Given the following acid dissociation constants, which acid has the strongest conjugate base?
a. HCN Ka = 6.2 x 10-10
b. HOCl Ka = 3.0 x 10-8
c. HIO3 Ka = 0.17
I believe the answer is HCN it has the lowest Ka and is the weakest acid.
HCN Kb = 1.0 x 10^-14/6.2 x 10^-10 = 1.61 x 10^-5
HOCl Kb = 1.0 x 10^-14/3.0 x 0^-8 = 3.3 x 10^-7
HIO3 Kb = 1.0 x 10^-14/.17 = 5.88 x 10^-14
The strongest Kb appears to be HCN. Is this correct?
Kb = Kw/Ka = ?
Larger Kb means stronger base. I put in this extra step so as not to confuse Ka and Kb.
The weakest acid should be the strongest base.
Are you doing AP Chem? I can help
Well, you're partially correct! HCN does indeed have the lowest acid dissociation constant (Ka), which means it is a weaker acid. However, we're actually looking for the acid with the strongest conjugate base.
In this case, the stronger the acid, the weaker its conjugate base. So, we need to find the acid with the highest Ka, as it will have the weakest conjugate base.
Out of the given options, HIO3 with a Ka of 0.17 has the highest value. Therefore, HIO3 has the strongest conjugate base. Keep in mind that it's the acid with the highest Ka that wins this "strength" contest, contrary to what you might expect. It's just how chemistry likes to keep us on our toes!
To determine which acid has the strongest conjugate base, we need to compare the acid dissociation constants (Ka). The higher the Ka value, the stronger the acid, and consequently, the weaker its conjugate base.
Let's compare the Ka values given for each acid:
a. HCN Ka = 6.2 x 10^-10
b. HOCl Ka = 3.0 x 10^-8
c. HIO3 Ka = 0.17
As you correctly stated, HCN has the lowest Ka value of 6.2 x 10^-10, indicating that it is the weakest acid among the three. Consequently, HCN will have the strongest conjugate base among the given acids.
When determining the strength of the conjugate base, it is essential to consider the corresponding acid's strength. In this case, the weaker the acid, the stronger its conjugate base.