Average Concentration Lab Report

The average concentration of my unknown Al3+ solution (#41) was 0.02372 0.00016 mol/L. My %RSD was 0.67%, which I would say is very good. This means my precision relative to my average was very good. When calculating the mass of the precipitate, my Trial #1 and #2 were both 0.271X, with Trial #3 being 0.27XX. Having Trial #1 and #2 being only 1 decimal place different from each other was very surprising to me, and indicated high precision. This led to a low standard deviation and a low %RSD. I think consistency of observations was what led to a high precision for me. When I added reagents to the Al(NO3)3, all the trials typically had the same observations. I stopped adding things like HCl and ammonium acetate immediately after I saw a stable

(1) If the crucibles were not put in the oven at the end of the experiment, there could be excess moisture trapped in the crucible. This contributes to the mass of the weighed crucible at the end of the experiment, meaning the mass would be higher than it would normally be. After calculations, it can be concluded that the moisture in the crucible shifts the data up, creating an artificially high concentration of Al3+. (2) Reading the volumetric pipet to 25.00mL is an incredibly crucial step in this experiment because it’s the only source of Al3+ that is added to the reaction. This step affects the end result when weighing the precipitate because in the reaction, the Al3+ is the limiting reagent and is in a 1:1 stoichiometric ratio with the precipitate product. If the pipet is read too low, then the result would be an artificially low concentration because the mass would be lower. If the pipet is read too high, then the result would be an artificially high concentration because the mass would be higher. (3) On Day 3, if we did not rewash the beaker with DI water after initially pouring the solution into the crucible to be filtered, it would affect the final results of the experiment. If the beaker was not washed, not all the solution/precipitate would end up in the crucible/filtration system, which would mean a possible low reading on the mass and concentration of Al3+ because some of the precipitate would remain on the beaker. The precipitate left on the beaker would not be accounted for in the calculations, and would result in a lower measured mass and