Spill Plan - Neutralizing an NaOH Spill in Seawater
Prince of Wales Secondary
Floor Location : M 122 V
In this experiment, a methodology to predict the amount of HCl required to neutralize an NaOH spill in seawater was tested. This project is important because the Canadian Coast Guard has research and response plans for oil spills but lacks research and response plans for chemical spills. It was hypothesized that a spill of NaOH in seawater could be neutralized by adding a calculated amount of HCl, with the calculation based on the assumption that one mol of HCl would neutralize one mol of NaOH. This hypothesis was tested through a titration of HCl into a simulated NaOH spill in seawater, using thymol blue as the indicator and a UV-VIS spectrophotometer to measure the molar absorptivity of the HL- and L2- chemical species of thymol blue. In order to calculate the pH, the molar absorptivity coefficients and pKa of thymol blue in salt water were required, so these constants were found through a separate titration using the UV-VIS spectrophotometer and software analysis. Using these values and the spectrophotometric data from the titration of HCl into the simulated NaOH spill, the pH was calculated at each point in the titration. However, it was found that only 17% of the predicted amount of HCl was needed to neutralize the spill. It was theorized that this was due to most of the NaOH reacting with metal ions and HCO3 in seawater to form precipitates before the HCl was added. This theory was tested through a side-experiment which was ran in the same way as the initial experiment, but instead of using seawater, used a “Lab Water” solution of NaCl and double-distilled MilliQ water. In the side experiment, the amount of HCl needed to neutralize the Lab Water NaOH spill was within 0.9% of the predicted amount, supported the theory. From this understanding, an alternative approach for calculating the amount of HCl required to neutralize an NaOH spill in seawater was determined, which was based on analysis of samples of post-spill seawater. A practical in situ procedure was then proposed which uses this new approach and that is expected to be effective regardless of the amount of NaOH that reacts with ions in seawater to form precipitate. These results and the proposed in situ procedure could be used by the Canadian Coast Guard, Transport Canada, or marine institutes as a basis for further research.