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- Apr 17, 2009
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Hi, TBR gave this formula for determining the pH of weak reagents. I'm just having trouble understanding it. What I'm having trouble with is it telling me when I can or cannot use this equation.
pH = 1/2 pKa - 1/2 log [HA]
Here is what the book says. According to equation increasing [HA] lowers the pH. Stronger acids have more dissociation, so they should form solutions of a lower pH.
So they use this to find pH of a weak acid correct?
Here is a example problem
What is the pH of 1.00 M HF with pKa = 3.32?
answer: 1.66
Here is the solution.
*** it gave 2 requirements that I'm having trouble understanding
1) the weak acid concentration must be greater than Ka
2) pKa must lie between 2 and 12.
BOTH of these creteria are met??
Can someone explain to me how these 2 criteria are met.. I'm so horrible at this part of Acid and base
pH = 1/2 pKa - 1/2 log [HA]
Here is what the book says. According to equation increasing [HA] lowers the pH. Stronger acids have more dissociation, so they should form solutions of a lower pH.
So they use this to find pH of a weak acid correct?
Here is a example problem
What is the pH of 1.00 M HF with pKa = 3.32?
answer: 1.66
Here is the solution.
*** it gave 2 requirements that I'm having trouble understanding
1) the weak acid concentration must be greater than Ka
2) pKa must lie between 2 and 12.
BOTH of these creteria are met??
Can someone explain to me how these 2 criteria are met.. I'm so horrible at this part of Acid and base