Posted by Jessie on Sunday, April 25, 2010 at 12:24pm.
a) Use the Henderson-Hasselbalch equation shown on the next line below.
b) pH = pKa + log[(base)/(acid)]
When the solution is diluted you change the base concn and you change the acid concn but does the ratio change?
c) Addition of HCl increases concn acid and decreases formate (base).
d) Addition of NaOH, decreases formic acid and increases formate (base).
Post your work if you get stuck.
i understand a and b, but how do i calculate parts c and d?
c) The way a buffer works:
1. If strong acid is added (HCl for example), the base (HCOO^-) takes over and ties up the H^+ by forming HCOOH. So the HCOOH concn is increased and the HCOO^- is decreased by the same amount, the log base/acid term changes and pH changes slightly but not too much because instead of adding a strong acid the system thinks we just added a little more of the weak formic acid.
How much HCOO^- (formate) did we have?
We had 100 mL x 0.6 M = 60 mmoles formate.
We had 100 mL x 0.4 M = 40 mmoles HCOOH.
(You don't need to convert to moles, you CAN still use molarities).
So we add 5 mL x 1 M HCl = 5 mmoles HCl.
That means the new mmoles HCOOH is 40+5 = 45. The new mmoles formate (HCOO^-) is 60-5= 55.
Plug those values into the HH equation and solve for pH.
2. When NaOH is added to a formic acid/formate buffer, it works this way.
The NaOH is neutralized by the formic acid to form more sodium formate. So the acid is decreased, the formate is increased. This is done the same way as part c.
thank you!
Related Questions
Chemistry - How many grams of formic acid, HCOOH, must be added to 0.270L of 0....
chem ll - How many grams of formic acid, HCOOH, must be added to 0.270L of 0....
chemistry - What is th pH of a buffer solution made by dissolving 0.10 mol of ...
college - 0.10 moles HCOOH (formic acid) and 0.02 moles HCOONa (sodium formate) ...
Chemistry - A buffer is prepared by mixing 0.30 mole of formic acid (HCNO2) and ...
chemistry - A. Strong Base 1.) What is the concentration of a solution of KOH ...
Chem II - Find the mass of sodium formate that must be dissolved in 200.00cm^3 ...
chemistry - How many grams of potassium formate, KHCOO, must be added to 500 mL ...
CHEM - For the reaction shown, find the limiting reactant for each of the ...
Chemistry help needed - How do I prepare 90% formic acid from conc. formic acid...
For Further Reading
