experiment 5 results and discussion report: shifting equilibrium
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Nathalie Dagmang
Co-worker: Annjaneth Briones
Group 8
Date Performed: December
Results and Discussion Report 5:
Shifting Equilibrium
The calculated new equilibrium constants after the addition of different reagents determined which direction the reaction would precede. The calculated equilibrium constant for test tube number 1, for example, has a large equilibrium constant indicating that the solid is relatively soluble while the very small equilibrium constant for test tube 2 means that the solid is less soluble than that of test tube 1.
The calculated equilibrium constants are used to determine whether the reaction would proceed to the left (precipitation will occur) or to the right (dissolution will occur). Using the initial concentrations of the reagents used, the reaction quotient, Q, is calculated. The value for Q will be compared later on with the equilibrium constant. When this value exceeds that of keq, the reaction precedes to the left, forming a precipitate. This can be explained by the Le Chatelier’s Principle which says that when the Q increases, meaning the concentrations on the product side increase, the equilibrium shifts to the direction where it would consume the added concentrations, bringing back the reaction to its equilibrium state.
In part B of the experiment, reagents of different natures were added to sodium chloride to test which direction the reaction would precede in various solvents. In the first test tube, 95% ethanol was added, causing the solution to form bubbles. This can be explained from the strong solubility of the solutions caused by the strong Intra-molecular forces of attraction between the compounds. The dipole “nature” of ethanol makes it able to mix with sodium chloride which is an ionic molecule. In the second test tube, concentrated hydrogen chloride was added. There was no visible change due to the common ion effect (where the added reagent contributes to the concentration of the products) which shifts the reaction to the left, preventing the dissolution of sodium chloride. Lastly, in the test tube 3, MgSO4 was the reagent added which caused the formation of crystals (which eventually dissolved in the solution). This can be explained by the ion-pair formation which occurs when the ions of the reagent carry multiple charges. Theoretically, ion pair formation increases the solubility of slightly soluble salts.