Chmeistry Lab on Energetics

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Data collection and processing

Qualitative observation

Before
* Blue solution of copper sulfate
* Grey zinc powder

During
* Blue color solution changes to greyish black
* Heat is given out, so the surroundings become hotter.

After
* Grey powder remains on the sides of the cup
* Precipitate formed at the bottom of the cup

List of chemicals and apparatus used

Chemicals used
Copper sulfate solution, 1 mol dm-3
25g of zinc powder

Apparatus needed
Pipette, 25ml
Pipette filler
Polystyrene cup with lid
Spatula
Digital balance
Thermometer (0-100*C)
Stopwatch

Data collection

Raw Data

| Trial 1| Trial 2| Trial 3|
| Temperature/ *C±0.1|
Time/s(±0.1)| | | |
0.0| 25.6| 25.9| 25.7|
30.0| 25.6| 25.9| 25.7|
60.0| 25.5| 25.9| 25.7|
90.0| 25.5| 25.9| 25.7|
120.0| 25.6| 25.9| 25.7|
150.0| 25.5| 25.9| 25.7|
180.0| 25.5| 25.9| 25.7|
210.0| 49.4| 50.2| 51.2|
240.0| 52.2| 67.6| 56.9|
270.0| 56.5| 69.8| 61.2|
300.0| 58.9| 69.3| 63.8|
330.0| 62.5| 68.4| 67.9|
360.0| 61.7| 67.9| 68.5|
390.0| 62.8| 66.8| 66.5|
420.0| 63.2| 66.2| 65.2|
450.0| 63.9| 65.1| 64.2|
480.0.| 65.5| 64.1| 63.1|
510.0| 64.1| 63.3| 63.1|
540.0| 63.7| 63.3| 62.2|
570.0| 63.5| 62.6| 61.9|
600.0| 63.2| 62.0| 61.3|

Table showing the temperature and time for the first three trials

After this, a graph was plotted of the average temperature against time. The line produced on this graph was the extrapolated till the 170s mark. The equation of the line was found. The two equations were the equated, the downward sloping and the vertical line and the maximum temperature reached by the reaction was found. Change in temperature was found by subtracting the value obtained by the initial temperature value.

Equation of the downward line

y= -0.0064x+66.857

Equation of vertical line

x=180

Value of ∆T= -0.0064180+66.857

= 55.33*C

Processed data

Time(±0.1)| Average Temperature±0.3|
0.0| 25.7|
30.0| 25.7|
60.0| 25.7|
90.0| 25.7|
120.0| 25.7|
150.0| 25.7|
180.0| 25.7|
210.0| 50.3|
240.0| 58.9|
270.0| 62.5|
300.0| 64.0|
330.0| 66.3|
360.0| 66.0|
390.0| 65.4|
420.0| 64.9|
450.0| 64.4|
480.0| 64.2|
510.0| 63.5|
540.0| 63.1|
570.0| 62.7|
600.0| 62.2|

Table showing the average temperature reading with time.

Uncertainties
Digital balance = 5g ± 0.01g
Pipette= 25±0.05cm3
Temperature probe= 0.1*C

Calculating the value of ∆H

Volume of CuSO4=25 cm3 ∓0.05cm3

Concentration of CuSO4 used=1moldm-3

Specific heat capacity of H2O =4.18J/g℃

ΔT=40℃
The reaction was exothermic, hence:

q=-McΔT

The limiting reagent in this reaction was CuSO4 because Zn was added in excess.

Moles of CuSO4=C×V

1 × 251000 =0.025 moles

Assuming that the volume of CuSO4=volume of H2O
Also assuming that the density of water is 1gcm-3

Mass of CuSO4=1 ×25=25g

q=-McΔT

q= -0.025 × 4.18× 40

q= -6.18KJ

ΔH= qmoles= -6.180.025= -271.92KJmol-1

% uncertainty= 0.15-271.92×100=0.055%

ΔH=-271.92∓0.055%KJmol-1

Literature value= -217KJmol

%error=Experimental value-Theoritical valueTheoritical value×100

%error=-271.92+217-217×100=25.31%

Conclusion and evaluation

Conclusion
The main aim was to determine the enthalpy change for the displacement reaction: Zn(s) + Cu2+(aq) Cu(s) + Zn2+(aq)

The experiment was to determine the enthalpy change for the displacement reaction between zinc and copper. The data collected shows the relationship between time and the temperature in the reaction. As the results show, the temperature is constant till 180s because the zinc has not been added. As soon at the zinc is added, the temperature rises by about 35 degrees Celsius and then drops as time...
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