Question

I need to know the pH (for each) based on the Ka and Kb values given:

Acid…………….Ka

HCN………4.0*10^-10
HOCl……..2.95*10^-8

Base……………Kb

C5H5N…………2.9*10^-9
HONH2…………9.1*10^-9

Answer 1

@seehearcreate are you good with pH calculations?

Answer 2

Yep! Okay, so take the negative log of the acid conc. to find the pH. For the bases, since its pOH, you need to do the same but then take that answer and subtract it from 14(:

Answer 3

do you mind setting one up so I can see? I'm struggling

Answer 4

for the first one HCN
ka = 4.0 * 10^-10
then
pH = - log ( ka)

for base as @seehearcreate says its pOH
then find pOH = -log(Kb)
pH + pOH = 14

Answer 5

ok I got 4.6 is that right @thushananth01

Answer 6

oh wait hold up

Answer 7

9.4?? @seehearcreate

Answer 8

Let me calculate them, hold on. @thushananth01 that's what I was saying about the bases and pOH.

Answer 9

Is the 5.4 M HOCl pH=7.5

Answer 10

9.39
7.53

Oh wait, I see what you're saying that it says Kb.

Forget about subtracting. Hold on, let me get the bases.

Answer 11

Thank you so much

Answer 12

Ok so I was on the right track. Now for C5H5N is it 5.46

Answer 13

No, I was wrong, since it's already calculated values for Kb. You'd wouldn't be trying to find the H concentrations but the OH. So, the values are just regular -log(OH-)

So it would be 8.53 and 9.04. You'll always know it's not a base if the pH is below 7. That's an acid.

Answer 14

Ok are those HOCl and HCN? @seehearcreate

Answer 15

Yup!

Answer 16

Ok sweet. HOCl= 8.53
HCN= 9.04
the bases are…?
I got
C5H5N= pH 5.46
HONH2

Answer 17

@seehearcreate

Answer 18

sorry, I just wanna make sure I got this

Answer 19

Hold on, none of these values are coming back correctly.

Answer 20

Are you sure you have the acids and bases under the right values? they seem backwards.

Answer 21

yeah

Answer 22

Well I'm not sure then. I'm a little busy since I'm trying to finish up my classes before exams tomorrow, so I'll try to get someone else for you.

@abb0t

Answer 23

no worries I completely understand, thank you! @seehearcreate