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Historical Fiction for children.
Anne Hindenberg
Chemistry Internal Assessment
DETERMINTATION OF THE ENTHALPY CHANGE FOR THE DISCPLACEMENT REACTION BETWEEN ZINC AND COPPER SULFATE
DCP AND CE
Aim: To determine determine the the enthalpy enthalpy change change for the single displaceme displacement nt reaction reaction betwee bet ween n zinc zin c and copper cop per sul s ulpha phate: te: Zn (s) (s) + CuSO CuSO4 4 (aq) (aq)
Cu (s) + ZnSO4 (aq)
Anne Hindenberg
Chemistry Internal Assessment
Contents
Raw Data…………………………………………………………………………………3
Observations…………………………………………………………………….………4
Graph………..……………………………………………………………………………5
Calculations……………………………………………………………………………6 -7
Conclusion ………………………………………………………………………………8
Evaluation……………………………………………………………………..…………9
Works Cited………..…………………………………………………………………...10
Page 2 of 9
Anne Hindenberg
Chemistry Internal Assessment
Raw Data
Table 1.0 – Table to show raw data collected for temperature increase Data Recorded
Before adding the Copper Sulfate and the Zinc Powder together, the copper sulfate is an electric blue colorless color, whilst the zinc power is a black color.
The Zinc power immediately reacts with the Copper Sulfate solution, which becomes noticeably warmer. With the zinc being in powder form, the reaction begins in almost instantaneous with minimal stirring. At the beginning the solution has a green/blue color. After the zinc has dissolved, it becomes a dark murky brown/black color. After the solution was removed from the cup, copper (redbrown) precipitates at the bottom, having been displaced by the zinc.
Graph
Page 4 of 9
Anne Hindenberg
Chemistry Internal Assessment
Figure 2.0 – Change in temperature when Zinc powder is added to Copper sulfate solution
Change of Temperature 40 35 ) C ° 30 5 . 0 ±25 ( e r 20 u t a r e15 p m e10 T
The blue lines are showing the line of best fit to estimate what the maximum temperature would have been, but as the lid had to be lifted to add the zinc, heat was lost.
Page 5 of 9
Anne Hindenberg
Chemistry Internal Assessment
Calculations
Knowing the amount of CuSO ₄ as well as its heat capacity, we can calculate the enthalpy change for this reaction using the formula: Enthalpy change = - (mass of water x specific heat capacity x temperature change)
ΔH = m x c x Δt
Mass of water (g) = volume of copper sulphate solution (cm3)
As this reaction is exothermic, i.e. heat is released the enthalpy change is negative: ΔH = - 121 kJ molˉ'
I ended up using the line of best fit (you can see the lines on the graph on page 5) to estimate the change in temperature upon adding the zinc in an ideal situation, where there would have been no heat loss. The gradient shows the rate in which the temperature decreases. We use the best –it line to estimate the change in temperature upon adding zinc in a perfect situation, where no heat would be lost. The gradient shows the rate,
Page 6 of 9
Anne Hindenberg
Chemistry Internal Assessment
at which the temperature decreases. The steep gradient at the time when zinc was added indicates that the speed of reaction, I.e. change in temperature per unit time was very high.
To calculating the percentage error (which is the difference between the theoretical and actual values) with the formula The percentage error which I achieved was =
()
()
, which is a
reasonably high percentage error. Some of the percentage error could be put down to
Mass of zinc: 3.0 g ± 1.7%
Volume of acid: 25 ml ± 0.4%
Temperature change: 28.9 C ± 0.2%
Up to 2.3% could be the error of measurement. The biggest contribution to the experimental error most likely is the heat, which was lost to the surroundings.
Page 7 of 9
Anne Hindenberg
Chemistry Internal Assessment
Weaknesses and Limitations
The experiment was not repeated and averaged to reduce the impact of any random errors and to reduce uncertainty.
The interval of readings equal to once every 30 seconds may not be sufficient to gain enough data - more frequent measurement would have given a more reliable graph. Some heat was lost to the surroundings and therefore measured temperature values would not be accurate. This probably contributed the most to the experimental error being at 44.5% and therefore would be the biggest weakness of this experiment that would need to be addressed in particular.
Measurement of 25 ml of copper sulphate had higher uncertainty because of meniscus measurement uncertainty
Zinc might have had impurities and the styrophome cup might have had traces of other reactants that introduced random error to the measurements
Suggestions for improvement
Experiment could be conducted several times and then all the values averaged to reduce the impact of anomalies and random errors.
Insulations would be useful. Coating and insulating material that would minimize the heat loss would be useful. Stirring should be done through the hole. Alternatively, the temperature of the laboratory could be adjusted, but that is less practical and more difficult to achieve
Zinc should be used in different forms and shapes to investigate how the shape of the object affects its reactivity. Different concentrations would give us information on whether concentration of reactants is directly
Page 8 of 9
Anne Hindenberg
Chemistry Internal Assessment
proportional to change in temperature and would be useful for making predictions about other similar experiments.
Measurement should be taken by the lowest point of the meniscus.
As zinc is provided by the technicians, there is not much that could be done to ascertain its purity. Possibly wash it is some acis that does not react with zinc. To prevent traces from other experiments, tubes should be washed properly before the experiment
