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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: 911mutley on May 13, 2010, 10:45:25 AM

Title: weak base
Post by: 911mutley on May 13, 2010, 10:45:25 AM

Hi Guys

If trying to find the pH of a weak base, how is the figure for the concentration of water (reactant) needed as well as the equilibrium concentration of the other reactant and a value for K.

Can anyone help?

Thanks

Title: Re: weak base
Post by: Borek on May 13, 2010, 11:18:58 AM

Ignore water concentration, it is assumed to be constant and already included in the Kb value.

Title: Re: weak base
Post by: 911mutley on May 13, 2010, 12:05:03 PM

Even if the figure is given it should still be ignored?

Title: Re: weak base
Post by: Borek on May 13, 2010, 12:39:50 PM

Show the question in question.

Title: Re: weak base
Post by: aeacfm on May 16, 2010, 05:05:33 AM

to the pH of weak base or weak acid suppose :

B + H₂O  ::equil:: BH + OH^-
here we can  determine the pH by calculating [OH^-] by the following equation
 
K = X² / 1-X

where X  is the concentration of OH^- ion   & K is the dissociation constant of the base
 by solving the euation you can determine the pH
the final thing here is that the concentration of water is ignored as it is the general solvent found every where in the solution so its voncentration is ignored