The acetic acid is a weak acid as it does not completely dissociate in dilute aqueous solutions into hydrogen (H+) and acetate (CH3COO-) ions. When acetic acid is neutralized with a strong base (NaOH), heat is evolved during the neutralization that is used in the process of dissociating the acetic acid further that will facilitate the completion of neutralization. CH3COOH + NaOH = CH3COONa + H2O + heat The enthalpy change associated with the neutralization of acetic acid with a strong base is lower than that of the enthalpy of neutralization of a strong acid with a strong base. The difference in the enthalpy of neutralization of a strong acid (HCI) with a strong base (NaOH) and enthalpy of neutralization of weak acid (CH3COOH) with a strong base (NaOH) is the enthalpy of ionization of the weak acid (CH3COOH).

1. SHREE MALLIKARJUN COLLEGE CLASS:FYBSC
SAFETY: Refer to the MSDS acetic acid and sodium hydroxide.
-Dr. Mithil S. FalDesai
Aim: Determination of enthalpy of ionization of acetic acid.
Chemicals: Acetic acid, sodium hydroxide
Apparatus/Instrument: Beaker, measuring cylinder, thermometer, calorimeter
Theory: The acetic acid is a weak acid as it does not completely dissociate in dilute aqueous
solutions into hydrogen (H+) and acetate (CH3COO-) ions. When acetic acid is neutralized with a
strong base (NaOH), heat is evolved during the neutralization that is used in the process of
dissociating the acetic acid further that will facilitate the completion of neutralization.
CH3COOH + NaOH  CH3COONa + H2O + heat
The enthalpy change associated with the neutralization of acetic acid with a strong base is lower
than that of the enthalpy of neutralization of a strong acid with a strong base. The difference in
the enthalpy of neutralization of a strong acid (HCI) with a strong base (NaOH) and enthalpy of
neutralization of weak acid (CH3COOH) with a strong base (NaOH) is the enthalpy of ionization
of the weak acid (CH3COOH).
ΔHionization = ΔHneutralization (HCl-NaOH) - ΔH neutralization (CH3COOH-NaOH) ---------eq 1
Above reaction is done in a calorimeter whose heat capacity (Ccal) is previously determined or
known. The heat change during the neutralization is measured using a thermometer. Change in
temperature after mixing acetic acid and NaOH is given by
Δt = T2-T1 ---------eq 2
Thus, heat gained by the calorimeter is equal to the heat of neutralization (qneutralization).
qneutralization = Ccal XΔt ---------eq 3
The enthalpy of neutralization (ΔHneutralisation) is given by
ΔHneutralisation = (qneutralization)/Number of moles of water formed ---------eq 4
The unit of enthalpy is J mol-1.
Procedure:
1) Take 50 ml of 2.0 M CH3COOH and 50 mL of 2.0 M NaOH in two beakers; wait for 30 min
so that both the solutions attain the room temperature.
2) Measure the temperature of both the solutions so that they are equal (T1).
3) Pour 50 ml of 2.0 M CH3COOH in the calorimeter.
4) Add quickly 50 ml of 2.0 M NaOH and stir.
5) Note down the maximum temperature of the resultant solution attained after the mixing (T2).
6) Repeat the experiment for a set of readings.
Result: 1) The enthalpy of neutralization of acetic acid with sodium hydroxide =___ J mol-1.
2) The enthalpy of ionization of acetic acid =___ J mol-1.