Homework Help Forum: chemistry

Posted by millie on Wednesday, October 7, 2009 at 9:20pm.

a buffer composed of 0.50mol acetic acid and 0.50mol sodium acetate is diluted to a volume of 1.0L. The pH of the buffer is 4.74. How many moles of NaOH must be added to the buffer solution to increase its pH to 5.74?

• chemistry - DrBob222, Wednesday, October 7, 2009 at 9:48pm

  I assume you are using pKa = 4.74 so that pH = 4.74 + log 0.5/0.5 = = 4.74 + log 1 = 4.74 + 0 = 4.74. If we call acetic acid HAc and the acetate ion (the base) Ac, then To make the pH 5.74 we calculate the B/A as follows: 5.74 = 4.74 + log B/A You can go through the calculation but you should end up with (Ac)/(HAc) = 10 Then we write the equation HAc + NaOH = NaAc + H2O HAc = 0.5 to start Ac = 0.5 to start. We add x moles NaOH. The HAc after the reaction will be 0.5 - x and the Ac will be 0.5+x Just plug those values into the (Ac)/(HAc) = 10 and solve for x. I always like to put that value in and resolve the equation to see if I get 5.74. Post your work if you get stuck.

  
  

• chemistry - millie, Wednesday, October 7, 2009 at 10:07pm

  thanks for your help, it worked out :)

  
  

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