I need to find the Kb of Analine. I've been told the ph is 8.81 and that the concentration of the solution is 0.1 mol/L. What would be the equation I'm working with :S ?
Aniline is an organic amine with a ring structure. Here is the way it looks.
(Broken Link Removed) It may be treated as a substituted ammonia just as methylamine was done a few days ago. We can write RNH2 for it.
RNH2 + HOH ==> RNH4^+ + OH^-
Do the ICE chart and go from there.
Does the R just represent a chain?
R represents a chain. Ar usually is used for the ring (technically an unsaturated ring such as as the benzene ring). Cyclohexane, for example, is an "R" group while benzene is an Ar group. So aniline would be ArNH2. I didn't use that at first because I didn't want to confuse you with the R and Ar bit.
Thanks :) I did the ice table but I don't know what to do from there. They haven't given me the Kb value so how do I find x? Or do I find the concentration of H+ from ph= -log[h+] and then divide it by 1 x 10^-14 to find the concentration on OH in the ice table?
wait I want to correct myself. I think I would subtract 8.81 from 14 to get the POH and then figure out the concentration of OH. Is this correct?
This is what I did:
pH = 8.81
pH + pOH = 14
pOH = 5.19
[OH-] = 10^-5.19
= 6.64 x 10^-6
__ArNH2 + HOH ==> ArNH4^+ + OH^-
I 0.1_____________O___________O
C -6.46 x 10^-6 +6.46 x 10^-6 +6.46 x 10^-6
E 0.1-6.46 x 10^-6 +6.46 x 10^-6 +6.46 x 10^-6
Kb = {6.46 x 10^-6)^2 / 0.1
= 4 x 10^-10
Yes, you are to calculate Kb. And you have approached the problem correctly; however, I have 4.17 x 10^-10. Your value for OH^- is ok although I left the extra digits in the calculator. I think your last operation may be where you lot the 0.17.
but would I keep one significant digit cause on the 0.1?
If it is 0.1 M aniline, you are correct, you keep only 1 s.f. and 4 is the one to keep. I am so used to students typing 0.1 when they see 0.100 that I jumped to conclusions and assume (aniline) to be 0.100, especially since you gave k to two places. Even then, howver, it would be 4.2 and not 4.17.
didn't I give K to one place :S 4 x 10^-10
I don't understand how it is 2 decimal places. 0.1 only has one signifca