THERMOCHEMISTRY OF NaOH AND HCl LAB
Overview
Teacher’s Instruction: Find the Molar Heat of Reaction for the NaOH reaction. Then, predict and calculate the change in enthalpy (ΔE) and change in heat (ΔH) when 5.00g NaOH reacts completely with HCl.
Reaction Equation: NaOH(s) + HCl(aq) -> NaCl(aq) + H2O(liq)
Net Ionic Equation: Na(OH)(s) + H+(aq) -> H2O(liq) + Na+(aq)
The Big Question: If we combine solid NaOH and aqueous HCl, how will the temperature change? What will the change be with, specifically, 5.00g of NaOH?
Scientific Background and Principle: WELL, I’ll have you know that we got our hands on a fancy-schmancy Lab Quest 2 with a temperature probe. Now this device allows us to accurately record the temperature of a given entity over a period of time; as such, by having the Lab Quest record the temperature of the system, we were able to gather the total temperature change for the reaction. In theory, the temperature should increase by 53.10o
Variables
* Independent Variable: Amount of NaOH * We had a theoretical value for temperature that was dependent on the amount of NaOH used; as such, we set our amount at a certain point to achieve that temperature. * Dependent Variable: Heat of Reaction (Temperature) * We measured the temperature of the reaction throughout its duration, which would have varied in intensity and duration based on the amount of NaOH we used * Controlled Variables * Light-- by enclosing the reaction in darkness, we prevented any possible reaction between our reactants (NaOH and HCl) and the light. If light can react in the photosynthesis reaction, I’m taking no chances. * Surrounding Temperature-- by having the reaction take place in an insulated Styrofoam-esque cup, we prevented as much heat from escaping the as we prevented from entering the system; the temperature of the cup wouldn’t skew our results. * Atmospheric Pressure-- While we didn’t actually control it ourselves, by carrying out the reaction in a building very close to ground level, it’s safe to say that the atmospheric pressure was constant enough. * Concentration of HCl-- We used a specific concentration of HCl (a 3 molar solution), ensuring that our final numbers would account for concentration.
References: Brown, Theodore L., Eugene LeMay, Jr., Bruce E. Bursten, Catherine J. Murphy, and Patrick M. Woodward. Chemistry: The Central Science, AP Edition. 12th ed. Boston, M.A.: Pearson Education/Prentice Hall, 2012. Print.
Materials
* Lab Quest 2 * Temperature Probe (+5%) * Styrofoam Container * Lid * Electronic Balance (+0.5%) * Safety Goggles * Scoopula * NaOH (about 5.00 g needed) * HCl (50 mL needed) * 200mL beaker (+5%)
Procedure Checklist * Put on proper safety equipment, wash hands, check glassware for cracks, etc. etc… I don’t think I need to specify all the basic preparation stuff that happens in every single lab we do. * Record the masses of the 250mL beaker and the styrofoam cup with the lid and temperature probe * Use the 250.mL beaker to measure out 50.0mL of the 3 molarity HCl * Take mass of beaker with HCl, subtract the mass of the empty beaker, and get the mass of the 50.0mL of HCl * Measure as close to 5.00g NaOH as possible by adding bits of NaOH to the styrofoam cup while it sits on the balance (ending up with 4.98g in our case) * Set the LabQuest to begin recording temperature over an extended period of time * Combine HCl and NaOH in styrofoam cup, immediately putting the lid on the cup and, through that action, recording the change in temperature. * Allow the reaction to continue for several minutes while still recording the temperature. * When the LabQuest has recorded a steady decrease in temperature after the initial increase, remove the data from the LabQuest and remove the lid from the cup. * Dispose of the un-reusable materials, wash the glassware, return safety wear, and return anything in the lab area to the way it was when the lab was first started. * Analyze data and draw some conclusions!
