home > q&a board > chemistry > topic: buffer

Q BgQuestion:

Scholar
Karma Points: 200
Respect (100%):
posted by  boricua on 9/16/2008 2:30:09 AM  |  status: Live  

buffer

Course Textbook Chapter Problem
General Chemistry N/A N/A N/A
Question Details:
A buffer (at ph 5.0) containing potassium acetate is frequently used for isolation of plasmid DNA. If you have 3M solution of potassium acetate, how many moles of potassium acetate and acetic acid you need to make 500ml of the buffer.
Bonus Point Alert! Earn +4 additional karma points for helping this annual member.

AAnswers:

Answer Question
Guru
Karma Points: 2,074
posted by Xylene on 9/16/2008 2:58:58 AM  |  status: Live
Asker's Rating: Helpful   
boricua's comment:
"thanks a lot"
Response Details:
  pH = pKa + log [salt]/[acid]
 5.0 = 4.75 +  log [salt]/[acid]   ( pKa value of acetic is constant i.e 4.75)
 0.25  =   log [salt]/[acid]
  [salt]/[acid] = 1.7782
Here potassium acetate is salt and acetic acid is the acid  ( acidic buffer)
no. of moles of potassium acetate = 3 x 500/1000
                                                   = 1.5 moles
no. of moles of acetic acid = ?
  1.5/[acid] = 1.7782
  no. of moles of acetic acid = 0.8435
 
Answer Question
Ask New Question

Join Cramster's Community

Cramster.com brings together students, educators and subject enthusiasts in an online study community. With around-the-clock expert help and a community of over 100,000 knowledgeable members, you can find the help you need, whenever you need it. Join for free today » How Cramster is different from tutoring »

Need Help In

Useful Links