Acid-Base Titration Curves Using a pH Meter
Introduction:
In this experiment you will use a pH sensor to collect volume and pH data as you titrate two acids with
sodium hydroxide.
You will obtain titration curves for the following combinations of acids and bases (exact concentrations
will be labeled on the reagent bottles and should be written in your data table):
1) hydrochloric acid, HCl(aq) with sodium hydroxide, NaOH(aq);
2) acetic acid, CH3COOH(aq) with sodium hydroxide, NaOH(aq).
The recorded volume and pH values will generate titration curves that will be used to compare features
of the strong acid curve versus the weak acid curve. You will determine the equivalence point volume
and pH for both curves. You will estimate the pKa and the Ka for a weak acid from its titration graph.
Refer to Sections 14.2, 14.3, and 14.7 of Openstax Chemistry for information on pH calculations,
relative strengths of acids and bases, and acid-base titrations.
Equations to use for the calculations and Explanations:
In an acid-base neutralization reaction, an acid reacts with a base to produce a salt and water:
HA(aq) + MOH(aq) MA(aq) + H2O(l) Equation 1
Acid Base Salt
At the equivalence point for an acid-base neutralization reaction, the amount of base added is equal to
the amount of acid initially present; thus, the acid has been completely neutralized.
When a weak acid solution is initially present, the following ionization reaction will occur:
HA(aq) H+(aq) + A-(aq) Equation 2
[H ][ A ]
The equilibrium constant for the ionization of the weak acid, Ka, is: Ka = Equation 3
[HA ]
At the volume half-way to the equivalence point during the titration of a weak acid by a strong base,
one-half of the weak acid, HA, has been converted to its conjugate base, A -. Thus, at this half-
equivalence point, [HA] = [A-], and Equation 3 simplifies to: Ka = [H+].
By taking the negative log of both sides, this expression becomes:
pKa = pH at the the half-equivalence point Equation 4
The equivalence point occurs at the midpoint of the region where the pH rises rapidly. The pKa can be
determined by estimating the pH at the volume halfway to the equivalence point. Figure 1b on page 2
shows the location of the equivalence point and half-equivalence point on a weak acid curve. The Ka for
a weak acid can then be found from Equation 5:
Ka = 10-pKa Equation 5
Finally, the absolute % difference can be calculated for the weak acid ionization constant:
Absolute % difference = |experimental Ka−theoretical Ka
| 𝑥100% Equation 6
theoretical Ka
GCC CHM 152LL: Acid-Base Titration Curves © GCC 2019 page 1 of 8
, Analyzing Titration Curves:
Figure 1a. Distribution of drops to yield a Figure 1b. Acid-Base Titration curve for WEAK
Titration with smooth curves. monoprotic acid.
Materials:
2 – 150 mL beakers GoLink
25 mL buret magnetic stir bar
buret clamp KimWipes
Hot/Stir plate pH calibration solutions (pH 4 and pH 7)
250 mL beaker ~ 0.1 M NaOH (record exact concentrations for
10.00 mL volumetric pipet all solutions)
pipet pump ~ 0.1 M HCl
3-finger clamp ~ 0.1 M CH3COOH
pH probe ruler
Chromebook
Procedure: This lab will be performed in two weeks. You will collect data for the HCl-NaOH
titration the first week. You will collect data for the CH 3COOH-NaOH titration and work on
post-lab calculations the second week.
***Caution: Sodium hydroxide will attack your skin and is very effective at destroying the
tissue of the eyeballs. Make sure you are wearing your goggles at all times and that you rinse
off any sodium hydroxide immediately!***
1. Obtain about 15 mL of hydrochloric acid and 50 mL of NaOH in separate beakers.
2. Calculate the volume of base needed for your titration and show your professor the answer. Note:
you should assume that 10.00 mL of acid is present for the titration since that is the amount you
pipet into the titration beaker.
3. Clean and condition the buret with base – refer to the “Using a buret to deliver solution”
technique. You should also review the “Performing a Titration” technique. After conditioning, fill
the buret with NaOH and adjust the level of NaOH so that is initially at (or very close to) 0.00 mL.
4. Add 50 mL of deionized water into a 250 mL beaker. Pipet 10.00 mL of HCl into the beaker.
5. Assemble the Chromebook, GoLink, and pH probe system – refer to the “Using and calibrating a
pH probe” technique. Calibrate the pH probe using the pH 4 and pH 7 buffer solutions. Allow
some space between your titration equipment and the computer!
