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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: govibe on January 06, 2008, 06:20:31 PM

Title: buffers problem
Post by: govibe on January 06, 2008, 06:20:31 PM

"Calculate the pH after 0.020 mol NaOH is added to 1.00 L of each of the following solutions.

    (a) 0.480 HONH2 (Kb = 1.1x10-8)
    (b) 0.480 M HONH3Cl
    (c) a mixture containing 0.480 M HONH2 and 0.480 M HONH3Cl"

for (a), the reaction, the dissociation is HONH2+ H2O --->>> H4ON+ + OH- ??
The ICE box is like

HONH2+ H2O --->>> H4ON+ + OH-
0.480M                     0         0.02
-x                            +x        +x

so the Kb=1.1E-8 = (0.02+x)x/(0.480-x)

so x is 2.64E-7, so OH- concentration is 0.02+2.64E-7=0.02. The negative log of that is 1.7, and 14-1.7 is 12.30, is that correct? Do I have to do a stoichiometry equation in eddition to an ICE box?

for parts b and c, I'm not sure the dissociation of HONH3Cl is...

Title: Re: buffers problem
Post by: Borek on January 06, 2008, 06:57:12 PM

So your main problem is whether hydroxylamine is basic or acidic... It is basic, it can get protonated like ammonia.

Title: Re: buffers problem
Post by: govibe on January 06, 2008, 07:37:15 PM

what does the salt HONH3Cl dissociate into?