Name Show All Work!! Exam 3 Take Home 40 pts) N. Lippolis Propionic acid is a we
ID: 509657 • Letter: N
Question
Name Show All Work!! Exam 3 Take Home 40 pts) N. Lippolis Propionic acid is a weak organic acid. A 0.123 M propionic solution is titrated by a 0.123 M sodium hydroxide solution. The initial volume of the propionic solution is 65.0 mL The K. of propionic acid is 1.34 x 10 A. Write the overall reaction with the correct states for the reaction between propionic solution and sodium hydroxide. B. Write the net ionic reaction for part A (include states) C. Calculate the pH before any sodium hydroxide has been added (initial solution) D. Calculate the pH after 20.0 mL of sodium hydroxide has been added.Explanation / Answer
Question 1.
A)
overall reaction for:
Propionic Acid + NaOH = NaPropionat + H2O
CH3CH2COOH + NaOH = NaCH3CH2COO + H2O
b)
net ionic reaciton must include all those species reacting
CH3CH2COOH(aq) + Na+(aq) + OH-(aq) --> Na+(aq) CH3CH2COO(aq) + H2O(l)
Note that only NA+ is spectator ions so
CH3CH2COOH(aq) + OH-(aq) --> CH3CH2COO(aq) + H2O(l)
c)
pH before anything is added
Ka = [H+][A-]/[HA ]
1.35*10^-5 = x*x/(0.123-x)
x = H = 0.00128
pH= -log(0.00128) = 2.89279003
d)
pH after
V = 20 mL of base is added
mmol of acid = MV = 0.123*65 = 7.995
mmol of base = MV = 0.123*20 = 2.46
pKa = -log(Ka) = -log(1.34*10^-5) = 4.8728
apply buffer equation
pH = pKa + log(A-/HA)
pH = 4.8728 + log(2.46/7.995) = 4.3609166
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