To do this experiment we will weigh and measure:
Each boiling tube and mineral wool
Amount of calamine
The calamine/zinc oxide in the boiling tube after every reheating
To make sure all of the calamine has reacted to form zinc oxide we will keep heating and weighing the boiling tube until the weight remains the same after each reheating. This shows that all of the carbon in the compound has reacted with the oxygen to form carbon dioxide and all that is left is zinc oxide that won’t react with the air any more.
We can measure the reaction because of the loss in weight. This is because the carbon that is reacted with the oxygen in the air has been lost into the air, reducing the weight.
To do this experiment we will change the amount of calamine we heat up. This is to product a graph so we can compare it to the theoretical graph.
To make this experiment a fair test we will:
We will use mineral wool to stop any calamine/zinc oxide escaping but still letting the gases flow freely.
Weight very carefully
Use the same scales to weight the apparatus
Repeat the heating to make sure that the entire compound has reacted.
Weight every individual boiling tube and mineral wool.
Keep the calamine moving while heating it, this is to evenly heat the compound.
Method
Weight the boiling tube and mineral wool with scales.
Put calamine in the boiling tube with mineral wool and weight accurately.
Set up the Bunsen burner, mat and light.
Hold the boiling tube with tongs and put over the flame keeping the calamine moving.
The calamine is white in colour and when it is heated and has changed to an oxide it changes colour to yellow, when it has turned yellow remove from heat and put in boiling tube to cool down.
Weight again on the scales and record.
Heat again on the Bunsen burner for a few seconds, let it cool on the rack and weight again.
Repeat until the weight of the zinc oxide remains the same.
Repeat for different weights of calamine.
Equipment
Boiling tube
Mineral wool – this is to stop any calamine escaping from the boiling tube, but still letting the gases flow freely.
Calamine
Bench mat
Bunsen burner
Tongs
Measuring scales
Boiling tube rack
Prediction
I feel that no one could get exactly the theoretical results but you could get quite close. Not accurate enough scales, incorrect weighting, and not enough heating may affect the results. I know that the results should follow the pattern of the theoretical conversion chart which shows that the more calamine heated the more zinc oxide is produced. But how precise to the theoretical amounts, I cannot be sure
Results
These are results obtained from the experiments.
Weight of zinc oxide produced
Analysis
From my results I can see that the actual amounts of Zinc Oxide produced during the experiment was very close to the theoretical amounts. Heating 0.25g of calamine produced 0.16g of zinc oxide; this is exactly the amount that the theoretical conversion chart predicted. This means that it should be possible to get exactly the amount the theoretical conversion chart predicted, this would be very difficult with fairly basic apparatus for precise experimentation.
From my graph I can see that the more calamine heated the more zinc oxide is produced. These results agree with my prediction but I did not think I could get a practical amount equal to the theoretical amounts.
Variables
There are a number of reasons for the actual percentage yield being under 100% of the theoretical yield, such as:
Not all of the calamine was fully heated
Some of the powder could have been caught in the mineral wool or on the side of the boiling tube resulting in it not being heated
Some powder could have escaped from the boiling tube before weighing
There is a possible error of 0.02g either way on the scales; so I might have misread the weight at the start or the finish.
Impurities that are volatile could make the percentage yield under 100%
Using a mass of 1g of calamine, 0.72g of zinc oxide was produced this is 110.8%. This appears to me to be an anomaly, as it appears to be the only result, which is significantly above the theoretical yield, where my other results fall on or slightly below the line of theoretical yield.
The reason for this percentage yield over 100% maybe because:
It wasn’t weighed correctly (calamine)
Somehow more calamine got into the boiling tube
The boiling tube and mineral wool was weight incorrectly or the weight of the mass of zinc oxide was weight incorrectly.
Impurities that are inert could cause the zinc oxide to be over 100% because it would not have reacted.
Evaluation
I feel that the experiment has worked quite well and I was able to show that using accurate equipment and pure compounds you could obtain exactly the same measurements as the theoretical conversion table as I obtained 100% percentage yield
The percentage yield of the experiment was: -
The percentage yield proves that the experiment worked well as it was high. Therefore proving that much of the calamine reacted.
Overall I feel that the experiment worked really well. Most of the results were very close to the theoretical amounts predicted. This made the line of best fit, fit almost exactly onto the theoretical conversion line. I think the experiment worked better than what I had expected.
I feel I tested my prediction by contrasting the theoretical with the actual and found what I had hoped.
My results fitted into the most obvious pattern that the more calamine you heat the more zinc oxide is produced. They also fitted nicely close to the theoretical conversion line. This proves it works. The line of best fit is very close to the theoretical line, therefore I can conclude that the variables [listed above] have had little effect with exception to 1g of calamine, which I consider to be an anomaly.
To improve my results I could:
Repeat the whole experiment to get an average result but this would take a lot of time.
Choose more weights of calamine e.g. 10 weights instead of only 5.
As extensions to the task you could produce a theoretical conversion graph for separating the zinc oxide. Burning it in carbon could do this; this reacts with the oxygen producing carbon dioxide (g). This would leave just zinc.
Word equation
Zinc oxide + Carbon Zinc + Carbon dioxide
Balanced symbol equation
2ZnCO3 + 2C 2Zn + 3CO2
This could be done following the calamine experiment and compare the two experiments and percentage yields.
I have plotted my results on a graph below, along with the results achieved by another group, in order to compare their results with mine. The results achieved by the other group are extremely variable, especially for the low weights. I feel that it is really impossible to mark a line-of-best-fit through the results of the other group.
It is obvious that my results were much closer to the theoretical yields than were the results of the other group.
It is true that for the highest two weights, the other group achieved yields which were relatively close to the theoretical yield. This may suggest one reason why the other group’s results were so variable. Perhaps they had difficulty weighing the calamine at the lower weights, or maybe their technique improved as the experiment continued. In discussion with the other group, I found out that, whether the weights had stabilised or not, they stopped each experiment after two ‘weighings’. I suspect that this is the real reason for the variability of their results. That is, it is unlikely that all the calamine was given sufficient time heating to ensure that a full reaction had occurred.
