Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: asigna on February 26, 2013, 12:03:24 AM

Title: need help with ph problems!!
Post by: asigna on February 26, 2013, 12:03:24 AM

What is the pH of a 0.25 M methylamine solution?

The formula is ch3nh2
so what I did was .25*2=.5
-log(.5)=.30

Calculate the pH of a 0.50 M solution of potassium cyanide

the formula is kcn
I did -log(.5)=.30



Am I doing this right? I feel that since these aren't strong acids/bases there should be more work involved

Title: Re: need help with ph problems!!
Post by: argulor on February 26, 2013, 12:17:20 AM

Quote from: asigna on February 26, 2013, 12:03:24 AM

Am I doing this right? I feel that since these aren't strong acids/bases there should be more work involved

I agree. Are you familiar with ICE tables?

The pK_b of methylamine is 3.36 and the pK_b of KCN is 3.00.