By: Howard Andres

In this laboratory experiment, our lab group’s purpose was to use a coffee cup calorimeter to determine the heat flow involved when a substance is put into the calorimeter.  This experiment involved three different tests of heat flow, one with heated little beads of metal put into the calorimeter, another with an unknown white, crystalline-looking solid placed into the calorimeter, and another with measuring the heat of neutralization when HCl and NaOH are reacted in the calorimeter.  Using the measurements obtained with a scale and thermometer, our lab group was able to determine various calculations, such as the  t of the water and metal, and the specific heat and molar mass of the metal in Part A., the  H for the reaction and solution in Part B., and the  H of neutralization in Part C., just to name a few.  The q of the H₂0 was found in all three parts.

In Part A. of the experiment, our lab group placed the little beads of metal into a stoppered test tube and put it into a beaker of water until the water finally reached boiling under a hot plate.  By subtracting the final equilibrium temperature of the water with its initial temperature, the  t was found to be 5.5⁰C.  The  t of the metal was found using the same method, which came out to be -72.5⁰C.  Along with the specific heat of water and its determined mass, the q of the H₂0 was found to be 908 J.  Then, by using this answer with the mass and  t of the metal, its specific heat was found to be .278 J/g⁰C.  Through using the obtained specific heat in an equation, the molar mass of the metal was found to be 89.8g/mol.

In Part B. of the experiment, a similar procedure was used as in Part A., but the solid was not heated but rather placed directly into the calorimeter with water.  An endothermic reaction occurred with the final temperature falling down to 15.6⁰C from 21.5⁰C, meaning that the reaction mixture absorbed heat from the water.  The q of the H₂0 was found to be -1210 J, meaning that the  H of the reaction was opposite, or 1210 J, and the  H of the solution per gram of the solid sample was found to be 260 J/g.  This was obtained through dividing the  H of the reaction by the measure mass of the solid (4.7g).

In the final part of the experiment, NaOH and HCl were mixed together to determine the heat of neutralization in their reaction to produce water.  The  t was found to be 6.7⁰C using the averages of the original temperatures of HCl and NaOH.  The q of the H₂0 was found to be 1390 J, and thus the  H of neutralization had the opposite sign, being -1390 J.  The  H per mole of H⁺ and OH^- reacting is equal to the  H of neutralization, so therefore it was -1.390 kJ.

Overall, the experiment went quite well.  A note for error though can be found when the all of mixtures in the three parts had to be stirred with a stirring rod in the calorimeter.  During the stirring, the cover of the calorimeter at times opened up, along heat to enter or escape from the calorimeter.  Thus, this could have affected the observed final temperatures of the mixtures and therefore affect the  t.  Since  t is used in the equations for the q of the H₂0 and the  H for reaction, solution, and neutralization, these answers are all probably affected.  Part A. of the experiment probably also had additional error since while stirring, the bottom of the calorimeter broke, which most likely allowed heat to more drastically enter or escape the calorimeter.  Thus,  the things that were mentioned above might have an even more drastic error, and the specific heat and molar mass of the metal would be affected as well.

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