-The mass of electrode, after few experiments, the mass of anode and cathode electrode will be slightly changed.
-When soaking the filter paper, the concentration of KNO3 will not be the same in every repeated experiment.
MATERIALS
METHOD
(Did you clearly describe the procedure to be followed? If you have used a method from another source have you referenced it? You cannot use a design, without modification, from another source. Are there at least 5 data points for graphical analysis? Have you specified duplicate or triplicates of data points? If using data logging equipment have you specified how to programme the logger to collect this information? It is unacceptable to have the logger collect the data without you making some decisions about how this is going to happen. Have you indicated precisely how the data will be collected, for example position of thermometer, eye level etc.)
- Use two 50ml beakers to measure 50ml of 0.5M MgSO4 and 50ml of 0.5M ZnSO4 separately, use pipette to accurate the amount of solution.
- Cut same size (0.5cmx5cm) of 3 Mg strip, and same size (2cm x 5cm) of 3 Zinc metal, then clean them until they appear metallic shine, then put Zn strip into the solution of ZnSO4 and Mg strip into the solution of MgSO4.
- Use the clamps to stable the Zn and mg, keep their immersion depth are the same.
- Cut the 3cm x10cm filter paper; completely soak it into 4M KNO3 in order to establish salt bridge, and then put each end of salt bridge into ZnSo4 and MgSo4, make sure the salt distance is same in each experiment.
- Use wire to connect both metals with voltmeter. Now the electrochemical cell is set up.
- At room temperature, use thermometers to measure and record the temperature of anode electrolyte, which is the solution of MgSO4 with metal of Mg. When reading the thermometer, the bottom of the meniscus is level with eyes. At the same time, record the voltage shows in the voltameter.
- Set up the hot plate; put the anode electrolyte MgSO4 and Mg on the hot plate in order to raise temperature of anode electrolyte.
- While anode electrolyte up to the certain temperature of 30°C, 40°C,50°C,60°C and 70°C, measure and record their average voltages.
10. Repeat the experiment above three times, measure and record the voltages at different temperature of anode electrolyte.
11. Based on the data collected from the experiments then show those data in the graph.
RISK ASSESSMENT
CHEMICAL RISKS AND HANDLING:
- Magnesium sulphate and zinc sulphate are acidic and can cause eye irritation, and it may be irritation to the skin and may cause sensitization reactions. Contact with eyes and skin should be avoided through the use of safety goggles.
- When pour the chemical, it needs to be carefully
- Regular skin contact with zinc sulphate can cause skin dermatitis; breathing zinc sulphate can result in inhalation reflex bronchoconstriction, always wear goggles and apron.
PROCEDURAL RISKS AND DISPOSAL:
- Be carefully when heating the water
- Proper eye protection (goggle) must be used during the experiment.
- Apron should be worn at all times
EMERGENCY TREATMENT:
- If chemical spilled over your body, you should take off coat and use shower, clean as soon as possible.
- If chemical spilled into your eye, you need to wash your eyes immediately, or repeat teacher.
Recording data:
Those raw data is measured by the different temperature of anode electrolyte and record its average voltage
Processing data:
Processing data given by the average voltage over three experiments based on the different temperature of anode electrolyte (Mg+MgSO4)
Graph: temp VS average voltage
Conclusion:
The progressing data table and graph show that as increase in the temperature of anode electrolyte, the average voltage will decrease. The results show no evidence to support the hypothesis, the hypothesis may be failed. Because in the electrochemical cells, since Mg is more reactive than Zn, electron will flow from the Mg electrode to the Zn2+ ions. ( Mg-- Mg2+ + 2e-; Zn2+ + 2e- -- Zn; overall given us Mg + Zn 2+ --- Mg2+ + Zn ) from its half equation, Mg is actually loss electron , and the reaction is endothermic. Since increase its temperature, its hard to loss electron, and the average voltage is actually decrease when decrease the ions that flow through the salt bridge. In this experiment, some variables were not very well controlled, it will invlove some random errors, the error has an equal chance of being postive or negative; where as the systematic error are inherent in a particular apparatus such as hot plate, the error is generally reproducible and it affects the results in the same way each time. Therefore, in this experiment, there will be some random errors, systmatic errors or even mistakes.
