IA-Enthalpy Change of Reaction - Zinc and Copper Sulphate.

II. Data Collection and Processing

Quantitative Data

Example Calculation: Finding the Final and Initial Tempeartures

Step 1. Find the linear fit model of the graph

The linear fit model of f(x)=-0.03028x+70.95 can be gained from the graph above. From the table, the initial temperature of 21.8 can be yielded.

Step 2:Find t1 from table of values

From the table of values, it can be seen that at 126 seconds, the temperature begins to rise; this is the t1 value.

t1=126

Step 3: Calculate the Final Temperature

f(x)=-0.03028x+70.95

Tf=f(126)=67.14

The change in temperature can be found through: Tf-T1

For the example calculation,

67.14-21.8=45.34

Applying the same means of calculation for trials 2,3,4,5, the results can be seen below.

*Calculation of Average Change in Temperature

Tavg=45.3+44.2+42.8+43.9+44.7=220.9/5=44.18oC

Calculating the Enthalpy Change of Reaction

To calculate the enthalpy of reaction, the following equation will be used:

=44.18oC

=25g

=6.08g

=4.181 Jg-1oC-1

=0.39 Jg-1oC-1

Hence,

-(44.18)((25)(4.181)+(6.08)(0.39))

=-4722.67J

Now, we must change the value to he correct form because the value (-4722.67J) is the enthalpy change of the reaction when 25mL of 1M CuSO4 reacts, but we want to find the enthalpy change of the reaction per mole of CuSO4 in kJ/mol.

=CV=(1mol dm-3) (0.025dm3)=0.025mol

III. Conclusion and Evaluation

Conclusion

Calculating Percentage Error:

The enthalpy change of this reaction was found as following:

 is -188.91 kJ mol-1

The theoretical value for the enthalpy change of the reaction is 217 kJ mol-1.

X100

X100

Evaluation

Potential Sources of Errors

• Although precautions were taken to minimize heat loss to the environment, since only one Styrofoam cup with a lid that did not fit perfectly was used, it was very difficult to ensure that no heat was lost from the experiment to the environment. The lid was made of thin plastic and was not airtight, so an easy pathway for heat loss was created.
• A metallic stirring chip was used in this experiment and the temperature probe was submerged into the solution. Since only a small amount of chemicals was used, the chip often clashed with the temperature probe, causing solutions to splash within the Styrofoam cup. The decreased volume of the solution impacted the experiment, as mass is part of the necessary components to calculate the change in enthalpy.
• The lid had to be open when the zinc powder was added into the solution. This is a source of uncertainty because the temperature probe had to be isolated from the solution when the lid was opened, causing a sharp plummet in the temperature graph.
• Some of the materials used, such as the temperature probe and the Styrofoam cup, had to be shared with many other students and were not always cleaned well. Therefore, there is a high chance of residual chemicals being left on equipment. Residual chemicals and water can affect the results slightly and alter the heat capacity of the system because we’re conducting calorimetric calculations.
• Although the temperature probe was displaced from a firm ring stand, the temperature probe was not always located at the center of the solution. When the temperature probe is located closer to the bottom of the Styrofoam cup, the probe would naturally pick up higher temperature, while when it is closer to the top of the solution, the temperature would be lower.

Improvements

•  Two or more Styrofoam cups, or other cups with better heat retention ability can be used.
•  A hexagonal stirring rod can be used to minimize the clash between the temperature probe and the stirring rod.
•  The graph can be stopped for the split second while the lid is open to minimize the impact of the opening of the lid on the graph. Also, a better lid with airtight and temperature retention ability can be used.
• Acetone cleaner may be used to clean the equipment due to its high volatility and a dryer could be used to make sure that all equipment are well dried and isolated.
• More solution can be used for the experiment, allowing more distance between the bottom of the solution and the top. This way, the temperature probe can have a larger leeway and be placed in the center.