# 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

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) and 1.00 mol dm-3 will be measured out using a 50.0 cm3 +/- 0.5 graduated cylinder, and poured into separate 150 cm3 clean, dry glass beakers. These two beakers will then be placed on the same electrically powered hotplate, which is set to medium-high heat. The temperatures will be monitored with separate Vernier temperature probes, connected to a Vernier LabQuest with LoggerPro  Data collection software. If one of the 150 cm3 beakers containing 40.0 cm3 of either 1.00 mol dm-3 KOH(aq) or 1.00 mol dm-3 HCl(aq) attains the desired temperature before another (since they may be starting at different temperatures), it will be temporarily set aside (off the hotplate) until the other one also attains this temperature and placed back if necessary to regain any heat lost from being set aside from the hotplate. Both beakers containing 40.0 cm3 of either 1.00 mol dm-3 KOH(aq) or 1.00 mol dm-3 HCl(aq) can therefore be placed on the hotplate until the necessary temperature is reached for both.

In the case where temperature will need to be reduced (likely only necessary for one of the variations: 19°C), an ice bath will be used. Specifically, 40.0 cm3 of room temperature 1.00 mol dm-3 HCl(aq) and 1.00 mol dm-3 KOH(aq) will be placed in separate, clean, and dry 150 cm3 glass beakers. An ice bath will be prepared ahead of time in a shallow, insulated tub with cold water and ice cubes placed inside. The two 150 cm3 beakers containing 40.0 cm3 of 1.00 mol dm-3 KOH(aq) and HCl(aq) separately, will then be placed in the ice bath at the same time until they reach the desired temperature of 19°C. If one of the solutions of KOH(aq) or HCl(aq) in the 150 cm3 beaker reaches the desired temperature of 19°C quicker, it can be briefly removed from the ice bath and re-introduced as necessary until the other solution catches up. Throughout the cooling process, the temperatures of both 40.0 cm3 samples of 1.00 mol dm-3 KOH(aq) and HCl(aq) solutions in the 150 cm3 beaker will be monitored using Vernier temperature probes, connected to a Vernier LabQuest with DataLogger Pro collection software so that they are reacted when both reach the same temperature.

[Note: A temperature of 19°C was selected as one of the lower variations because of the following reasons. One, it would be tedious and unfeasible to wait for the temperature of both solution of 1.00 mol dm-3 KOH(aq) and HCl(aq) to drop to lower degrees, such as 10°C. Also, if a lower temperature is selected, then it complicates to process of finding the maximum temperature measured during the reaction of the solution. For example, if 10°C was selected as a variation, and the temperature change caused by the neutralization reaction of 1.00 mol dm-3 KOH(aq) and HCl(aq) was actually an increase of 9°C, and the room temperature was 23°C, it would be difficult to accurately discern the maximum temperature from the data collected during this investigation since it would ‘peak’ at 23°C, or in other words, back to room temperature.]

Dependent Variable

The dependent variable in this investigation is the molar enthalpy change from the neutralization reaction, resulting from the reaction of two 40.0 cm3 solutions of 1.00 mol dm-3 HCl(aq) and KOH(aq) in a doubled polystyrene cup.

Since molar enthalpy is determined through a few different values that need to be collected during the investigation, the steps taken to determine the molar enthalpy of the reaction of 1.00 mol dm-3 HCl(aq) and KOH(aq) will be multiple.

Part of the calculations involved in determining the molar enthalpy change of a reaction is the mass of the reactants. In this investigation, the mass of the reactants will be determined from the volume of the 1.00 mol dm-3 KOH(aq) and HCl(aq) that is measured during the investigation. The volume will be read from two 50.0 cm3 +/- 0.5 graduated cylinders, which will each be assigned to measure either the 40.0 cm3 of 1.00 mol dm-3 HCl(aq) or KOH(aq) so as to also avoid cross-contamination. The mass of the solutions will then be determined through converting cm3 to grams, assuming that the density is that of pure ...