Method
In the experiment, I have been detailed the following equipment to use:
The calculation of the theoretical yield will help me during the experiment. By calculating it, I am able to tell how much the zinc oxide should weigh when the reaction is over. Also, I am able to compare it with my results to produce a graph.
To calculate the theoretical yield, you can start by dividing the amount of particles inzinc oxide (81g) by the amount of particels calamine lotion (125g). then you times it by the amount of calamine lotion you are going to use, (eg, 0.4). Therefore, 81g divided by 125g multiplied by 0.4.
In the actual experiment, we will be given 10g of calamine lotion to use. Using our quantities, we will thermal decompose the calamine lotion. Measuring out the exact amounts of calamine lotion into the test tube, we will heat it for 5minutes at first at the tip of the blue flame. After 5 minutes have passed, I will weigh it to see whether the reaction has finished. If not, I shall keep heating it for two minutes at a stretch until the reaction has finished, then record my results in a table. I will do this six times, then do repeats and take the average. This way my answer’s accuracy will be greatly improved.
During the experiment, I expect to obtain results on the yield of zinc oxide in accordance to the theoretical produce. However, I am not going to measure the amount of carbon dioxide. Instead, I will be able to see when the reaction has ceased because of the ‘bubbles’. When thermal decomposition takes place, these bubbles are made through the release of carbon dioxide. Therefore, when the bubbling has stopped, so has the reaction.
To make the experiment as safe as possible, goggles wwill be used when heating up the zin carbonate within the test tube. To stop the carbonate from spewing out of the top, I will put mineral wool just inside. This lets through the carbon dioxide, but in theory will keep in the zinc carbonate. The test tube will be fixed in an appropriate angle, so that if anything does spill out of the top, it shall not hit anyone. Also, normal lab procedures such as tying lose objects (such as hair, ties etc) back.
To make this a fair test, I will change only one variable throughout the process; the amount of calamine lotion in the test tube. Time is not a big factor, as after five minutes, the compound shall be weighed. It will be heated for two minutes at a time until the reaction has finished. The bunsen burner shall always be at the same distance of the test tube, at the tip of the ‘blue flame’ which is the hottest part. Most importantly, the amounts of calamine lotion shall be weighed nearly exact to 2 decimal places to make it as exact as possible.
I have decided to use six quantities of calamine lotion in each experiment. These shall be; 0.4g, 0.6g, 0.8g, 1.0g, 1.2g and 1.4g. This way, I shall not be using vast amounts of calamine solution. Also, there is less margin for error using smaller amounts, making my results more accurate. On top of that, I am able to do repeat experiments with the left over chemicals, so I can take an average making my results even more reliable.
Obtaining
After having done the experiment, I have gathered together the following results. In this table, I will show the results of both preliminary results and repeats and an average to go with those two. Then, tabulating the results from another group, I am able to contrast it with my own answers. Lastly, I will include the theoretical yield to show how accurate my answers are.
Analysis (see graph attached)
My results show reasonable accuracy to the theoretical yield. Combining my results with those of another group seems to have been effective, as there becomes less room for error. I was never more than 0.05g out, and in some I have matched the theoretical yield. My percentage yield has fluctuated from 100% to 113%, which I think is a good extent of accuracy.
I have noticed that my actual yields have never been below the theoretical yield, suggesting that either the reaction hadn’t quite finished, or an outside object was affecting the experiment.
Concluding this investigation, I feel that I have constucted my evidence well, having been accurate, doing repeat experiments, and averaging these out with another group. My yields have risen in accordance to the amounts of calamine ltion used, meaning that my prediction istrue to what happened. Because there is more calamine lotion, there are more particles involved, and when it thermally decomposes there will be more zinc oxide remaining. In theory, the only product that leaves the test tube will be the carbon dioxide so in ideal conditions the results should exactly match the theoretical yields.
Evaluation
The experiment has been successful because of the accuracy of my results. The procedure that I have used has been right for the nature of the investigation, and the quality of my evidence has been good. The only anomaly, if any was the experiment using 0.6g of calamine lotion. Whereas my percentage yields had varied between approximately !00% to 105%, the percentage yield in this case was 113% which is quite a long way off target for the precision that I was aiming for. To improve this, with time allowing I should have repeated the experiment a further time. The anolomaly could have been due to too much calamine lotion, but for this to happen twice is strange. However, I feel that the reliability of the evidence is sufficient enough to support the conclusion, as I have even calculated an average percentage yield, 103%. This shows that even with the anomaly, the experiment has been very precise.
To furthen the investigations scientifical merit, would have been to harness and record the amount of carbon dioxide let loose. Doing this may not be exactly accurate, but even just counting the bubbles emitted by the thermal decomposition would have given us an even better idea of accurateness.
