Enthalpy of Neutralisation Between HCl and NaOH

 = ± 0.1)        

                                                                (

 = (± 0.1/6.2 °C)

 100 = ±1.61%)

Therefore, the average change in temperature for this experiment is calculated to be ΔT= 6.2°C

Using the equation

, we can ascertain the amount of energy, in joules, lost by the NaOH and HCl solutions when they neutralized to form H2O and NaCl:

For m we are using the value of 40 grams for 20cm3 of HCl and 20cm3 of NaOH, and C is a constant at ~4.18Jcm-3°C-1 (3 s.f). Therefore,

                                                ( %m = (1/40)

 100 =±2.5% )        

Joules                                                (

 + %m = ± 4.11)        

                                                                (%

 100  = ± 0.396%)

n(HCl) =

        

 1.00mol dm -3

0.020mol dm-3

        

 moles                                        (%n =± 2.5%)

n(NaOH) =

        

 1.00mol dm -3

0.020mol dm-3

        

 moles                                        (%n = ±2.5%)

                                                        (

 = %n + %q)

                                                (

 = ± 2.89)

                                                (%

 100  = ±5.56%)

Conclusion:

The literature value for ΔH in the neutralization of NaOH and HCl is ΔH=-57.1 kJmol-1

The precision error, or random error attributed to the precision of instruments is ±5.56%, which is highish for a precision error. However, the literature value for the neutralization of NaOH with HCl to form H2O and NaCl is still outside the possible range that we obtained through this experiment, including the precision error.

Therefore, there must also be some experimental error present also. This experimental error can be determined as a percentage through the following formula:

In this case, this is written as:

This experimental error is also very large, but in a similar order of magnitude as the systematic error, which was very large for a systematic error. Therefore, it is difficult to determine with certainty where most of the error came from (either from systematic error or experimental error), but considering the range of likely reasons for experimental error to be present, it is more likely that experimental error, not systematic error, is most to blame for the  deviation from the literature value.

Evaluation:

The large random error in this experiment was die the large number of operations needed to determine the ΔH value in this experiment therefore an increased level of accuracy in the equipment would have increased our ability to determine a more accurate result. Increasing accuracy in equipment would have aided the experiment although the literature value was still outside the range of random error.

While it is unsure how large the experimental error was in comparison to random error, there are several possible factors for the large experimental error. The first and most prominent of these reasons is the likelihood of energy being lost from the system to the surroundings. While conducting the experiment, I noticed that the polystyrene cup warmed up slightly, which suggests that heat energy, released as a result of this experiment was dissipating into the surroundings: the polystyrene cup, the temperature probe itself, and the air. This would have lowered the value of ΔT and therefore lowered the value of ΔH. This experiment could be improved, therefore, if the experiment was carried out in a more insulated container, which would allow heat to escape at a much slower pace than the container we used. An airtight lid would also not allow heat to be lost to air, which may have played a big part in the loss of heat energy to surroundings.

Another reason for loss of heat to the surroundings would be that small air bubbles were formed from stirring. This means that our stirring which increased the number of collisions of  the dissolved particles in the solution with other dissolved particles, was also causing particles of water to collide more frequently with particles of air. This means that as there was a large number of collisions happening between the solution and the air, then it is more likely that heat energy from the solution was imparted and ‘lost’ to the air. This would decrease the value of ΔT, and in turn, ΔH, giving us a lower value of ΔH than the experimental value. An improvement to this could be to find a new way of mixing together the two solutions effectively, such as for them to be shaken in an airtight container, or stirred more smoothly.

As the two reactant solutions were clear and that the product solution with a salt dissolved in it was also clear, then it is impossible to tell using the naked eye whether all of the NaOH or HCl had undergone the neutralization process, as no colour change would indicate that it had. Therefore, it is possible that not all of the NaOH and HCl had reacted with one another, and therefore had not released the heat energy we were expected to read. This would give us a lower value of ΔT than we should have received, which in turn would give us a value of ΔH that is lower than the literature value. This is difficult to improve upon, as adding indicator solution may contaminate the experiment. However, adding a pH indicator could show if there were areas in the container which was slightly acidic (and therefore high in unreacted HCl) or slightly alkaline (and therefore high in unreacted NaOH). A pH probe may also be used to tell us the same thing.