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# Enthalpy Change Design Lab (6/6)How does changing the initial temperature (19C, 25C, 35C, and 45C) of two 40.0 cm3 at 1.00 mol dm-3 solutions of KOH(aq) and HCl(aq) affect the molar enthalpy change of the neutralization reaction

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Introduction

Research Question: How does changing the initial temperature (19�C, 25�C, 35�C, and 45�C) of two 40.0 cm3 at 1.00 mol dm-3 solutions of KOH(aq) and HCl(aq) affect the molar enthalpy change of the neutralization reaction when the two are allowed to react in a doubled polystyrene cup? Hypothesis: If the temperature of both solutions of 1.00 mol dm-3 HCl(aq) and KOH(aq) is increased prior to the two reacting in a doubled polystyrene cup, then the molar enthalpy of the reaction between the two solutions should be greater since the reactants can fully react quicker since there is more energy in the surroundings of the KOH(aq) and HCl(aq) ions, so they will be moving faster, and will therefore result in a higher molar enthalpy change as compared to neutralization reactions of 1.00 mol dm-3 of KOH(aq) and HCl(aq) occurring at lower initial temperatures at the time of reaction. Independent Variable The independent variable in this investigation is the temperature at which both the 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq) are at, at the time of the neutralization reaction between the two is being performed in a doubled polystyrene cup. The variations of temperature of the 1.00 mol dm-3 KOH(aq) and 1.00 mol dm-3 HCl(aq) that will be used in the investigation are 19�C, 25�C, 35�C, and 45�. This offers a suitable, wide spectrum of temperatures at which the reactants will be combined to neutralize, and should prompt a noticeable trend in the molar enthalpy of the reaction between 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq). This variable will be manipulated through the use of both hot plates and ice baths. Specifically, the temperature of both 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq) will be measured at the start of the investigation (and will likely be around room temperature, so 3/4 variations in temperature will require heating steps to be taken). Then, to achieve higher temperatures for the reactants, 40.0 cm3 of both the 1.00 mol dm-3 HCl(aq) ...read more.

Middle

This would therefore render it the limiting reactant in the reaction between it and 1.00 mol dm-3 HCl(aq), and would affect the molar enthalpy change by releasing/gaining less heat from the surroundings than it should ideally. This variable will be controlled by preparing the 1.00 mol dm-3 KOH(aq) solution as close to the time of the investigation as possible. Specifically, it is recommended that the solution be prepared the morning of the investigation, and the investigation carried out later that day. In addition, the flask containing the 1.00 mol dm-3 KOH(aq) solution should be firmly sealed with a rubber stopper to prevent fresh, moist air entering and further diluting the solution due to the hygroscopic nature of KOH(aq). 5. Heat loss and the time it takes for the reactants to fully react is a variable that must be controlled, or worked towards ensuring is consistent. In terms of heat loss, it is important to prevent the loss of heat from the neutralization reaction because it means that heat is escaping the calorimeter, and not contributing towards raising the temperature of the resulting solution from the neutralization reaction between 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq). A proper analogy is cooking stew on the stove - one wants to insulate the heat inside the pot so that the safe temperature for cooking meat is achieved. The same case exists in the simple calorimeter, in that to achieve as accurate a molar enthalpy change as possible for a trial, it is important to limit the amount of heat lost to the surroundings around the calorimeter so that the most accurate molar enthalpy change for the reaction of 40.0 cm3 of both 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq). On the topic of rate of reaction, it is helpful if both reactants react as 'instantly' as possible. This is because the longer it takes for the neutralization reaction of 1.00 mol dm-3 KOH(aq) ...read more.

Conclusion

or KOH(aq) that was removed earlier rose to above the 19.0 �C target, it was temporarily replaced into the ice bath to regain the appropriate temperature. The two solutions of 1.00 mol dm-3 HCl(aq) and KOH(aq) were alternated in their respective 150 cm3 beaker in and out of the ice bath until both Vernier LabQuest's read that the temperature of both solutions was 19.0 �C. 10. Once both Vernier LabQuest's indicated that the 40.0 cm3 of 1.00 mol dm-3 HCl(aq) and 40.0 cm3 of 1.00 mol dm-3 KOH(aq) were at the 19.0 �C target temperature, the contents of the 150 cm3 beaker labelled 'HCl(aq)' were poured into the clean doubled polystyrene cup, containing the magnetic stirring bar that was already spinning, with the electrically powered stirrer set at a speed of medium. 11. The temperature probe that was being used to monitor the temperature of the 40.0 cm3 solution of 1.00 mol dm-3 HCl(aq) while in the 150 cm3 beaker, was then placed in the doubled polystyrene cup to attain the more accurate initial temperature, and the base of the probe was pressed against the base of the polystyrene cup so as to ensure it was deep enough into the solution. The temperature was recorded. 12. As quickly and safely as possible, the contents of the 150 cm3 beaker labelled 'KOH(aq)' (40.0 cm3 of 1.00 mol dm-3 KOH(aq)) were then emptied into the doubled polystyrene cup, containing 40.0 cm3 of 1.00 mol dm-3 HCl(aq) and the temperature probe that is connected to the Vernier LabQuest LoggerPro data collector. The Vernier LabQuest LoggerPro was then monitored, until a steady decrease from the peak temperature was observed. The interface was then consulted to determine the maximum temperature measured during the neutralization reaction. 13. The contents of the doubled polystyrene cup were safely disposed of in an appropriate waste container, and the magnetic stirring bar was also retrieved. 14. Steps 3-14 were repeated for a further 2 trials, using the same equipment (except the doubled polystyrene cup and the two 150 cm3 beakers were washed, cleaned, and dried). ...read more.

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