EXAMPLE PROBLEM APPLYING THE HENDERSON-HASSELBALCH EQUATION Calculate the pH of
ID: 538242 • Letter: E
Question
EXAMPLE PROBLEM APPLYING THE HENDERSON-HASSELBALCH EQUATION Calculate the pH of a buffer solution made from 0.20 M HC_2H_3O_2 and 0.50 M C_2H_3O_2^- that has an acid dissociation constant for HC_2H_3O_2 of 1.8 times 10^-5. Solve this problem by plugging the values into the Henderson-Hasselbalch equation for a weak acid and its conjugate base. pH = pK_a + log ([A^-]/[HA]) pH = pK_a + log ([C_2H_3O^-_2]/[HC_2H_3O_2]) pH = -log (1.8 times 10^-5) + log (0.50 M/0.20 M) pH = -log (1.8 times 10^-5) + log (2.5) pH = 4.7 + 0.40 pH =5.1Explanation / Answer
Ka = 1.8*10^-5
PKa = -log1.8*10^-5
= 4.74
PH = Pka + log[A-]/[HA]
HA is Acid = HC2H3O2 is aacid
A- is conjugate base = C2H3O2- is conjugate base
So [HA] = 0.2M
[A^-] = 0.5M
PH = Pka + log[A-]/[HA]
= 4.74 + log0.5/0.2
= 4.74 + 0.3979 = 5.1379
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