Experimental Procedure and Data

Part A: Exothermic and Endothermic Dissolution of Salts

1. In this section of the procedure, you will observe temperature changes as various salts are dissolved in water. The first salt is NaCl, and the corresponding dissolution reaction is

[latex]\text{NaCl}_{(s)}\rightarrow\text{Na}^{+}(aq)+\text{Cl}^{-}(aq)[/latex]

2. You will be recording the temperature using the Logger Pro. Insert the end of the temperature probe into the bottom of a clean, dry test tube. (Use the small test tubes).
3. Record the mass of the empty test tube prior to beginning.
4. Fill the test tube approximately 2 cm with distilled water. Record the mass of the test tube and water to determine the mass of water.
5. Record the initial temperature of the water.
6. Record the mass of a second (clean and dry) test tube.
7. Fill the second test tube approximately 1 cm with solid NaCl.
8. Pour the solid NaCl into the water and stir gently with the temperature probe.
9. Monitor the temperature. The temperature will increase or decrease away from the initial temperature. Eventually the final temperature will be reached before it begins to return to room temperature. Record the final temperature.
10. The solution should be disposed of in the CHM 111 Waste container in the back hood. Rinse and dry the test tube.
11. Repeat Steps 2-7 for CaCl₂ and (if there is time) KCl.

Part B: Calculating the Heat Capacity of a Calorimeter

1. Obtain a hot plate and plug it in.
2. Stack the two Styrofoam cups together and place inside a 400 mL beaker
3. Place the assembly on a balance. Record the mass.
4. Place 50mL of tap water in the cup assembly and record mass. Subtract to find the mass of water.
5. Place the cardboard lid on top the Styrofoam cups.
6. Set up the Logger Pro with the stainless steel temperature probe. Insert probe through hole in lid. Obtain the initial temperature of the “cold” water.
7. Attach a thermometer clamp to the probe so that the probe is not sitting on bottom of cup.
8. This is our calorimeter.
9. Tare a 150mL beaker.
10. Add ~50mL of water to beaker on scale and record weight as the weight of “hot” water.
11. Place the ~150 mL beaker on the hot plate and heat to ~90 degrees.
12. Using the temperature probe, record the temperature of the hot water.
13. Tip the lid of the calorimeter up and using beaker tongs immediately pour the hot water into the calorimeter.
14. Immediately replace the lid and begin recording temperature on the Logger Pro.
15. Gently swirl the calorimeter and measure temperature every 10 seconds until the temperature is constant for 3 readings. (The temperature will increase to the final temperature before beginning to decrease back to room temperature.) Record the final temperature in the data section.
16. Repeat steps 9-14 for a second trial.

Part C: Calculating the Specific Heat of Copper

1. Obtain the mass of ~ 10-20 pennies. Record the mass in your data table.
2. Add pennies to a large (clean and dry) test tube. Place the test tube in a 400 mL beaker containing ~ 150 mL water. The water level should be above the level of the pennies to ensure they are adequately heated.
3. Heat water to ~ 95-100 degrees C. Record this as the initial temperature of the pennies. Allow the pennies to heat for ~2-3 minutes.
4. Add your calorimeter to the balance and tare it. Add ~40 mL of water. Record the mass of the water in the table.
5. Set up your calorimeter with temperature probe as described earlier.
6. Record the initial temperature of the water.
7. Swiftly but carefully remove the test tube from the hot water bath with a pair of test tube tongs. Dump the pennies into the calorimeter and immediately cover with the lid. *Be careful that the hot water on the outside of the test tube does not drip onto your hand or into the calorimeter.
8. Monitor the temperature by taking temperature readings every 10 seconds. When the temperature is consistent for 3 straight measurements (or the temperature begins to cool) record the final temperature of the pennies and water.
9. Repeat steps 1-8 for a second trial. (Be sure to dry the pennies between trials).
10. Use the data from your table to calculate the specific heat of copper (pennies).

Pre-lab Assignment and Questions

Note – This pre-lab must be completed before you come to lab.

1. Given the balanced equation for the combustion of methane, calculate the amount of heat (q) produced by the combustion of 4.05 g CH4 using equation 2. (DHcomb = -890.4 kJ). The formula for the combustion of methane.

[latex]\text{CH}_{4(g)}+\text{O}_{2(g)}\rightarrow\text{CO}_{2(g)}+\text{2H}_{3(g)}\text{O}\,\,\,\,\,\,\,\Delta\text{H}=-890.4\text{ kJ}[/latex]

2. Consider that the 4.05 g methane is burned and all of the heat from this combustion is absorbed by [latex]1.0\cdot10^{3}[/latex] g of 20.0 [latex]^{\circ}[/latex]C water (which has a specific heat of 4.18 J g^-1 [latex]^{\circ}[/latex]C^-1). What would be the final temperature of the water?

3. A 62.5 gram sample of iron (with a heat capacity of 0.450 J/g [latex]^{\circ}[/latex]C) is heated to 100.0[latex]^{\circ}[/latex]C. It is then transferred to a coffee cup calorimeter containing 52.7 g of water (specific heat of 4.184 J/ g [latex]^{\circ}[/latex]C) initially at 20.63[latex]^{\circ}[/latex]C. If the final temperature of the system is 29.59, what was the heat capacity of the calorimeter?

4. A 17.5 g sample of metal heated in a test tube submerged in 100.0 °C water. It was then placed directly into a coffee cup calorimeter holding 49.5 g of water at 21.6 °C. The temperature of the water increased to 24.3 [latex]^{\circ}[/latex]C, determine the specific heat capacity of the metal.

5. In the above problem, if the calorimeter’s heat capacity is 21.3 J and we factored in this quantity to our calculations, what would have been the specific heat of the metal?

Experimental Data and Results

Part A: Exothermic and Endothermic Dissolution of Salts

Part B: Calculating the Heat Capacity of a Calorimeter

Show your Calculations