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How duration affects the rate of electrolysis in a Voltaic Cell

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Introduction

Redox Design and Experiment Design and Conduct an experiment to investigate the effect of ONE FACTOR on redox reactions. Introduction:- The two main components of redox reactions are reduction and oxidation. Reduction is a gain in electrons and the decrease in oxidation number whereas oxidation is the loss of electrons and the increase in oxidation number. Voltaic cells, also known as galvanic cells generate their own electricity. The redox reaction in a Voltaic cell is a spontaneous reaction. For this reason, voltaic cells are commonly used as batteries. Voltaic cell reactions supply energy which is used to perform work. The energy is harnessed by situating the oxidation and reduction reactions in separate containers, joined by an apparatus (known as the salt bridge which primarily completes a circuit and maintains electrical neutrality) that allows electrons to flow. The functions of a voltaic cell are quite simple. There happens to be an anode and a cathode. The positive ions go the negative electrode (anode) whereas the negative ions go to the positive electrode (cathode). Electrons always flow from the anode (where oxidation takes place) to the cathode (where reduction takes place). Electrons flow across wires whereas ions flow across the electrolyte and the salt bridge. Aim:- The objective of this experiment is to see how the time affects the mass of the zinc electrode (anode) and the copper electrode (cathode) in a voltaic cell. Variables:- Variable Type of variable How it will be controlled Time (s) Independent (The one you change) ...read more.

Middle

In this case we use this formula because we know that the zinc is being oxidized to zinc 2+ leading the zinc electrode to corrode. This therefore results in a decrease in mass of the anode (zinc electrode). Thus, it would be better for us to use the formula 'Mass change = initial mass - final mass' so that it gives us a positive value for the mass change taking place at the anode. Mass change = initial mass - final mass = > 31.29 - 31.27 = > 0.02 Table 2 -Mass changes of anode and cathode for each time interval Time (�0.21s) Mass change of Anode (Zinc electrode)(�0.01g) Mass change of cathode (copper electrode) (�0.01g) 300.00 (5 minutes) 0.02 0.03 600.00 (10 minutes) 0.15 0.11 900.00 (15 minutes) 0.21 0.22 1200.00 (20 minutes) 0.29 0.37 1500.00 (25 minutes) 0.46 0.44 1800.00 (30 minutes) 0.68 0.75 2100.00 (35 minutes) 1.04 1.03 Graph 1:- Graph 2:- To derive the equation for the two separate reactions, the number of electrons gained or lost during the process has to be deduced. The mass change per minute can be deduced from the gradient. Therefore we first calculate the gradient of graph 1 (mass changes for zinc electrode). For calculating the gradient, find two points which perfectly fits in the grid. In this case, the points (0.04. 100) and (0.08, 200) Gradient= (Y2 - Y1) � (X2 - X1) = (0.08- 0.04) � (200 - 100) = (0.04) � (100) = 0.0004 Therefore, the gradient of the first graph is 0.0002. ...read more.

Conclusion

According to the graph in the previous page, there is a very strong positive correlation between the mass change and duration of electrolysis as can be deduced from the high R squared value. The change in mass over a certain period of time is very gradual because of the size of the electrons. Although a lot of electrons are able to flow through the electrolyte, there is not such a drastic change. By looking at the graph, almost all the error bars for the points touch the line of best fit which means the data is fairly accurate. The theoretical mass of a copper electrode would be 31.75g. From the results that have been tabulated, the mass of a copper electrode is 36.21g. The percentage error can be calculated using the following formula: Percentage error = difference x 100 theoretical value = 4.46 x 100 31.75 = 14.04% This shows that although there is not such a big difference between the theoretical value and the experimental value. Evaluation Limitation Type of error Improvement The mass of the anode was not measured therefore the rate of electron transfer between the two electrodes could not be determined. This could have increased or decreased the mass of the cathode. Random Measure the mass of the anode The power pack has internal resistance therefore not all the current was emitted. This could have decreased the current, thus decreasing the number of electrons produced. Random Use a resistor to accurately measure the current The top pan balance had a zero offset error. This could have increased the mass of the cathode. Systematic Use the top pan balance with the 0.001 uncertainty to obtain more accurate values. ?? ?? ?? ?? ...read more.

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