In the third reaction, solid sodium hydroxide reacts with aqueous hydrochloric acid to form water and aqueous sodium chloride: NaOH (s) + H + (aq) + Cl – (aq) → H 2 O (l) + Na + (aq) + Cl – (aq) ∆ H 3 = ? As in the first part of the Thermochemistry lab, you will use an EPS cup supported in a beaker as the calorimeter. Although this assembly is not a perfect insulator, if we assume that the heat losses are not significantly different from one trial to the next, we can expect valid comparisons. PROCEDURE: Be sure to read the Safety and Disposal section at the end. Reaction 1 1. Insert the thermometer through a slit rubber stopper. Clamp the stopper to a ring-stand to suspend the thermometer in a vertical position. 2. Measure 100.0 mL of DI water into the cup. Place the thermometer in the water. 3. Weigh the provided vial of NaOH pellets. Because sodium hydroxide readily picks up moisture from the air, you should weigh it quickly and go on to the next step without delay. CAUTION: Solid sodium hydroxide and NaOH solutions are quite caustic. Avoid skin contact, and wash thoroughly in the event of an accidental exposure. 4. As it may take some time for the thermometer to come into thermal equilibrium with the solution, wait until you have at least three subsequent readings (at 15 second intervals) at the same temperature before adding the solid NaOH to the water in the calorimeter cup. Be sure to stir the pellets in the solution with a glass stirring-rod, to encourage complete dissolving. Collect data for a full 225 s, or at least until the temperature readings begin to drop after passing through a maximum value. 5. After collecting the temperature data, weigh the empty vial (with its cap) and record the mass of NaOH used in your experiment. Dispose of the solution into the proper waste container. Rinse the thermometer, the cup, and the stirring rod with DI water, then dry them in preparation for the next reaction. 6. Read through the data to find the initial solution temperature, T 1 , and the maximum solution equilibrium temperature, T 2 . . Record T 1 and T 2 on your data sheet. Note : You may want to graph the data to determine the maximum equilibrium temperature.
CHM151LL: T HERMOCHEMISTRY | 7 Reaction 2 1.Repeat steps 1-6, initially measuring out 50.0 mL of 1.0MHCl (not water) into the calorimeter cup. In step 3, measure 50.0 mL of 1.0MNaOH solution (not solid NaOH) into a clean dry graduated cylinder. After the temperature readings reach a steady value in the HCl solution, add the 1.0MNaOH solution to the calorimeter.Reaction 3 1.Repeat steps 1-6, using solid NaOH again, but measuring out 100.0 mL of 0.5MHCl solution instead of water. Data Analysis 1.Calculate the total mass of solution, m, for each of the reactions. Assume a density of 1.00 g/mL for water and 1.02 g/mL for the HCl and the NaOH solutions and be sure to add the mass of the solid NaOH when needed. 2.Calculate the temperature change, ∆T, for each of the reactions. 3.Calculate the heat, q(in kJ), absorbed by the solution in each reaction, using: q = m·s·∆T
You've reached the end of your free preview.
Want to read all 14 pages?