GCC CHM 152LL: Acid-Base Titration Curves © GCC 2019 page 2 of 8
Introduction:
In this experiment you will use a pH sensor to collect volume and pH data as you titrate two acids with
sodium hydroxide.
You will obtain titration curves for the following combinations of acids and bases (exact concentrations
will be labeled on the reagent bottles and should be written in your data table):
1) hydrochloric acid, HCl(aq) with sodium hydroxide, NaOH(aq);
2) acetic acid, CH3COOH(aq) with sodium hydroxide, NaOH(aq).
The recorded volume and pH values will generate titration curves that will be used to compare features
of the strong acid curve versus the weak acid curve. You will determine the equivalence point volume
and pH for both curves. You will estimate the pKa and the Ka for a weak acid from its titration graph.
Refer to Sections 14.2, 14.3, and 14.7 of Openstax Chemistry for information on pH calculations,
relative strengths of acids and bases, and acid-base titrations.
Equations to use for the calculations and Explanations:
In an acid-base neutralization reaction, an acid reacts with a base to produce a salt and water:
HA(aq) + MOH(aq) MA(aq) + H2O(l) Equation 1
Acid Base Salt
At the equivalence point for an acid-base neutralization reaction, the amount of base added is equal to
the amount of acid initially present; thus, the acid has been completely neutralized.
When a weak acid solution is initially present, the following ionization reaction will occur:
HA(aq) H+(aq) + A-(aq) Equation 2
[H ][ A ]
The equilibrium constant for the ionization of the weak acid, Ka, is: Ka = Equation 3
[HA ]
At the volume half-way to the equivalence point during the titration of a weak acid by a strong base,
one-half of the weak acid, HA, has been converted to its conjugate base, A -. Thus, at this half-
equivalence point, [HA] = [A-], and Equation 3 simplifies to: Ka = [H+].
By taking the negative log of both sides, this expression becomes:
pKa = pH at the the half-equivalence point Equation 4
The equivalence point occurs at the midpoint of the region where the pH rises rapidly. The pKa can be
determined by estimating the pH at the volume halfway to the equivalence point. Figure 1b on page 2
shows the location of the equivalence point and half-equivalence point on a weak acid curve. The Ka for
a weak acid can then be found from Equation 5:
Ka = 10-pKa Equation 5
Finally, the absolute % difference can be calculated for the weak acid ionization constant:
Absolute % difference = |experimental Ka−theoretical Ka
| 𝑥100% Equation 6
theoretical Ka
GCC CHM 152LL: Acid-Base Titration Curves © GCC 2019 page 1 of 8
, Analyzing Titration Curves:
Figure 1a. Distribution of drops to yield a Figure 1b. Acid-Base Titration curve for WEAK
Titration with smooth curves. monoprotic acid.
Materials:
2 – 150 mL beakers GoLink
25 mL buret magnetic stir bar
buret clamp KimWipes
Hot/Stir plate pH calibration solutions (pH 4 and pH 7)
250 mL beaker ~ 0.1 M NaOH (record exact concentrations for
10.00 mL volumetric pipet all solutions)
pipet pump ~ 0.1 M HCl
3-finger clamp ~ 0.1 M CH3COOH
pH probe ruler
Chromebook
Procedure: This lab will be performed in two weeks. You will collect data for the HCl-NaOH
titration the first week. You will collect data for the CH 3COOH-NaOH titration and work on
post-lab calculations the second week.
***Caution: Sodium hydroxide will attack your skin and is very effective at destroying the
tissue of the eyeballs. Make sure you are wearing your goggles at all times and that you rinse
off any sodium hydroxide immediately!***
1. Obtain about 15 mL of hydrochloric acid and 50 mL of NaOH in separate beakers.
2. Calculate the volume of base needed for your titration and show your professor the answer. Note:
you should assume that 10.00 mL of acid is present for the titration since that is the amount you
pipet into the titration beaker.
3. Clean and condition the buret with base – refer to the “Using a buret to deliver solution”
technique. You should also review the “Performing a Titration” technique. After conditioning, fill
the buret with NaOH and adjust the level of NaOH so that is initially at (or very close to) 0.00 mL.
4. Add 50 mL of deionized water into a 250 mL beaker. Pipet 10.00 mL of HCl into the beaker.
5. Assemble the Chromebook, GoLink, and pH probe system – refer to the “Using and calibrating a
pH probe” technique. Calibrate the pH probe using the pH 4 and pH 7 buffer solutions. Allow
some space between your titration equipment and the computer!
GCC CHM 152LL: Acid-Base Titration Curves © GCC 2019 page 2 of 8
