Aim: To determine the enthalpy change of displacement between zinc powder and copper sulphate
Zn (s) + CuSO4 (aq) Cu (s) + ZnSO4 (aq)
Chemicals –
CuSO4 Solution ( concentration = 0.5 mol.dm3 )
Zinc (s) Powder
Data Collection –
Table 1: List of apparatus and Least Count and Uncertainties of Measuring Instruments Used
S. No.
Instrument
Unit
Least Count
Uncertainty
1.
Butter Paper
n/a
n/a
n/a
2.
Cardboard Lid
n/a
n/a
n/a
3.
Digital Laboratory Thermometer
Celsius
0.1 ºC
±0.1 ºC
4.
Digital Weighing Balance
Grams
0.001g
±0.001g
5.
Measuring Cylinder
cm3
1cm3
±0.5cm3
6.
Polystyrene Cup
n/a
n/a
n/a
7.
Digital Stopwatch
Seconds
0.01s
±0.01s
Qualitative Data
Table 2.1: Mass of Zinc Powder
Mass of Zinc (s) /M/g/±0.001g
Trial 1
0.244g
Trial 2
2.523g
Trial 3
2.416g
Table 2.2 : Collected Data
Time/t/s/±0.01s
Temperature/T/°c/±0.1°c
Trial 1
Trial 2
Trial 3
30.00
28.4
28.6
60.00
28.4
28.6
90.00
28.4
28.6
120.00
28.4
28.6
150.00
29.1
33.0
180.00
31.2
38.4
210.00
32.9
41.9
240.00
35.0
44.8
270.00
37.5
46.3
300.00
40.0
47.2
330.00
41.6
47.4
360.00
42.5
47.1
390.00
42.5
46.6
420.00
42.3
45.9
450.00
42.1
45.4
480.00
41.6
45.0
510.00
41.0
44.4
540.00
40.5
43.4
570.00
40.0
42.8
600.00
39.4
41.9
630.00
38.7
41.0
660.00
38.0
40.6
690.00
37.4
39.8
720.00
36.6
39.2
750.00
36.0
38.4
780.00
35.5
37.6
810.00
34.7
36.8
840.00
34.0
36.0
870.00
33.2
35.6
900.00
32.6
34.6
930.00
33.7
960.00
32.9
990.00
32.1
Qualitative Observation:
It was observed that when Zinc (s) powder was added to the CuSO4 solution it immediately reacted making the solution warmer .The color of the solution at the beginning was greenish in color which then turned colorless after the Zinc (s) powder had reacted. After the reaction was over, it was observed that Copper had precipitated at the bottom of the cup as a result of it being displaced by Zinc (s) powder.
Formulas:
Mass = No. of Moles (aq) x Molar Mass (s)
And
No. of Moles = Concentration x Volume
And
â-²H = Extrapolation Temperature – Initial Temperature
And
Enthalpy Change = Mass x Specific Heat Capacity x â-²H
And
Molar Enthalpy Change =
And
Mass of water = volume of copper sulphate solution
And
Percentage Deviation = x100
Trial 1:
Volume of CuSO4 (aq)
60.0cm3
Mass of Water
60g
Specific Heat Capacity
4.18 J.g‑1.ºC-1
Initial Temperature
28.4 ºC
Extrapolation temperature
53.0 ºC
Time at which Zinc (s) powder was added
120s
The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.
Calculation:-
No. of Moles of 60.0cm3 CuSO4 (aq) = (60/1000) x 0.5 = 0.03 mol
… Mass of Zinc (s) powder = 0.03 x 65 = 1.961g
However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1
â-²H = 28.4 – 53.0 = -24.60 ºC ±0.01s
Enthalpy Change = 60 x 4.18 x -24.6 = -6169.68 J = -6.16968 kJ
Molar Enthalpy Change = = -205.7 kJ.mol-1
As this reaction is exothermic i.e heat is released, enthalpy change is negative.
The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1
Percentage Deviation = x 100 = 5.2% Deviation.
Note: There were two assumptions made during this experiment.
The Specific Heat Cpacity of the solution is same as water
No Heat is lost to the surrounding
Trial 2:
Volume of CuSO4 (aq)
70.0cm3
Mass of Water
60g
Specific Heat Capacity
4.18 J.g‑1.ºC-1
Initial Temperature
28.6ºC
Extrapolation temperature
57.0 ºC
Time at which Zinc (s) powder was added
The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.
Calculation:-
No. of Moles of 70.0cm3 CuSO4 (aq) = (70/1000) x 0.5 = 0.035 mol
… Mass of Zinc (s) powder = 0.035 x 65 = 2.275g
However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1
â-²H = 28.6 – 57.0 = -28.40 ºC ±0.01s
Enthalpy Change = 70 x 4.18 x -28.40 = -8309.84 J = -8.30984 kJ
Molar Enthalpy Change = = -207.7 kJ.mol-1
As this reaction is exothermic i.e heat is released, enthalpy change is negative.
The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1
Percentage Deviation = x 100 = 4.3% Deviation.
Note: There were two assumptions made during this experiment.
The Specific Heat Cpacity of the solution is same as water
No Heat is lost to the surrounding
Trial 3:
Volume of CuSO4 (aq)
70.0cm3
Mass of Water
60g
Specific Heat Capacity
4.18 J.g‑1.ºC-1
Initial Temperature
28.6ºC
Extrapolation temperature
57.0 ºC
Time at which Zinc (s) powder was added
120s
The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.
Calculation:-
No. of Moles of 70.0cm3 CuSO4 (aq) = (70/1000) x 0.5 = 0.035 mol
… Mass of Zinc (s) powder = 0.035 x 65 = 2.275g
However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1
â-²H = 28.6 – 57.0 = -28.40 ºC ±0.01s
Enthalpy Change = 70 x 4.18 x -28.40 = -8309.84 J = -8.30984 kJ
Molar Enthalpy Change = = -207.7 kJ.mol-1
As this reaction is exothermic i.e heat is released, enthalpy change is negative.
The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1
Percentage Deviation = x 100 = 4.3% Deviation.
Note: There were two assumptions made during this experiment.
The Specific Heat Cpacity of the solution is same as water
No Heat is lost to the surrounding
Conclusion:
The displacement reaction between Zinc (s) powder and CuSO4 solution is exothermic as heat is released to its immiediate surroundings. This is supported by the calculations of all the three trials. The Zinc (s) is in powder form which reacts faster with CuSO4 solution as it has a larger surface area. By observing the graph it is found that after reaching the peak temperature, the new solutions temperature starts to decrease which means that its is loosing heat to its surrounding. The line of best fit on the graph shows the temperature change in an ideal situation. However, in reality heat is lost to the surroundings and the specific heat capacity of the solution may not be the same as water. This reaction between Zinc (s) powder and CuSO4 takes place becaude Zinc (S) powder is more reactive thancopper in CuSO4 solution. Therefore, causing copper to precipitate.
It is also possible that the concentration of the Cuso4 solution was lower , causing less energy to be released then expected.
The temperature change increases as volume of CuSO4 is increased as more Zinc (s) powder is required to react therefore releasing more energy. This is suggested by the calculations for Trial 1, Trial2 and Trial 3.
The percentage deviation of the experimental readings to the literature value is not that high suggesting few errors in the experiment. However, we attributed them to certain and possible errors.
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