(d) methyl red (e) phenolphthalein * Experiment P (Titration of a Weak Acid): A sample of acetic acid (initial concentration 0.500 M) was titrated using NaOH and a titration curve was prepared. An experimental value for pKa of 4.65 was obtained. Which of the following species (HA represents the acetic acid and A the acetate anion) has the larger concentration at pH 3.7; and at pH 5, respectively? (a) HA at pH-3.7; and A at pH-5* (d) H30+ at pH-3.7; and ATat pH-5 (e) A- at pH-3.7; and OH at pH-5 (b) HA at pH-3.7; and H30+ at pH-s ( (c) ATat pH-3.7; and HA at pH-5 Solution The chemical reaction can be written as HA + OH- <==> A- (aq) + H 2 O (l), we are adding base OH-, but we always calculate pH of the solution interms of H 3 O + . Since the acetic acid is in solution state 0.5 M, HA (aq), hence the actual pH calculation is based on H 3 O + only. Until acid dissociate and protonate water we cannot able to measure pH. We know lower the pH, more acidic the solution. Once we started adding base more A - will be formed and consequently pH increases (H 3 O + decreases). We also know that pH = pKa at half-equivalence point, the concentrations of HA = A - , at pH = 5 the concentartion of HA decreases and A - will increases. We are considering concentration of species NOT pH interms of H 3 O + , and also Henderson-Hasselbalch equation can be used here. pH = pKa + log [salt /acid] at pH = 3.7 ==> salt/acid = 0.11 ==> acid HA is more here due to small dissociation, but after capturing H + by H 2 O, there will be lesser H 3 O + . at pH = 5.0 ==> salt/acid = 2.24 ==> salt A- concentration is more Hence the correct option is (a) HA at pH = 3.7; and A - at pH = 5 Hope this helped you! Thank You So Much! Please Rate this answer as you wish.(\"Thumbs Up\") .

1. (d) methyl red (e) phenolphthalein * Experiment P (Titration of a Weak Acid): A sample of
acetic acid (initial concentration 0.500 M) was titrated using NaOH and a titration curve was
prepared. An experimental value for pKa of 4.65 was obtained. Which of the following species
(HA represents the acetic acid and A the acetate anion) has the larger concentration at pH 3.7;
and at pH 5, respectively? (a) HA at pH-3.7; and A at pH-5* (d) H30+ at pH-3.7; and ATat pH-5
(e) A- at pH-3.7; and OH at pH-5 (b) HA at pH-3.7; and H30+ at pH-s ( (c) ATat pH-3.7; and
HA at pH-5
Solution
The chemical reaction can be written as
HA + OH- <==> A- (aq) + H 2 O (l), we are adding base OH-, but we always calculate pH of the
solution interms of H 3 O +
. Since the acetic acid is in solution state 0.5 M, HA (aq), hence the
actual pH calculation is based on H 3 O +
only. Until acid dissociate and protonate water we
cannot able to measure pH.
We know lower the pH, more acidic the solution. Once we started adding base more A -
will be
formed and consequently pH increases (H 3 O +
decreases).
We also know that pH = pKa at half-equivalence point, the concentrations of HA = A -
, at pH =
5 the concentartion of HA decreases and A -
will increases.
We are considering concentration of species NOT pH interms of H 3 O +
, and also Henderson-
Hasselbalch equation can be used here.
pH = pKa + log [salt /acid]
at pH = 3.7 ==> salt/acid = 0.11 ==> acid HA is more here due to small dissociation, but after
capturing H +
by H 2 O, there will be lesser H 3 O +
.
at pH = 5.0 ==> salt/acid = 2.24 ==> salt A- concentration is more
Hence the correct option is (a) HA at pH = 3.7; and A - at pH = 5
Hope this helped you!

2. Thank You So Much! Please Rate this answer as you wish.("Thumbs Up")