1. What is the pH of a solution that is 0.10 M HC2H3O2 and 0.20 M NaC2H3O2? Ka f
ID: 503851 • Letter: 1
Question
1. What is the pH of a solution that is 0.10 M HC2H3O2 and 0.20 M NaC2H3O2? Ka for acetic acid is 1.8x10-5.
2. Using Kb = 1.8x10-5 for NH3, or Ka = 1.8x10-5 for HC2H3O2 and 5.6x10^-11 for HCO3- calculate the Ka for NH4^+ and the Kb for the C2H3O2^- and CO3^2- ions.
3.Mass of NaC2H3O23H2O (FW = 82 g/mol) _________________________________
pH of the original buffer_____________________
pH of buffer + HCl_________________________
pH of buffer + NaOH_______________________
a. Calculate the pH of the original buffer based the amount of acid and conjugate base that you added
and the Ka. Do the calculated and measured values agree?
b. Comment on the pH changes when you added acid or base. Define a buffer and explain how a buffer
works.
Explanation / Answer
1)
pKa = -log Ka
= -log (1.8*10^-5)
= 4.745
CH3COOH and CH3COONa forms acidic buffer
pH = pKa + log {[CH3COONa]/[CH3COOH]}
= 4.745 + log (0.20/0.10)
= 4.745 + log (2)
= 5.05
Answer: 5.05
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