means that the pKa would be small. So Large Ka= Small pKa = strong acid.
A small Ka value means that the acid is weak. Also means pKa is large. So Small Ka = Large pKa = weak acid
The same would be for bases but switch Ka and pKa for Kb and pKb.
A small Ka value means that the acid is weak. Also means pKa is large. So Small Ka = Large pKa = weak acid
The same would be for bases but switch Ka and pKa for Kb and pKb.
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