Lab 2 / Le Chatelier's Principle

Purpose / IntroductionThe intention of this lab is to determine the effect(s) a change has on a system of

equilibrium. The changes will then be related to Le Chatlier's Principle: a system under stress will correct itself to relieve the system and bring it back to equilibrium. From the gathered change observations, the equilibrium concept will be defined in relation to Le Chatlier's Principle.

For this lab, it is safe to assume that there will be equilibrium shifting between the reactants and products when certain solutions are added to the systems. Depending on the direction of the shift, the reaction can be determined to be either endothermic or exothermic. In Part I, I expect adding HCl will cause in a shift to the right because acids remove hydroxides. As for adding Na2EDTA , I am unsure of the possible reactions. For Part II, mixing solid Na2SO4 crystals into the solution should result in an equilibrium shift to the left because more SO4

2−¿¿ is being added to the already existing amount in the mixture. And, finally when NaHSO4 is added, I believe the shift will be to the right instead because HSO4 does not preexist in the mixture.

Materials and MethodsPart I

Begin by making an ice bath in a 50mL beaker. Prepare a hot bath in a second 50mL beaker using very hot tap water. Using the 24-well plate, add drops of 2.0MMgC l2 to wells C1 to C4. Next add phenolphthalein to the four wells and stir with a toothpick. Add drops of 1.0M NaOH to the wells, stir, and record observations. Follow this by adding 6.0MHCl, stir, and record. Add more HCl until a color change occurs: observe and record. This step is repeated, but use 0.15M N a2EDTA instead. Mark an empty pipet, and suck up the mixture in C3. Attach the pipet to a spoon handle using a rubber band and place it in the hot bath. Do the same for C4, but place it in the ice bath instead: observe and record. Once 10 minutes pass, switch the pipets. When finished, pour the mixtures down the drain and thoroughly clean supplies using distilled water.

Part IIPrepare an ice bath and a hot bath in two 50mL beakers. Using the 24-well plate, add

drops of NaHSO 4 to wells A1 to A5. Add a drop of thymol blue indicator to each well and stir with a toothpick. Mix a drop of N a2S O4 in a well and compare it an adjacent well: record. Repeat this step until a color change is noted. In another untainted well mixture, add solid NaHSO 4 crystals to the NaHSO 4 and thymol blue indicator mixture; stir and compare it to the well adjacent to it: record observations. Repeat this step until a color change is noted. Mark an empty pipet and suck up an unaltered mixture; attach the pipet to a spoon handle using a rubber band and place it in the hot bath; be sure to record the temperature of the water using a thermometer. Do the same with another unaltered mixture, but place it in the ice bath; be sure to record the ice bath temperature. When changes occur in the pipets, record the type of change and the temperature the change occurs at. Compare the results to the last remaining unaltered mixture still in the well plate: record. After 10 minutes, switch pipets and record observations.

When the lab is completed, pour the mixtures down the drain and wash supplies with distilled water.

SafetyFor this experiment goggles should be worn.