F.6/7 Chemistry Practical: Enthalpy of Neutralization
Objective:
To determine standard molar enthalpy of neutralization of sulphuric(VI) acid and sodium hydroxide
Group size: Two students
Preparation
Students should have two pieces of graph paper, erasing rubber and pencil for immediate drawing of
the graph and checking after the completion of the practical.
Introduction
In this practical, enthalpies of neutralization of the following reaction are measured:
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
by using different pairs of acid and alkali. For example, 2 M H2SO4 and 4 M NaOH, 1 M H2SO4 and 2
M NaOH, 0.5 M H2SO4 and 1 M NaOH, 0.2 M H2SO4 and 0.4 M NaOH, etc. Molar enthalpy of
neutralization for theses reaction pairs can be calculated and standard molar enthalpy of neutralization
between sulphuric(VI) acid and sodium hydroxide can be determined.
Ideas for writing your Theory Section
1. Define the term “standard molar enthalpy of neutralization”.
2. Show the method that you calculate heat change from the temperature change of the reaction
mixture in this experiment.
3. Show, how do you determine molar enthalpy of neutralization from the heat change of the reaction
mixture.
4. Show, how do you determine the value of standard molar enthalpy of neutralization from the
values of molar enthalpy of neutralization.
Technician’s note
Try to prepare the acids and alkalis early so that temperature of these solutions are the same as the
temperature of the surroundings.
Chemicals (For one group)
40 cm3 of Sulphuric(VI) acid of concentrations: 2M, 1M, 0.5M, 0.2M (in four burette set on side bench
for the whole class), 30 cm3 of sodium hydroxide of concentrations: 4M, 2M, 1M, 0.4M
Aparatus/Materials
Foam cup of capacity 100 cm3, thermometer, readable 0.2oC, 25 cm3 pipette
Procedure
1. From a burette run 25.0 cm3 of sulphuric(VI) acid into a polystyrene cup. Measure the temperature
of the acid. Compare this temperature and the temperature of the laboratory.
2. Pipette 25.0 cm3 of 4 M sodium hydroxide solution into the cup. Stir the mixture by using the
thermometer. Read the temperature of the mixture in a constant interval, starting from the time of
mixing (e.g. 5 seconds).
3. Repeat step 1 to 2, but concentrations of the acid and alkali are varied, according to the table given
in Data and Results section.
Results and Calculation
Enter your data in the following table and calculate molar enthalpy change for each reaction pair.
Final
Acid/alkali pair
Initial
o
Temperature Enthalpy change of the
o
temperature( C) temperature( C)
2 M H2SO4 and 4
M NaOH
1 M H2SO4 and 2
M NaOH
0.5 M H2SO4 and
o
rise( C)
mixture (J)
Molar enthalpy change
(kJ mol-1)
1 M NaOH
0.2 M H2SO4 and
0.4 M NaOH
Analysis of Results
Plot concentration of sulphuric(VI) acid against molar enthalpy change. From your graph, estimate the
value of the standard molar enthalpy change
Error Analysis
List major error sources in this practical and suggest methods to minimize the errors.
What is the major systematic error in this experiment?
Guidelines for discussion
1. Value of standard molar enthalpy change for this particular reaction is obtained by drawing a
straight to meet the ordinate (the axis of enthalpy change). Why is it done in this way?
2. Is your value of standard molar enthalpy change applicable to the neutralization reaction between
(a) hydrochloric acid and potassium hydroxide and (b) ethanoic acid and ammonia? Explain your
answers.
Hand in your practical report to Mr. Lai before 4:30 p.m.