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Ka and Kb

Posted: Thu Jan 23, 2020 1:24 pm
so if Kb<10 -3 means it's a weak base, does Ka>10 3 mean it's a weak acid?

Re: Ka and Kb

Posted: Thu Jan 23, 2020 1:26 pm
You can think about it like this. K is the products over reactants, so therefore anytime the reactants are waayyyyyyyy more than the products it is weak, more specifically when the ratio makes the K value less than 10^-3. This is regardless if it's an acid or base.

Re: Ka and Kb

Posted: Thu Jan 23, 2020 1:27 pm
The 2 constants would have the same inequality. If either Kb or Ka is weak, then the value should be less than 10^-3. Looking at the equation,

Ka = [H+][A-]/[HA], so the smaller Ka, is, the less it dissociates and the lower the concentration of H+

Re: Ka and Kb

Posted: Thu Jan 23, 2020 1:28 pm
Alex Tchekanov Dis 2k wrote:You can think about it like this. K is the products over reactants, so therefore anytime the reactants are waayyyyyyyy more than the products it is weak, more specifically when the ratio makes the K value less than 10^-3. This is regardless if it's an acid or base.

so Ka>10 3 is a strong acid?

Re: Ka and Kb

Posted: Thu Jan 23, 2020 1:29 pm
Ka greater than 10^3 signifies a strong acid.

Ka = [CB][H+]/ [HA]

The more the acid (HA) dissociates, the more H+ is produced. This increases the Ka because the concentration of the products increases. If the Ka is greater than 10^3, that means it dissociates a lot, making it a strong acid and not a weak one.

Re: Ka and Kb

Posted: Thu Jan 23, 2020 2:27 pm
Additionally, the greater the Ka, the smaller the pKa, and the stronger the acid. The greater the Kb, the smaller the pKb, and the stronger the base.

Re: Ka and Kb

Posted: Mon Jan 27, 2020 3:52 pm
EMurphy_2L wrote:
Alex Tchekanov Dis 2k wrote:You can think about it like this. K is the products over reactants, so therefore anytime the reactants are waayyyyyyyy more than the products it is weak, more specifically when the ratio makes the K value less than 10^-3. This is regardless if it's an acid or base.

so Ka>10 3 is a strong acid?

Yes exactly, and since it is a strong acid, it will have a weak conjugate base

Re: Ka and Kb

Posted: Mon Jan 27, 2020 5:55 pm
It would be a strong acid instead of a weak acid

Re: Ka and Kb

Posted: Mon Jan 27, 2020 8:53 pm
If Ka is less than 10-3, then it is a weak acid. Greater than 10^3 would make it a strong acid.

Re: Ka and Kb

Posted: Tue Jan 28, 2020 12:22 pm
Remember that Kb corresponds to bases and Ka corresponds to acids so it can be difficult to compare. First consider that K is [Products]/[Reactants]. So anytime K is very very small it means that there are way more reactants than there are products thus the solution is very weak. This reasoning works for both the Ka and Kb value "regardless of whether it is an acid or base".
Examples=
Ka= 10^3 Strong Acid
Ka=10^-3 Weak Acid
Kb= 10^3 Strong Base
Kb= 10^-3 Weak Base

Re: Ka and Kb

Posted: Thu Jan 30, 2020 3:59 pm
Greater than 10^3 is a strong acid.