How does Ka/pKa and Kb/pKb relate to acid/base strength?? (1 Viewer)

[SadCeliac]

Question in title

I've always just assumed that the lower pKa is the stronger the acid, and the higher pKb is the stronger the base - similar to pH. But I think there's a better way to explain this in a exam - could yall please help??

Thanksss

 

[nsw..wollongong]

high Ka = strong acid. Low pKa = strong acid. think of it like [H+] concentration vs pH, high H conc = low pKa

 

[SadCeliac]

high Ka = strong acid. Low pKa = strong acid. think of it like [H+] concentration vs pH, high H conc = low pKa

Ohhh okay okay tysm

And what does it actually represent though (Ka - I mean)

Like is it just how easily the acid dissociates??

 

[nsw..wollongong]

yep exactly right, the higher the Ka the more readily it dissociates which makes sense for strong acids compared to weak acids and fml i just realised i got a question on that wrong in my trials

 

[SadCeliac]

yep exactly right, the higher the Ka the more readily it dissociates which makes sense for strong acids compared to weak acids

hang on but strong acids completely dissociate.... I thought they don't have a Ka

fml i just realised i got a question on that wrong in my trials

that sucks rip

 

[nsw..wollongong]

hang on but strong acids completely dissociate.... I thought they don't have a Ka


that sucks rip

huh no they have like rlly rlly high Ka values

 

[SadCeliac]

huh no they have like rlly rlly high Ka values

but... isn't Ka based on the acid dissociation equilibrium.... and something like HCl doesn't form an equilibrium because it fully ionises and dissociates completely?????


help

 

[nsw..wollongong]

but... isn't Ka based on the acid dissociation equilibrium.... and something like HCl doesn't form an equilibrium because it fully ionises and dissociates completely?????


help

WHAT
i think ur mixing it up with something else

Ka = how readily sum disociates
high Ka = disociates so readily its crazy = strong acid
strong acid = HCl = dissociates completely into H+ and Cl- = therefore the high Ka is justified
HCl ≠ equilibrium rxn

 

[nsw..wollongong]

high Ka doesnt mean equilibrium bc Ka isnt a measure of eq, u generally use Ka equations for weak acids because they don't completely disocciate so u cant just plug the [H+] value into -log[H+] to get the pH, if that makes sense. but u can do that with strong acids.

so for weak acids = use Ka equation (products over reactants)
strong acids = u don't need to, just use -log formula to find pH

 

[SadCeliac]

WHAT
i think ur mixing it up with something else

Ka = how readily sum disociates
high Ka = disociates so readily its crazy = strong acid
strong acid = HCl = dissociates completely into H+ and Cl- = therefore the high Ka is justified
HCl ≠ equilibrium rxn

okay okay fine yes that makes sense.

nah im lost i just googled and this came up
vs

HUH

 

[SadCeliac]

high Ka doesnt mean equilibrium bc Ka isnt a measure of eq, u generally use Ka equations for weak acids because they don't completely disocciate so u cant just plug the [H+] value into -log[H+] to get the pH, if that makes sense. but u can do that with strong acids.

so for weak acids = use Ka equation (products over reactants)
strong acids = u don't need to, just use -log formula to find pH

yeah okay fair enough - so EVERY ACID/BASE forms an equilibrium, just strong ones do it completely and super readily, so they have a really high Ka and Kb... okay okay

 

[SadCeliac]

ok got it

 

[nsw..wollongong]

okay okay fine yes that makes sense.

nah im lost i just googled and this came up
View attachment 39169 vs View attachment 39170

HUH
View attachment 39171

listen u need to look at the Ka in conjunction with other acid values
HCl is in the top 5 in terms of Ka values of acids, so that within itself denotes that its a strong acid

nonetheless, u don't need to know why HCl has that Ka value
all u need to know is that if they give u a Ka value in the question, know that ur dealing with a weak acid
if they don't and u have a weak acid in the question, know that u have to do either an ice table or use products/reactants bc u cant just use the regular log formula to find pH

 

[SadCeliac]

listen u need to look at the Ka in conjunction with other acid values
HCl is in the top 5 in terms of Ka values of acids, so that within itself denotes that its a strong acid

nonetheless, u don't need to know why HCl has that Ka value
all u need to know is that if they give u a Ka value in the question, know that ur dealing with a weak acid
if they don't and u have a weak acid in the question, know that u have to do either an ice table or use products/reactants bc u cant just use the regular log formula to find pH

yeah thats what ive been doing the whole time, its just i was confused at first because I didn't realise strong acids also have an equilibrium

mb tysm

 

[nsw..wollongong]

strong acids also have an equilibrium

well... no, but yes
just say they go to completion

 

[SadCeliac]

well... no, but yes
just say they go to completion

will do

 

[synthesisFR]

I Ain’t reading all this but isn’t ur exam tmrw

 

[SadCeliac]

I Ain’t reading all this but isn’t ur exam tmrw

like yeh but im just consolidating - trust i know all this

 

[SadCeliac]

like yeh but im just consolidating - trust i know all this

its that time to make sure i havent forgotten anything and am just going hyper over every little bit in the exam in front of me rn

 

[nsw..wollongong]

ull be fine, dont stress urself out too much bc ur gonna overthink everything tmr