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Find the solubility of potassium nitrate in water at different temperatures and to estimate the solubility of potassium nitrate at 50ºC, and estimate the approximate value for the enthalpy of solution of potassium nitrate in water.

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Introduction

Introduction Aim My aim is to find the solubility of potassium nitrate in water at different temperatures and to estimate the solubility of potassium nitrate at 50�C, and estimate the approximate value for the enthalpy of solution of potassium nitrate in water. Background Knowledge Enthalpy is the amount of energy possessed by a thermodynamic system for transfer between itself and its environment. For example, in a chemical reaction, the change in enthalpy of the system is the heat of the reaction. In a phase change, as from a liquid to a gas, the change in enthalpy of the system is the latent heat of vaporization. In a simple temperature change, the change in enthalpy with each degree is the heat capacity of the system at constant pressure. The German physicist Rudolf J.E. Clausius originated the term in 1850. Mathematically, enthalpy H is identified as U + PV, where U is internal energy, P is pressure, and V is volume. ...read more.

Middle

Then using a burette I will add 8.0 cm� of distilled water. After that I will place a thermometer into the boiling tube and leave it there for the rest of the experiment. I will then heat the mixture carefully using a Bunsen burner. I will make sure that I hold the boiling tube at a 45� angle above the Bunsen burner and keep it at a level distant. I will then allow the mixture to cool in the air whilst stirring it with the thermometer. In addition to speed up the cooling process I will immerse the mixture in a beaker of cold water for a short amount of time. I will still continue to stir the mixture and then place a piece of black card behind the tube so I can clearly see when the crystals appear. Once the crystals appear I will note the temperature to the nearest 0.5�C. ...read more.

Conclusion

When I analysed my Log 10 ? Against 1/T graph I discovered that the enthalpy value for the solution of potassium nitrate in water was 19113KJ mol. Evaluation When I carried out this experiment I believe I did it in a careful and accurate way because I stuck to the instructions given. I could have improved my experiment in many ways. I, who could not have known the exact level of water in the burette, made the reading of water from the burette. So if I had used more precise equipment I could have had more accurate results. An improvement I could have made in this experiment was to first have done a preliminary study to find any mistakes I made and find a way to over come them. Another way of improvement could have been repeating the experiment 4 more times so that I had 5 sets of results and could have used the average results to work from. This would have pointed out any anomalous results and any mistakes I could have made in one of the experiments. ...read more.

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