Mark Riley Chemistry Lab Exam 1

Determining Enthalpy Change EXPERIMENT 1

Mark Riley Introduction: When zinc reacts with copper(II) sulphate solution in a displacement

reaction it causes an enthalpy change. The heat this change produces can be calculated by an experiment in which known amounts of the 2 substances are mixed in a vessel and the change in temperature recorded.

Aim: To determine through experiment the enthalpy change when Zinc is

added to copper(II) sulphate solution. Hypothesis: The experiment will be an accurate way of depicting the enthalpy

change of this displacement reaction. The overall enthalpy will be negative making the reaction exothermic.

Equipment: Please see page 6 of the practical manual ATP413 CHEM.2 Procedure: Please see page 6 of the practical manual ATP413 CHEM.2

Mark Riley Chemistry Lab Exam 2

Results:

𝒁𝒏(𝒔) + 𝑪𝒖𝑺𝑶𝟒(𝒂𝒒) = 𝑪𝒖(𝒔) + 𝒁𝒏𝑺𝑶𝟒(𝒂𝒒)

Table A Graph A

y = -1.0714x + 61.214

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10

Tem

per

atu

re (°

C)

Time (mins)

Temperature vs Time

Series1

extrapolation

Time (mins)

Temp (°C)

0.5 22

1 23 1.5 23

2 23

2.5 23

3

3.5 38 4 46

4.5 47

5 49

5.5 52 6 53.5

6.5 54

7 54

7.5 53

8 53 8.5 52

9 51.5

9.5 51

Mark Riley Chemistry Lab Exam 3

RESULTS / Calculations: EX2A. Number of moles zinc used

𝑛 =𝑚

𝑁

4.00

65.37= 0.061 𝑚𝑜𝑙𝑒𝑠

EX2B. Balanced equation for the reaction.

𝑍𝑛(𝑠) + 𝐶𝑢𝑆𝑂4(𝑎𝑞 ) = 𝐶𝑢(𝑠) + 𝑍𝑛𝑆𝑂4(𝑎𝑞 )

EX2C. Moles of zinc that would react with 1 mole of CuSO4

1𝑍𝑛(𝑠) + 1𝐶𝑢𝑆𝑂4(𝑎𝑞) = 1𝑪𝒖(𝒔) + 1𝑍𝑛𝑆𝑂4(𝑎𝑞) ∴ 𝑂𝑛𝑒 𝑚𝑜𝑙𝑒 𝑤𝑜𝑢𝑙𝑑 𝑟𝑒𝑎𝑐𝑡 EX2D. The excess reagent

𝑇𝑕𝑒 𝑚𝑎𝑠𝑠 𝑟𝑎𝑡𝑖𝑜 𝑜𝑓 𝑡𝑕𝑒 𝑟𝑒𝑎𝑔𝑒𝑛𝑡𝑠 𝑖𝑠 − 𝑍𝑛: 𝐶𝑢𝑆𝑂4 65.4𝑔: 159.6𝑔 𝐶𝑢𝑆𝑂4 − 0.025 𝑚𝑜𝑙𝑒𝑠 𝑥 63.54 + 32.1 + 64 𝑔 = 3.99𝑔

𝑍𝑛 − 65.4𝑔 𝑥 3.99𝑔

159.6𝑔= 1.64𝑔

EX2E. Number of moles used

1𝑍𝑛(𝑠): 1𝐶𝑢𝑆𝑂4(𝑎𝑞 )𝑒 0.025 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑢𝑆𝑂4 ∴ 0.025 𝑚𝑜𝑙𝑒𝑠 𝑍𝑛

EX2F. 𝑬𝒏𝒆𝒓𝒈𝒚 𝒂𝒃𝒔𝒐𝒓𝒃𝒆𝒅 𝒃𝒚 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝒙 𝟒.𝟐 𝒙 ∆𝑻

25 𝑥 4.2𝐽 𝑥 54°𝐶 − 22°𝐶 = 3360 𝐽𝑜𝑢𝑙𝑒𝑠 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 EX2G. Enthalpy change

𝑚 𝑥 𝑐 𝑥 ∆𝑡 ÷1000

𝑛

− 25𝑔 𝑥 4.2 𝑥 32 ÷1000

0.025= −134𝑘𝐽 𝑚𝑜𝑙−1

EX2H. Percentage error

𝑬𝒓𝒓𝒐𝒓 = 𝒆𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍 𝒗𝒂𝒍𝒖𝒆−𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅 𝒗𝒂𝒍𝒖𝒆

𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅 𝒗𝒂𝒍𝒖𝒆 𝒙 𝟏𝟎𝟎 𝐸𝑟𝑟𝑜𝑟 =

−134 +219

219 𝑥 100 = 39%

Mark Riley Chemistry Lab Exam 4

Discussion: REFER TO CALCULATIONS OR GRAPHS 25ml of copper(II) sulphate solution containing O.025 moles of copper(II) sulphate was mixed with 0.061moles(4g) of zinc EX2A. No real care was to be taken in measuring the 4g of zinc as it is by far the excess reagent. If 1 mole of copper(II) sulphate was used then only one mole of zinc should be used EX2C because the molar ratio of them in a balanced equation is 1:1 EX2B, therefore because only 0.025 moles of copper(II) sulphate was used, only 0.025 moles(1.64g) of zinc is actually needed to be used for a complete reaction EX2E. The reaction between the zinc and copper(II) sulphate was reasonably fast Graph A causing a temperature rise of 32°C Table A with the highest temperature being reached within 4 minutes Graph A The energy needed to raise the temperature of 25ml of the solution by 1°c or K is 3360 Joules EX2F. This energy comes from the difference in the heat content of the products compared to the reactants. The enthalpy change in this displacement reaction is -134kJ mol-1 EX2G therefore the reaction was exothermic because heat was given out. The accepted value for the enthalpy change in this reaction is -219kJ mol-1 which is 39% off the results achieved through this experiment EX2H. This difference was attributed to the heat loss to the surroundings during the reaction (proven by extrapolating the trend line back Graph A), errors or in the measurements (particularly of volume and temperature which was somewhat caused by limitations in the measuring equipment) and also the concentration of the copper(II) sulphate solution is assumed not to have been accurately mixed.

Conclusion: Zinc mixed with copper(II) sulphate solution caused an exothermic

reaction. The enthalpy change calculated from the results was different than the published value which we attributed to some certain and possible errors. More care needs to be taken to assure solutions are mixed properly, accuracy of measurements needs to be more precise and improvements to the vessel must be made in order to achieve results closer to the published value.

Mark Riley Chemistry Lab Exam 5

Determining Enthalpy Change EXPERIMENT 2

Aim: To modify the first experiment in an attempt to increase the accuracy

of results. Hypothesis: The improvements made to the first experiment will result in a final

enthalpy change that is closer to accepted value. Equipment: Please see page 6 of the practical manual ATP413 CHEM.2 Procedure: Please see page 6 of the practical manual ATP413 CHEM.2 with the

following modifications

Insulate the vessel (polystyrene cup) with layers of aluminum foil

Seal the vessel as best as possible using the lid with a hole to allow the thermometer access to the solution

Use a bulb pipette to measure the copper(II) sulphate solution.

Mark Riley Chemistry Lab Exam 6

Results:

𝒁𝒏(𝒔) + 𝑪𝒖𝑺𝑶𝟒(𝒂𝒒) = 𝑪𝒖(𝒔) + 𝒁𝒏𝑺𝑶𝟒(𝒂𝒒)

Table A Table B

y = -0.631x + 58.315

20

25

30

35

40

45

50

55

60

0 1 2 3 4 5 6 7 8

Tem

per

atu

re (°

C)

Time (mins)

Temperature vs Time

Series1

extrapolation

Extrapolated Trendline

Time (mins)

Temp (°C)

0.5 22

1 22

1.5 23

2 23

2.5 23

3

3.5 50

4 56

4.5 55.5

5 55

5.5 54.5

6 54.5

6.5 54.5

7 54

7.5 53.5

Mark Riley Chemistry Lab Exam 7

RESULTS / Calculations: EX2A. Number of moles zinc used

𝑛 =𝑚

𝑁

4.00

65.37= 0.061 𝑚𝑜𝑙𝑒𝑠

EX2B. Balanced equation for the reaction.

