Chemistry copper sulphate and zinc

My independent variable will be how much zinc I add to the solution, thus altering the rate of reaction. I will measure the rate of reaction by amount of heat given off every five seconds, then plotting temperature against time on a graph. By drawing a line of best fit through the points, we can find the gradient by using Y=Mx+C, and work out the rate of reaction from there. The dependent variables I will use are; concentration of the copper sulphate solution, the volume of the copper sulphate solution and how many times I stir up the solution. All of my dependant variables could have been used as the independent variable. I will make sure that no other forms of zinc are used in the experiment, such as blocks of zinc or stripes of zinc, as these will alter the time taken for the reaction to take place, as the active surface areas are different. The copper sulphate solution will be at room temperature (25 deg. Celsius), so all of the starting temperatures are the same. I will conduct the experiment three times in order to check my results for any anomalies.

Preliminary experiments

        I conducted preliminary experiments using 1g of zinc, in order to predict, with greater accuracy, the outcome of my experiments. It showed that the experiment was indeed exothermic, and that the temperature given off grew as the experiment progressed. I also decided that I would only time the experiments for a maximum of ninety seconds each, as this was ample time for the results to be recorded onto a graph.

Prediction

        I predict that the zinc will displace the copper in this experiment. I believe this because zinc is a more reactive element than copper, and it will therefore take the place copper to form zinc sulphate and copper. In the experiments where I am varying the quantity of zinc, the greater the amount of zinc, the greater the rate of reaction. This is because there will be more reactant for the copper sulphate to react with. When I use Avogadro's theory of moles, I believe that the zinc will not be able to be seen, because it will be in solution with the sulpher. The copper would have collected on the bottom of the cup, and a clear solution should be able to be seen. Here is, in ionic handwritten form, what I expect to happen:

Due to the volitile nature of the experiment, I will wear goggles in order to protect my eyes from anything that may enter my eyes.

Results

Results continued

Conclusion

As we can see from the graphs, as the reaction time increases, the more the reactants give off heat energy. We can tell that this experiment is indeed an exothermic reaction, by the vast amounts of heat created. From the lines of best fit (marked as ‘linear’ on the legend) we can see that one of my predictions was wrong. I predicted that the greater the amount of zinc, the faster the rate of reaction. This is untrue, as we can see from both graphs that the cup containing 1.11 grams has a slightly smaller gradient than, in the Second Experiments graph, the 0.81 grams of zinc cup. I also predicted that the greater the amount of zinc in the cup, the greater the temperature given off. This is also untrue, as we can see that the greatest amount of heat given off was 1.01 grams in the first experiment, and 0.81 and 1.01 in the second experiment. This may be due to the fact that the

Evaluation

This experiment was highly successful as it produced lots of fair results, and doing the experiment was fluidic and quick. I believe that I may have added some more insulating material to the cup if I did it a third time, such as some foil, so that heat loss was minimised further. If I were to improve my experiment, I would use the theory of moles to completely disassociate all the copper with zinc, without having excess zinc left in the cup. Unfortunately, I did not have enough time to perform this task, but it would have been very interesting to see the results. This would be a far easier and a far more accurate way to measure the rate of reaction. There would also be less anomalous results. The main factor that caused anomalous results was human error, either reading the thermometer wrong and therefore copying the results down wrong, or starting the timer at the wrong time. If I could, I would have used a machine to record the results, as this would have cut out the error. We can see from the graph titled ‘Second Experiments’ that on the 0.41 grams of added zinc, from 30 to 45 seconds there is an unexplainable dip, and then the points realign. These are anomalous results because they do not fit in with what we expected to see, which is a positive good correlation.