Posted by Kyo on Friday, October 22, 2010 at 6:33pm.
Estimate the equilibrium constant for the weak base (CH3)2NH, if a 1.59×10-2 M aqueous solution of (CH3)2NH has a pOH 2.58 (make an exact calculation assuming that initial concentration is not equal to the equilibrium concentration).
(CH3)2NH + H2O = (CH3)2NH2+ + OH-
I know how to calculate it if initial concentraton = equilibrium concentration...but how are you suppose to calculate it if they aren't?
- Chem - DrBob222, Friday, October 22, 2010 at 9:03pm
I've not seen a problem like this and I'm not sure exactly what it means; however, I think I would try
Keq = [(CH3)2NH2^+)][OH^-]/[(CH3)2NH)]
and plug in (0.00263)^2 for the numerator. For the denominator I would substitute 0.0159 and NOT subtract the OH^- from it (which it would have at equilibrium). However, I don't see that as an exact calculation and I don't understand talk of an exact calculation when the problem starts by saying estimate.
- Chem - Kyo, Friday, October 22, 2010 at 9:23pm
Does the .00263 come from antilog (-2.58)?
If so, I plugged it into my calculator and got .00275.
That was the method I initially used (.00275^2)/.0159 and I got 4.35 x 10^-4
but that answer was wrong.
The answer is suppose to be 5.21 x 10^-4.
Thank you for trying though. =]
- Chem - DrBob222, Friday, October 22, 2010 at 10:19pm
OK. Yes, that's how I obtained 0.00263 but I just checked and that's the antilog of -2.58 so I suggest you check your calculator again. If you get a different number, perhaps you should look into a new calculator. ;-). The 5.21 number you get by
(0.00263)^2/(0.0159-0.00263) = ?? which is the exact way of doing things; but that is what it is at equilibrium. I'm still confused by the wording of the problem.
- Chem - Kyo, Friday, October 22, 2010 at 11:34pm
Ohh. I just tried a similar problem and used the equilibrium way and it was right...
Thank you so much for your help!
Answer This Question
More Related Questions
- CHEM - Calculate the equilibrium constant for the weak base CH3NH2, if a ...
- Chemistry - Estimate the equilibrium constant for the weak acid HCN, if a 4.68×...
- chemistry - Calculate the equilibrium constant for the weak base C5H5N, if a ...
- chemistry - Estimate the equilibrium constant for the weak acid HCO2H, if a 2.19...
- Chemistry - I wrote the dissociation or ionization in water for each of the ...
- Chemistry - I would appeciate any help with identifying the chiral carbons, if ...
- chem - Arrange the following amines in order of decreasing base strength. NH3, ...
- Chemistry - It is difficult to type these but I'll do my best. This is the first...
- chemistry - Calculate the pH of a 0.35 M solution of dimethylamine, (CH3)2NH.
- chem - what is the balanced equation for ozone gas reacts with 2,3,4,5-...