Hess's Law Lab

Below are some of high points that I want to discuss about the Hess's Law lab.

• The water of the solutions is what captured the heat of the reaction. This remained constant at 100.0 mL (50.0 mL of one solution added to 50.0 mL of the other solution) for each trial of the lab. For calculation #1 of the analysis, mass is needed for q = s x m x delta T. Since the solutions are not pure water, the mass is determined by multiplying the total volume of solutions (after adding them together) with the density of the combined mixture. Since the mixture was mostly water, we did use the specific heat of water.


• The intent of the lab was not to prove the conservation of energy. There was a systematic error of heat being lost to the surroundings. This was true for all trials, so this factors itself out for the purpose of the lab. The only intent of the lab is to prove that achieving a heat of a reaction can be achieved through one step or multiple steps, given that the net of the multi-step approach is the same as the direct approach in terms of the same reactants and products.


• As indicated by the pre-lab, hypothetically, the sum of the heats of reaction for reactions #2 and #3 are supposed to equal the heat of reaction for reaction #1. Systematically across the board, this did not turn out to be true. The reaction #3 (hydrogen ions with ammonia) went way off the chart. I have a theory as to why. The ammonia solution used to make the 2.0 M solution for the lab was very old. Because water has evaporated from the solution over time, traces of some precipitate can be seen floating in the solution. It is my theory that as the reaction occured, the precipitate from the ammonia solution dissolved. As you will find out later this semester, some processes of dissolving are quite exothermic. This is my proposition for the undesirable results.


• I will be performing the experiment myself with new solutions. I will be giving you a write-up to place with this lab in your portfolio describing the inadequacies of the lab. This way, any criticism of your results can be placed upon the situation, not your abilities.


• IT IS NOT YOUR RIGHT TO FUDGE THE RESULTS TO MAKE IT FIT THE THEORY. IT IS YOUR RESPONSIBILITY TO PRESENT THE RESULTS "AS IS" AND EXPLAIN ANY DISCREPENCIES IN HOW THE THEORY AND DATA DO NOT COINCIDE. THE RESULTS ARE WHAT THEY ARE. SCIENCE HAS NEVER PROGRESSED BY MANIPULATING RESULTS TO GET THE DESIRED AFFECT. YOU WILL GET PAID MONEY IN THE FUTURE TO FIGURE OUT THE PROBLEM AND FIX IT, SO GET USED TO IT!! And now Mr. Brueckner is stepping off his soap box. :)