Data Analysis

Qualitative * Reaction kind of fizzled out after a little bit of work * We shook the cup, but with more force than was called for * Our reaction was set to decline when we messed it up, and it never really dropped in temperature * Made a very faint fizzling/hissing noise * Went from a white powder and clear liquid to a small amount of solid grain-like mas and more clear liquid, albeit the liquid had lots of granules floating around in it (presumably from the solid)
Calculated Data * Change in Enthalpy: -13.0kJ * Maximum Temperature Reached (Legitimately): 44.4oC (+ 5.00%) * Theoretical Temperature Change: +53.1oC * Calculated Temperature Change: +25.3oC (+ 5.00%) (after 52.7 seconds)
Evaluation
What is the temperature change of the reaction between 5.00g NaCl and 50mL HCl? We performed this little experiment of ours to answer the above question, and find said temperature change. Sadly enough, our results didn’t make as much sense as we would have liked; our total temperature change was only at +25.3oC while our theoretical change was over twice that amount. Our systematic error came out to approximately 52.4%, and the random at 10.5%. As those bits of information would lead one to believe, our systematic error was the key factor here (rather than the random error). And, from that, we can deduce that our synthetic value is NOT an accurate representation because our systematic error outweighed our random error. If you were to ask one of us as to where all this error came from, we’d all easily agree that it was our own human error. For one thing, we neglected to record the temperature of the NaCl and HCl before the reaction began; while they should have been at room temperature, the change that occurred in the time between our adding the two components and our implementation of the temperature probe might have been highly significant. Along with that, we mis-handled the concept of catalyzing the reaction with a bit of motion; we did it too late and too hard.
Looking back, things that we would change include, but are not limited to: The catalyzing of the reaction, the proper utilization of the temperature probe, the use of a graduated cylinder to measure the HCl (as opposed to a regular beaker), and the haste with which we closed the lid on the reaction as it began. We definitely kept track of the variables, sure; light was easy, pressure kept itself maintained, the temperature of the room never changed, and we knew beforehand that the HCl we had was of a certain concentration.
Weaknesses of the Experiment * Catalyzing-- we needed to, and we goofed. I’m pretty sure that that has been well established over the course of this formally formatted lab analysis. * Accuracy of Instruments-- Well, while there’s bound to be SOME random error in any experiment, we actually did have the tools available to minimize said error much further than what we did. Graduated cylinders come to mind, as well as that nifty balance that records data more accurately than the one we had. * Time Constraints-- We actually screwed ourselves pretty badly in our first attempt on the experiment; as such, we felt very rushed when we managed to gain some observations in the second experiment. This might have accounted for some of the errors we experienced in our final experiment as well; who knows what we missed in our hurry? The most important weakness here was by far the lack of catalyzation. Seriously, we completely missed that part of the instructions given on the day we were to execute this lab; someone even attempted to inform us of our error, but we (and by that I mean I) brushed him off on the assumption that he was just messing with us.
Reflective Analysis Was our experiment precise? Well, technically, precision doesn’t apply as we only partook in one successful trial (and even that is debatable). So, we were definitely consistent in our findings; every trial we performed came up with the same answer (albeit that was one trial and one answer, but I’ll take what I can get). How did we address precision in our experiment? Well, we kind of didn’t-- one trial, our one answer was very close to itself (I suppose). Was our experiment accurate? Accuracy refers to the recorded value compared to the target value. As our temperature change was not even half of the target value, it’s relatively easy to say that our experiment was not the most accurate one ever performed. And I would imagine that a simple fix for that would be to agitate the reactants in their container to ensure that the entirety of the reaction would take place at one time. And we addressed it rather poorly, not controlling the speed at which the reaction took place. And that’s kind of important.
Was our experiment well-conducted? Processing issues? For a few high-schoolers with no training or clue as to what they were doing, I’d say we met expectations. True, the lab itself proved to be inaccurate. But hey-- at least we had some data, and came up with conclusions of some kind. Some were not so lucky. Individual issues have been addressed several times-- namely the fact that the reaction itself took place over a much longer time than was necessary, making the temperature change much more gradual than we could have hoped; our max value was a lot lower than what I feel it would have been had we performed correctly. If I could run this experiment again, let me tell you exactly how things would go down. First, I’d use the most precise balance in the room, as compared to the one nearest my desk. Second, I’d first measure out my 50mL of HCl in a graduated cylinder before allowing it to react with the NaCl; better accuracy is better accuracy. We also clearly had time to run more than one trial, if our first one was so badly screwed up and yet we still came out with a final conclusion. Therefore, we should have run 2-3 in total. If one were to reproduce our results, they would have to screw up pretty badly in their experiment. The experiment itself isn’t that impossible to reproduce if done correctly, although it would be wise to add the part about catalyzing the reaction (as well as giving a proper method of doing so, though I have no idea how one would describe the act of swirling a cup about). If one were to follow the procedure step by step and include that part, they should be good pretty often. These ideas and suggestions are realistic and valid! I mean, we definitely have a graduated cylinder lying around, and I directly referenced the more precise balance several times. And changing the procedure is simple, because all it would require would be the addition of a step or two (probably one). And I wouldn’t have suggested them if I didn’t think they were worth considering.