Evaluation:
Assume that the concentation of MgSO4 and ZnSO4 is the same, both is 0.5M, even if they are prepared solutions. This experiment was conducted with some errors, including random errors, systematic errors and mistakes.
Random errors:
It including fluctuation of the voltermeter (its uncertainties of voltermeter), the distance of salt bridge, the immersion depth of electrode, the mass change of electode and reading judgement.
- Fluctuation of the voltermeter. The voltermeter display fluctuating in the third decimal place and the voltermeter fluctuated between 0.001 and 0.002.
- The distance of salt bridge: the salt bridge should be the same, however in the experiment, the distance of salt bridge always vary , and the immersion of salt bridge in each solution is changing during the experiment, especially for the repeated experiments, the distance of salt bridge hard to control to make them all the same as expriment 1. It may affect the averge voltage in both direction.
- The immersion depth of electode: the immersion depth of electode will change a bit during experiment, especially in repeated experiment. The different immersion of electode will affect the average voltage in both direction by changing the rate of ions passing through the salt bridge.
- The size of electrode: in the repeated experiment, the size of electode is not actually the same, there are slightly difference, it will affect the ions passiong through the salt bridge, therefore affect the average voltage.
- Reading judgement: when read the voltage on the voltermeter, because the voltermeter is always fluctuating, sometimes, make judgement on picking the data that displayed on the voltermeter.
Systematic errors:
- Temperature control: when heated the electrolyte on the hot plate, since its reach the certain temperature, when turn off the hot plate, actully the remaining heat still heat the electrolyte, therefore, the actually temperature will always be a liitle bit higher than recording data. it will affect the average voltage, the results may be a little bit lower than recorded data.
- The mass change of electrode: during the experiment, the electrode will be consumed as reaction goes by, therefore, as temperature goes up, the other variable actually not well controlled, and loss mass of electrode will affect the average voltage.
Mistakes:
- Choose of voltermeter: when I choose voltermeter, the percison of voltermeter was about ±0.2, hard to see the change of voltage, it will affect the percison of the collected data.
Since found the results almost stay the same, under sufficient time, change to more perciser voltermeter, which is digital voltermeter, with ±0.002 of uncertainties, and repeat the experiment again. Because of this choosing equipment mistake, waste lots of times.
- In the design, mentioned that using clamps to stable the electode, actually, it was unable to use clamp to control the immersion depth of electode in the electrolytes.
- In previous design, was tends to use hot water bath to increse the temperature of electrolyte, but it was hard to stable the temperature or control the temperature.
During the experiment, changed its method that used to heat electrolyte by using hot plate.
Improvements:
This experiment was conducted with some errors, mainly is random errors, and in order to improve the outcomes, the following improvments could be made.
In order to reduce the random errors listed above the following precaution can be taken.
- Fluctuation of the voltermeter: recording its uncertainties, and repeatd the experiments serveal times.
- The distance of salt bridge: control the salt bridge, before submerge the salt bridge into electrolytes, measure the same length of salt bridge should be submerged into each electrolytes and mark it. It can help to control the immersion depth and distance of salt bridge.
- The immersion depth of electrode: same as the controlling of immersion depth of salt bridge, mark the certain length of electrode that should be immergerd, and observe the mark change on the electrode to control the immersion depth of electrode.
- Reading judgement: take several readings then average them, get the average data from the voltermeter to minizine the chance of judgement.
Systematic errors listed above can be accommodated for in the following way.
- Temperature control: even if the hot plate will still heat the electrolyte after turn off. In the experiment, when temperature nearly reach the certain value, turn off first, let the remaining heat to heat up the electrolytes, it can minizime the difference between actually temperature and recorded temperature.
- The mass change of electrode: the mass change of electrode hard to reduce, because if change the electrode every time, other varibales will alternative have slightly differnce. In order to minizining this errors is repeating its experiment.
To avoid the mistakes in future experiments the following modification can be made.
- Choose the approxiate instruments, check its percison before using them.
- Be aware of limitation of each instruments.
