# Lab Report. Objective: To determine the concentration of unknown standard sodium hydroxide solution and the enthalpy change of neutralization between different pairs of acid-base used (Thermometric titration)

Laboratory Report: Experiment 4

Determination of the enthalpy change of neutralization

Name: Cheung Chun Hin, Harry        Class: 6L (12)                Date: 2-11-2009

Objective:

To determine the concentration of unknown standard sodium hydroxide solution and the enthalpy change of neutralization between different pairs of acid-base used (Thermometric titration)

Principle of method:

Neutralization is the reaction between an acid and a base, which is an exothermic reaction. In this experiment, two methods are used to determine the concentration of sodium hydroxide solution and the enthalpy change of neutralization.

H+(aq) + OH-(aq)  H2O(l)

Method 1 is to measure the temperature change of the reaction mixture when different definite ratio of acid and base are reacted. There are totally 7 ratios. For each ratio, the initial temperature of acid and base is recorded. When they are mixed, the final temperature of the mixture is recorded so that:

Let Va, Vb, Ta, Tb, T be the volume of acid, volume of base, initial temperature of acid, initial temperature of base and final temperature of mixture if they are not reacted (which is actually the initial temperature of mixture before reaction) respectively.

Thus, Final temperature of the mixture after reacted – T = Temperature change due to reaction

Method 2 is to measure the temperature of the reaction mixture when each small portion of acid are added to a fixed amount of base solution with using titration of acid against base.

For both of the method, different pairs of acid and base are used and compared.

To find the concentration of sodium hydroxide solution, the volume ratio of acid to base which makes the maximum temperature change(which means the reaction is most complete) should be found out and so:

(Since the basicity of both acid and base is 1)

By conservation of energy, the enthalpy change of neutralization = heat change of solution

The density and specific heat capacity of solution are assumed to be equal to those of water since the differences between them are negligible.

Results:

Method 1

Using nitric acid: (A graph is attached at page 6)

From the graph, the maximum temperature change in using nitric acid = 5.7

The corresponding volume ratio of acid to base = 20:20 = 1:1

Molarity of sodium hydroxide solution = 1÷1×1.00 = 1.00M

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