𝑍𝑛(𝑠) + 𝐶𝑢𝑆𝑂4(𝑎𝑞 ) = 𝐶𝑢(𝑠) + 𝑍𝑛𝑆𝑂4(𝑎𝑞 )

EX2C. Moles of zinc that would react with 1 mole CuSO4

1𝑍𝑛(𝑠) + 1𝐶𝑢𝑆𝑂4(𝑎𝑞) = 1𝑪𝒖(𝒔) + 1𝑍𝑛𝑆𝑂4(𝑎𝑞) ∴ 𝑂𝑛𝑒 𝑚𝑜𝑙𝑒 𝑤𝑜𝑢𝑙𝑑 𝑟𝑒𝑎𝑐𝑡 EX2D. The excess reagent

𝑇𝑕𝑒 𝑚𝑎𝑠𝑠 𝑟𝑎𝑡𝑖𝑜 𝑜𝑓 𝑡𝑕𝑒 𝑟𝑒𝑎𝑔𝑒𝑛𝑡𝑠 𝑖𝑠 − 𝑍𝑛: 𝐶𝑢𝑆𝑂4 65.4𝑔: 159.6𝑔 𝐶𝑢𝑆𝑂4 − 0.025 𝑚𝑜𝑙𝑒𝑠 𝑥 63.54 + 32.1 + 64 𝑔 = 3.99𝑔

𝑍𝑛 − 65.4𝑔 𝑥 3.99𝑔

159.6𝑔= 1.64𝑔

EX2E. Number of moles used

1𝑍𝑛(𝑠): 1𝐶𝑢𝑆𝑂4(𝑎𝑞 )𝑒 0.025 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑢𝑆𝑂4 ∴ 0.025 𝑚𝑜𝑙𝑒𝑠 𝑍𝑛

EX2F. 𝑬𝒏𝒆𝒓𝒈𝒚 𝒂𝒃𝒔𝒐𝒓𝒃𝒆𝒅 𝒃𝒚 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 = 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝒙 𝟒.𝟐 𝒙 ∆𝑻

25 𝑥 4.2𝐽 𝑥 56°𝐶 − 22°𝐶 = 3570 𝐽𝑜𝑢𝑙𝑒𝑠 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 EX2G. Enthalpy change

𝑚 𝑥 𝑐 𝑥 ∆𝑡 ÷1000

𝑛

− 25𝑔 𝑥 4.2 𝑥 34 ÷1000

0.025= −142𝑘𝐽 𝑚𝑜𝑙−1

EX2H. Percentage error

𝑬𝒓𝒓𝒐𝒓 = 𝒆𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍 𝒗𝒂𝒍𝒖𝒆−𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅 𝒗𝒂𝒍𝒖𝒆

𝒂𝒄𝒄𝒆𝒑𝒕𝒆𝒅 𝒗𝒂𝒍𝒖𝒆 𝒙 𝟏𝟎𝟎 𝐸𝑟𝑟𝑜𝑟 =

−134 +219

219 𝑥 100 = 35%

Mark Riley Chemistry Lab Exam 8

Discussion: REFER TO CALCULATIONS OR GRAPHS 25ml of copper(II) sulphate solution containing O.025 moles of copper(II) sulphate was again mixed with 0.061moles(4g) of zinc EX2A but this time the solution was measured using a bulb pipette instead of a plastic measuring cylinder to improve the accuracy of the measurement. No efforts were made to improve the accuracy when measuring the 4g of zinc because as discussed in experiment 1, zinc is by far the excess reagent and only 1.6g is actually needed EX2D. The vessel which was a polystyrene cup was insulated with layers of aluminum foil to reduce heat loss to the surroundings. A lid was also placed onto the polystyrene cup to seal the vessel in a further attempt to contain heat reducing heat loss to the surroundings. Although these changes did not have a large affect on the overall results, the attempt to contain heat was somewhat successful as can be seen when comparing Graph A from experiment 1 to Graph A from experiment 2. Comparing the temperature decrease after the highest temperature was achieved for both experiments Table A vs Table A proves the effectiveness of the efforts made to prevent heat loss to the surroundings. More proof of this effectiveness can be found by comparing the difference between the highest temperature reached to the value given by extrapolating the trend line back on the graphs for each experiment Graph A Graph A and comparing the 2 differences (difference is smaller for experiment 2). The results from the 2nd experiment show a slightly higher temperature change Table A vs Graph A which resulted in an increased kJ/mol ratio. The percentage error decreased in comparison to the results from the first experiment EX2G but was still 35% off the published results EX2H. The explanation for this difference in values remains the same as in the first experiment even though as explained, changes were made somewhat successfully to this 2nd experiment to minimize errors.

Conclusion: After accounting for possible errors and making changes in order to maximize

the accuracy, the experiment was repeated and the results showed an enthalpy change closer to the published value but still significantly lesser. This can be accounted for by the same reasons as experiment 1.