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  • Level: GCSE
  • Subject: Maths
  • Word count: 1540

Obtaining Zinc Oxide from Calamine.

Extracts from this document...

Introduction

Obtaining Zinc Oxide from Calamine

Calamine is a mineral containing zinc carbonate. On heating the mineral, it decomposes into zinc oxide and carbon dioxide.

 ZnCO3(s)                   ZnO(s)   + CO2(g)

This equation allows me to calculate a theoretical conversion rate of calamine to zinc oxide. But how close to this theory can be achieved in practice.

Task: To compare the theoretical conversion chart to an experimental conversion                                                                                                                                                                                                                                                                                                                                                                                      chart of calamine to zinc oxide.

To work this out we need to find out the relative atomic mass of the compounds.

 ZnCO3(s)                   ZnO(s)   + CO2(g)

65 + 12 + (16 * 3)               65 + 16 + [12 + (16 * 2)]

          125                                 81     +   44

Theoretical conversion chart

image00.png

Thermal decomposition of carbonates

Many metal carbonates decompose on heating as shown by the word equation

Metal carbonate            metal oxide + carbon dioxide

The decomposition often results in the solid being heated, changing colour and carbon dioxide being given off. The carbon dioxide can be detected using limewater.

Only the carbonates of very reactive metals do not decompose on heating.

image01.png

Plan

When heating calamine it decomposes into zinc oxide and carbon dioxide. You can tell when the calamine is hot because it turns from white to yellow, but when it is cooled, it turns back to white. This can be a method of seeing when the reaction is taking place.

To do this experiment we will weigh and measure:

image04.png        Each boiling tube and mineral wool

image04.png        Amount of calamine

image04.png        The calamine/zinc oxide in the boiling tube after every reheating

...read more.

Middle

image03.png        Put calamine in the boiling tube with mineral wool and weight accurately.

image03.png        Set up the Bunsen burner, mat and light.

image03.png        Hold the boiling tube with tongs and put over the flame keeping the calamine moving.

image03.png        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.

image03.png        Weight again on the scales and record.

image03.png        Heat again on the Bunsen burner for a few seconds, let it cool on the rack and weight again.

image03.png        Repeat until the weight of the zinc oxide remains the same.

image03.png        Repeat for different weights of calamine.

Equipment

image05.png        Boiling tube

image05.png        Mineral wool – this is to stop any calamine escaping from the boiling tube, but still letting the gases flow freely.

image05.png        Calamine

image05.png        Bench mat

image05.png        Bunsen burner

image05.png        Tongs

image05.png        Measuring scales

image05.png        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.

image06.png

Weight of zinc oxide produced

image07.png

Analysis

...read more.

Conclusion

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.

...read more.

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