Ibdp Chemistry Ia Enthalpy Change of Neutralisation

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Aim:

To calculate the enthalpy change of neutralization of the given pairs of acid and base.

Theory:

When alkali neutralizes an acid, a salt and water are formed. Aqueous hydrogen ions, H+(aq) from the acid react with the hydroxide ions, OH-(aq) from the alkali, forming water.

Ionic equation: H+ (aq)+OH- (aq) → H2O (l)

The identity of the salt will depend on the nature of the acid and alkali used.

The combination of H+ and OH- ions in this way releases energy. In this practical, the enthalpy changes accompanying different neutralization reactions will be measured. It is because the number of moles of water formed varies according to the acid and alkali used, it is the convention to measure enthalpy change of neutralization in kJ mol-1 when 1 mole of water is formed.

We will use a simple calorimeter to determine the enthalpy change of neutralization for the pairs of acid and base given.

Apparatus and Materials:

1.0mol dm-3 sodium hydroxide solution, 1.0 mol dm-3 hydrochloric acid, 1.0 mol dm-3 ethanoic acid, polystyrene cup with lid, thermometer, two 50.00cm3 measuring cylinders, stopwatch, three 80cm3 beakers, dropper

Variables:

Manipulated variable: Type of acids used
In this experiment, type of acids used would be manipulating variable. Different acids such as HCl or CH3COOH are added to NaOH respectively and measure the increase in temperature respectively.

Responding variable: Temperature, T
Responding variable will be the temperature. First, we have to measure and record the initial temperature of the sodium hydroxide solution. After acid has been added, record the temperature of the solution at different time.

Controlled variable: Concentration of sodium hydroxide
In this experiment, variables that have to be kept constant will be the factors that will affect the exothermic neutralization reaction. Thus, concentration of sodium hydroxide has to be kept constant. This is to make sure the number of moles of hydroxide ions OH- reacts with H+ remains constant, so as to determine the concentration of the acids.

Diagram:

Thermometer
Thermometer
Cover
Cover

Polystyrene cup
Polystyrene cup

25.0 cm3 HCl
25.0 cm3 HCl

Diagram 1: Set-up of the apparatus
Diagram 1: Set-up of the apparatus

Safety and Precaution Steps:

1. Always wear an apron and goggles in the lab.
2. Acids are corrosive; make sure that gloves are worn throughout the experiment.

Procedure:

1. Measure 25.0 cm3 of the hydrochloric acid using a 50.0 cm3 measuring cylinder into a polystyrene cup. Record its temperature for 3 minutes at 1 minute intervals. This is the initial temperature. 2. Put 25.0 cm3 of sodium hydroxide solution in a 50.0cm3 measuring cylinder. (Ensure that the temperature of the sodium hydroxide solution is the same as the acid). Now pour this into the acid, stir and take the temperature. 3. Record the temperature of the solution at every 1 minute interval, until there is at least 2oC temperature change after the maximum temperature has been attained. 4. Tabulate the results appropriately.

5. Repeat the experiment (steps 1−4) with ethanoic acid.

Results:

Raw Data:
Table 1: Table shows thermometer readings
t/ min±0.002 min| HCl is used| Ethanoic acid is used|
| T/ oC±0.5oC| T/ oC±0.5oC|
0.000| 29.0| 28.0|
1.000| 29.0| 28.0|
2.000| 29.0| 28.0|
3.000| 29.0| 28.0|
4.000| 36.0| 34.5|
5.000| 35.5| 34.0|
6.000| 35.0| 33.5|
7.000| 34.5| 33.5|
8.000| 34.5| 33.0|
9.000| 34.0| 33.0|
10.000| 33.5| 32.5|

Concentration of NaOH used = 1.00 mol dm-3
Volume of NaOH used = 25.0±0.5 mol dm-3
Concentration of HCl = 2.0 mol dm-3
Volume of HCl used = 25.0±0.5 mol dm-3
Concentration of CH3COOH = 2.0 mol dm-3
Volume of CH3COOH used = 25.0±0.5 mol dm-3

Observation:
1. The solution remains colorless before and after the reaction. 2. The polystyrene cup becomes warmer when acid is...
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