LIMESTONE DISSOLUTION IN VARIOUS pH SOLUTIONS

The project was designed to assess the role of a solution’s pH on the dissolution of limestone. Five solutions with pH values of 5.01, 5.35, 5.5, 6, and 7 and were created to represent the range of pH values of rainwater (5.5) to neutral solutions observed in the environment. Solutions were created by diluting 2N HCl with deionized water. Fifty one to two inch cubes were cut from the same type of limestone, and the mass of each cube was recorded. The fifty cubes were split into two subsets of twenty-five for two experimental designs. The first subset further split the cubes into five groups of five; one group for each pH solution, allowing five replicate trials in which a beaker of solution will have one cube of limestone submerged. The cubes were submerged for 4 hours at a time:, then removed, rinsed, dried, and weighed to the thousandth of a gram. The pH values of the solutions were also measured after each 4-hour increment. Ten trials were conducted. An ANOVA indicates that the limestone cubes dissolved a similar rates regardless of the pH of the solution (F(4,245) = 0.114; p = 0.977). The pH of all of the solutions increased, with finally pH values ranging from 8.60 (initial pH of 5.01) to 8.78 (initial pH 5.5 and 6.0). However, the pH values of the final solutions were not statistically similar (F(4,245) = 4.459; p = <0.01). The similar dissolution rates of the limestones in all of the pH solutions appear to be a function of the ionic strength of the solutions and the overall undersaturated conditions of the solutions with respect to calcite. Currently, working is examining the effect of different temperature solutions on the dissolution rates. The results from these trails will be compared to the original work to assess the role of temperature.