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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: laddoo12 on February 28, 2012, 06:39:03 PM

Title: weak acid and salt of weak acid in a solution :S
Post by: laddoo12 on February 28, 2012, 06:39:03 PM

A solution containing 0.10 M HA (a weak acid) and 0.20 M NaA (the salt of the weak acid) has a pH = 3.30. What is the pH after 25 mmol of HCl is added to 500 mL of this solution?

no clue how to do it i worked backwards with the ph to find the ka

3.3=pka+log(.2/.1) and so on but thats where i got stuck...the answer to the question is PH=3

can someone tell me what steps i should take to solve this problem :S

Title: Re: weak acid and salt of weak acid in a solution :S
Post by: Borek on February 29, 2012, 04:05:39 AM

Quote from: laddoo12 on February 28, 2012, 06:39:03 PM

3.3=pka+log(.2/.1)

Just solve for pKa, this is the only unknown in the equation.