The mass of zinc that I will be taking readings from are: 0.1g, 0.2g, 0.3g, 0.4g and 0.5g. For accurate results, I will be taking three repeats for each mass.
The factor that I will be keeping constant is the volume of copper sulphate which will be 50cm cubed. The reason I will be using 50cm cubed is because I need the maximum amount of zinc to completely react with the copper sulphate.
Method.
I will pour 50cm cubed of copper sulphate in a polystyrene cup. The reason I will be using a polystyrene cup is because it doesn’t conduct heat therefore any temperature rise will be recorded on the thermometer. I will place a thermometer in the copper sulphate for 1 minute to record the initial temperature. Once I have recorded this temperature which will be around room temperature (22degrees Celsius), I will then add the correct amount of zinc powder to the CuS04 and stir for a few minutes. I will record the final temperature of the reaction and record it.
I will subtract the initial temperature from the final temperature in order to find the temperature rise. Using this temperature rise, I will calculate the energy released using the formula MC T.
M= mass of zinc
C= constant specific heat capacity of water 4.18
T= temperature rise.
Preliminary experiment.
I carried out the experiment as shown in the method and obtained these results:
Prediction.
From my experiment I can see that as I increase the mass of zinc, the amount of energy also increases. There are no factors that I need to change in the real experiment.
Obtaining evidence.
I carried out the experiment as shown in the planning and obtained the following results:
Using the results from the table above, I will work out the energy change using the formula volume of solution x 4.18 x temp. rise.
I will now calculate the energy change/mole by: energy change
Mass of zinc.
Please see graphs.
Analysis.
When we were carrying out the experiment, I did not see a physical a reaction between the zinc and copper sulphate solution. When we added the small amount of zinc into 25ml of CuSO4, the blue coloured solution turned black in colour. I also expected the test tube to be warm during the reaction because this reaction is exothermic meaning energy is given out, but the energy given out was only enough to be recorded by the thermometer. The energy change on the thermometer was positive as shown in my results table therefore we know the reaction was exothermic.
In order for me to find the energy change within each reaction, I used the formula MC T. this stands for:
M= mass of zinc
C= constant specific heat capacity of water 4.18
T= temperature rise.
I have plotted two graphs, one of them was temperature rise against mass of zinc.
From this graph I can see that there is a direct relationship between mass of zinc and the amount of energy released when you react the zinc with CuSO4. I can tell this from the straight line graph that I obtained with the line going through the origin.
From my graph, I could pick out a few trends between mass of zinc and temp. rise:
When mass of zinc is 0.2g, temp rise is 3.1 degrees celsius.
When mass of zinc is 0.4g, temp rise is 6.2 degrees celsius.
When the mass of zinc is 0.15g, temp rise is 2.3 degrees celcius.
When the mass of zinc is 0.3g, temp rise is 4.6 degrees celsius.
As can be seen from the two trends above, as we double the mass of zinc, the energy released is also doubled therefore making the mass of zinc directly proportional to temp rise.
The second graph of which I plotted was that of which shows the relationship between mass of zinc and energy/mole. The energy per mole should be around the same value for each of the masses of zinc that we used providing we used a the same amount of copper sulphate for all the reactions. As we can from my second graph, these values are all around the same except for when the mass of zinc is 0.1g. This could be due to inaccurate measurement of the right amount of zinc because 0.1g is very hard to weigh out.
From my results table, we can see that the energy change is very small. This is because the amount of zinc that was used. Due to the small amount of zinc, there is less collision needed between the metal and CuSO4 in order to produce a zinc sulphate and copper. Zinc contains an unstable outer shell of electrons because it has the shell arrangement of 2.8.8.8.4. This means that it needs 4 electrons in order to become stable and in order for the zinc to do this, it has to displace the copper sulphate from its sulphate in order to produce zinc sulphate and copper. This reaction is very fast.
Conclusion.
From my results, I can see that my prediction was right. This prediction was “as the mass of zinc increases, so must the amount of energy released as heat”. This was due to an increased amount of particles in solution containing zinc and copper sulphate therefore there will be more full and successful collisions between the particles thus more CuSO4 bonds are broken and more ZnSO4 are being formed leaving suspended copper ions. As these bonds break, they release a lot of energy of which we recorded using the thermometer. Although in order for new bonds to be made, they need a lot of energy of which the electrons obtain from the external environment. In order for an exothermic reaction to occur, there has to be a certain amount energy induced into the reactions at first. This makes the electrons vibrate a lot. When a particle collides with this vibrating electron, It knocks it out from its outer shell thus releasing a lot of energy to the external environment because of the breakage of the intermolecular force between the nucleus and its electrons thus forming ions.
The smaller the mass of the zinc, the slower the time it took for a reaction to take place. My conclusion matches my prediction overall.
Evaluation.
I think my experiment went well because I did not obtain any anomalous results. What I did find was that the mass of zinc was directly proportional to the temperature rise although this was due to a line of best fit. The possible reasons for me to have not obtained a straight line graph through all the points is:
- The amount of zinc that we were allowed to use was very small so therefore using as little as 0.1g will require an awful lot of accuracy because what I tended to find was that I over weighed it by about 0.02g.
- When I was adding the CuSO4, I found that it was very difficult to get all the zinc in the polystyrene cup containing the CuSO4. Because of the little amount I was using, when trying to add 0.1g of zinc to the acid we will only actually end up with about 0.075 reacting.
The measures that I took to make sure that I obtained as accurate results as possible, were I used a polystyrene cup to react the zinc with the solution. This was because the polystyrene cup will insulate heat therefore heat will not be lost to the external environment, instead it is recorded on the thermometer which is what I wanted. When weighing the zinc, I again used a polystyrene container that was weightless therefore I will get the accurate proportion of zinc I required.
- In order to improve my results if I was to repeat this experiment, I would:
keep the mass of zinc constant at 0.5g and change the amount of copper sulphate used because that way weighing out the zinc will be more accurate.
- An alternative is to use 5g of zinc although this is not practical due to environmental issues.
- My experiment could have been repeated a number of times more but the time allocated did not allow me to do this.
Although I did not get a perfect graph with my line going through all my points, I feel that my graph was as accurate as I could get it, and it also accurate enough to quote my prediction.
