Ka and Kb

EMurphy_2L
Posts: 128
Joined: Sat Sep 07, 2019 12:16 am

Ka and Kb

so if Kb<10 -3 means it's a weak base, does Ka>10 3 mean it's a weak acid?

Alex Tchekanov Dis 2k
Posts: 118
Joined: Sat Aug 24, 2019 12:16 am

Re: Ka and Kb

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.

Benjamin Feng 1B
Posts: 102
Joined: Sat Sep 07, 2019 12:19 am

Re: Ka and Kb

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+

EMurphy_2L
Posts: 128
Joined: Sat Sep 07, 2019 12:16 am

Re: Ka and Kb

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?

vibha gurunathan 1h
Posts: 51
Joined: Mon Oct 07, 2019 12:15 am

Re: Ka and Kb

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.

Kayli Choy 2F
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

Re: Ka and Kb

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.

Alex Tchekanov Dis 2k
Posts: 118
Joined: Sat Aug 24, 2019 12:16 am

Re: Ka and Kb

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

BCaballero_4F
Posts: 94
Joined: Wed Nov 14, 2018 12:22 am

Re: Ka and Kb

It would be a strong acid instead of a weak acid

505306205
Posts: 97
Joined: Thu Jul 25, 2019 12:15 am

Re: Ka and Kb

If Ka is less than 10-3, then it is a weak acid. Greater than 10^3 would make it a strong acid.

Sara Richmond 2K
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

Re: Ka and Kb

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

Ayushi2011
Posts: 101
Joined: Wed Feb 27, 2019 12:17 am

Re: Ka and Kb

Greater than 10^3 is a strong acid.

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