Part A A buffer is prepared by adding 22.0 g of sodium acetate (CHsCOONa) to 510
ID: 562330 • Letter: P
Question
Part A A buffer is prepared by adding 22.0 g of sodium acetate (CHsCOONa) to 510 mL of a 0 150 M acetic acid (CH,COOH) solution Determine the pH of the buffer Express your answer using two decimal plac pH M Answers Give Up Incorrect, Try Again Part B Write the complete ionic equation for the reaction that occurs when a few drops of hydrochloric acid are added to the buffer Express your answer as a chemical equation. Identify all of the phases in your answer SubmitM Answers Givwe le Part C Write the complete ionic equation for the reaction that occurs when a few drops of sodium hydroxide solution are added to the buffor press your answer as a chemical equation. Identify all of the phases in your answer.Explanation / Answer
A buffer is any type of substance that will resist pH change when H+ or OH- is added.
This is typically achieved with equilibrium equations. Both type of buffer will resist both type of additions.
When a weak acid and its conjugate base are added, they will form a buffer
The equations:
The Weak acid equilibrium:
HA(aq) <-> H+(aq) + A-(aq)
Weak acid = HA(aq)
Conjugate base = A-(aq)
Neutralization of H+ ions:
A-(aq) + H+(aq) <-> HA(aq); in this case, HA is formed, H+ is neutralized as well as A-, the conjugate
Neutralization of OH- ions:
HA(aq) + OH-(aq) <-> H2O(l) + A-(aq) ; in this case; A- is formed, OH- is neutralized as well as HA.
Now,
A)
pH = pKa + log(A-/HA)
pKa for acetic acid = 4.75
mol of A- = mass/MW = 22/82 = 0.2682
mol of acid = MV = 0.15*0.510 = 0.0765
pH = pKa + log(A-/HA)
pH = 4.75 + log(0.2682/0.0765) = 5.294
b)
for addition of HCl
HCl + CH3COO-(aq) --> CH3COOH + Cl-
net ionic
H+(aq) + CH3COO-(aq) --> CH3COOH(aq)
C)
for NaOH addition:
NaOH + CH3COOH(aq) --> CH3COO- + H2O
net ionic
OH-(aq) + CH3COOH(aq) --> CH3COO- + H2O
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