As the semester comes to an end I can definitely say this has been a more eventful experience than last year. As mentioned in previous posts our methodology for readying samples to be run was and is a multi-step process. The samples must first be sieved, then leached and centrifuged, separated into leachate and residue and then dried. A key component we've recently just added is neutralizing the sample using Sodium Hydroxide.
Neutralizing the sample means that we are now evaporating off just water rather than highly acidic HCl. Though, adding this step to the procedure turned out to be quite the undertaking. First, just getting the NaOH took longer than expected. In the down time Hannah, Monica and I (but really it was mostly Hannah and Monica) had the exciting task of locating and preparing samples which had yet to be run. Once the base came in we started to get to work on coming up with a way to get the pH of the solution to as close to 7 as possible. Initially we thought using an indicator would be the best route. We thought wrong. Trying to observe color change in an already colored solution which creates a black complexation as base is added is like trying to thread a needle from space. Its just not going work in a timely or efficient manner. Also considering that the base and acid are different concentrations and that the acid is reacting with carbonates within the sample means that its not the most straightforward process.
Still, we tried to create a method for this madness. Mae Kate, Monica and I started out by adding a fair amount of methyl red to our yellow solution, turning it a dirty orange. We then tried adding half the amount of acids worth of base and saw it turn immediately black and brown. Unsurprisingly, we over shot this delicate process and created a solution that was extremely basic. Which we then corrected by adding a healthy shot of dilute acid (turns out it was 10M instead of 12) which promptly brought it back down an overly acidic pH range of about 2.
After this event Amanda suggested a titration system so I went about setting one up. I found some clamps, a titration beaker and using the methyl red and a slightly expired pH meter kit, was able to correct the first sample to around 7.5 pH. The end result was an beaker of very nicely separated H2O and sample.
As this way of checking the pH of the samples was extremely tedious, Amanda was able to get us pH papers to test with. The only problem with using those is the possibility of losing some sample to the paper. In order to minimize that we're using a stirring rod and then trying to remove all drops from the rod, so that it is as dry as possible while still being damp from the solution to check acidity levels.
So thats primarily what we've been up to this semester in the lab. Perfecting this new method of leachate and residue separation. We're still working out the exact numbers to achieve neutrality, right now the easiest way to know when to stop adding base is by a significant color change. We also need to figure out the new composition of samples in regards to the metal content to salt ratio. Previously we were just accounting for Iron and Magnesium in our program calculations, but now that we're precipitating a salt there are new variables to be considered.
Until next time,