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Lab Report Assistant
This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.
Exercise 1: Testing Hess’s Law
Data Table 1. Temperature (°C) of the Solution (NaOH + HCl).
|
Initial Temperature of NaOH (°C) |
24.8 |
|
Initial Temperature of HCl (°C) |
24.9 |
|
Average Initial Temperature of Two Separate Solutions (°C) |
24.85 |
|
Highest Temperature of Mixture (May Be Extrapolated from Graph) (°C) |
35.9 |
|
Change in Temperature of Mixture (°C), ΔT |
9.2 |
Data Table 2. Temperature of Solution Every 20 Seconds.
|
Time after mixing (min:sec) |
Temperature (oC) |
|
Initial |
26.7 |
|
0:20 |
35.4 |
|
0:40 |
35.9 |
|
1:00 |
35.8 |
|
1:20 |
35.9 |
|
1:40 |
35.9 |
|
2:00 |
35.8 |
|
2:20 |
35.7 |
|
2:40 |
35.6 |
|
3:00 |
35.5 |
|
3:20 |
35.3 |
|
3:40 |
35.1 |
|
4:00 |
35.0 |
|
4:20 |
34.9 |
|
4:40 |
34.7 |
|
5:00 |
34.6 |
Graph 1. Reaction 1 (NaOH + HCl).
|
Graph (NaOH + HCl) |
|
|
Data Table 3. Temperature (°C) of the Solution (NaOH + NH4Cl).
|
Initial Temperature of NaOH (°C) |
24.9 |
|
Initial Temperature NH4Cl (°C) |
25.6 |
|
Average Initial Temperature (°C) |
25.25 |
|
Highest Temperature of Mixture (May Be Extrapolated from Graph) (°C) |
26 |
|
Change in Temperature of Mixture (°C), ΔT |
2.3 |
Data Table 4. Temperature of Solution Every 20 Seconds.
|
Time after mixing (sec) |
Temperature (oC) |
|
Initial |
23.7 |
|
0:20 |
25.3 |
|
0:40 |
25.5 |
|
1:00 |
25.8 |
|
1:20 |
26 |
|
1:40 |
25.8 |
|
2:00 |
25.7 |
|
2:20 |
25.8 |
|
2:40 |
25.7 |
|
3:00 |
25.7 |
|
3:20 |
25.8 |
|
3:40 |
25.8 |
|
4:00 |
25.7 |
|
4:20 |
25.7 |
|
4:40 |
25.7 |
|
5:00 |
25.7 |
Graph 2. Reaction 2 (NaOH + NH4Cl).
|
Graph (NaOH + NH4Cl) |
|
|
Data Table 5. Temperature (°C) of the Solution (NH3 + HCl).
|
Initial Temperature of NH3 (°C) |
25.7 |
|
Initial Temperature HCl (°C) |
25.3 |
|
Average Initial Temperature (°C) |
25.5 |
|
Highest Temperature of Mixture (May Be Extrapolated from Graph) (°C) |
32.8 |
|
Change in Temperature of Mixture (°C), ΔT |
7.6 |
Data Table 6. Temperature of Solution Every 20 Seconds.
|
Time after mixing (sec) |
Temperature (oC) |
|
Initial |
25.2 |
|
0:20 |
32.5 |
|
0:40 |
32.7 |
|
1:00 |
32.8 |
|
1:20 |
32.7 |
|
1:40 |
32.6 |
|
2:00 |
32.4 |
|
2:20 |
32.3 |
|
2:40 |
32.1 |
|
3:00 |
32 |
|
3:20 |
31.9 |
|
3:40 |
31.8 |
|
4:00 |
31.7 |
|
4:20 |
31.6 |
|
4:40 |
31.5 |
|
5:00 |
31.4 |
Graph 3. Reaction 3 (NH3 + HCl).
|
Graph (NH3 + HCl) |
|
|
Questions
A. What were the starting temperatures for each of the reactions? Use the scatter plots in Graph 1, Graph 2, and Graph 3 to support your answers.
26.7
23.7
25.2
B. Calculate the heat loss or heat gain of the 3 solution mixtures (qrxn). Then calculate the ΔH for each reaction. Show your calculations.
C. Use Hess’s Law to determine ΔH for the first 2 reactions and then add them together to determine ΔH for the third reaction: NH3 + HClà NH4Cl.
D. Compare the results of question “C” with the experimental results of the reaction:
NH3 + HCl à NH4Cl (calculate the percent difference).
E. Use the thermodynamic quantities given below to calculate the theoretical ΔH for this reaction: NH3 + HCl à NH4Cl
· ΔH°f for NH3 (aq) = - 80.29 kJ/mol
· ΔH°f for HCl (aq) = - 167.2 kJ/mol
· ΔH°f for NH4+(aq) = - 132.5 kJ/mol
· ΔH°f for Cl- (aq) = - 167.2 kJ/mol
F. What was the percent difference of the various methods used when comparing the results of Hess’s Law method and the experimental results to the theoretical value?
G. Were the reactions performed in this laboratory exercise exothermic or endothermic? How could you determine this?
H. Define Hess’s Law. Did your experimental results support Hess’s Law? Use your data to explain your answer.
I. What are some possible sources of error in this experiment?
