# Chemistry

posted by .

What stoichiometric concentration of the indicated substance is required to obtain an aqueous solution with the pH value shown below?
aniline (C6H5NH2) for PH of 9.05

I converted pH to pOH so pOH=4.98
[OH-] =1.122*20^-5

C6H5NH2 + H2O --------> C6H5NH3+ + OH-
I: a N/A 0 0
C: -x N/A +x +x
E: a-x N/A x x

Kb=[C6H5NH3+][OH-]/[C6H5NH2 ]
4.2*10^-10 = x^2/(a-x)

Substituting in the equilibrium values from the ICE table and rearranging I found "a" which is the concentration of C6H5NH2 to be 0.299M but this is the wrong answer. Does anyone know what I did wrong?

• Chemistry -

The only thing I can find is that if pH = 9.05 then pOH is 4.95 and not 4.98 which makes (aniline) = 0.2997 which I would round to 0.300M. I assume you are using Kb found in your text or notes. My OLD OLD text lists it as 3.98E-10 but you should go with the number in your text or notes. The correct answer is 0.300M. See my solution a couple posts above yours under Ashley. It looks almost the same as yours except for the pOH thing.

• Chemistry -

On second thought I do know what the problem is. You have only two significant figures in Kb; therefore, the answer must have no more than two. So the answer should be rounded to 0.03M
Let me know is this is correct. I think that must be the problem.

• Chemistry -

No, that didn't work. I even tried using your Kb value but that still wasn't right.

• Chemistry -

I made a typo in my response (transposed the numbers). The concn we calculated is 0.298 or so and to two s.f. that rounds to 0.30 (not 0.03 as I posted in my second post). I think 0.30 will get it for you. I would appreciate a new post to DrBob222 since this one is getting buried.
Surely 0.30 is right.

• Chemistry DrBob222 -

No, 0.30 isn't right either. I'm going to ask my prof about it tomorrow.

## Similar Questions

1. ### Chemistry

A 10g sample of aniline hyrdochloride is dissolved in 250 mL of solution. C6H5NH2-HCl(s) => C6H5NH3+ (aq)+ Cl-(aq) H2O is shown over the arrow. What is the pH of the solution?
2. ### Chemistry

How do I do this?? Calculate the pH at the equivalence point for the titration of 0.20 M aniline (C6H5NH2, Kb = 3.8 x 10-10) with 0.20 M HCl. [Hint: remember the dilution factor caused by addition of titrant to the aniline solution.]
3. ### chemistry

What stoichiometric concentration of the indicated substance is required to obtain an aqueous solution with the pH} value shown below?
4. ### Chemistry

Complete this table of values for four aqueous solutions at 25 °C. Solution A: [H+]=0.0093M [OH-]=?
5. ### Chemistry

Each value below represents a different aqueous solution at 25 °C. Classify each solution as acidic, basic, or neutral. pH=9.72 pOH=4.69 pOH=13.62 [H+]=7.5e-2 [H+]=7.8e-9 [H+]=1e-7 [OH-]=4.5e-12 [OH-]=3.5e-5 pH=4.09 pOH=7
6. ### Chemistry

Complete this table of values for four aqueous solutions at 25 °C. Solution A: [H+]=0.0093M [OH-]=?
7. ### Chem

What stoichiometric concentration of the indicated substance is required to obtain an aqueous solution with the pH value shown below?
8. ### Chemistry

A solution of aniline(C6H5NH2, Kb=4.2x10^-10) has a pH of 8.69 at 25 Celsius. What was the initial concentration of aniline?
9. ### Chemistry

Sometimes the basicity of a solution is reported using pOH (pOH = -log[OH-]). What is the a. [OH-] if pOH = 1.90 b. [H3O+] if pOH = 12.94 c. pH if pOH = 9.70
10. ### chemistry

Sometimes the basicity of a solution is reported using pOH (pOH = -log[OH-]). What is the a. [OH-] if pOH = 1.90 b. [H3O+] if pOH = 12.94 c. pH if pOH = 9.70

More Similar Questions