Hypothesis: some metal carbonates decompose more easily than others when they are heated.
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Thermal decomposition of carbonates Introduction: Carbonates decompose when they are heated, producing calcium oxide and carbon dioxide. Carbon dioxide can be detected using lime water. Calcium carbonate calcium oxide + carbon dioxide CaCO3 CaO + CO2 Other metal carbonates decompose in the same way. Here are the equations for the thermal decomposition of copper carbonate: copper carbonate copper oxide + carbon dioxide CuCO3 CuO + CO2 Hypothesis: some metal carbonates decompose more easily than others when they are heated. Aim: The times taken for a chemical reaction to take place metals high up in the reactivity series (such as calcium) have carbonates that take a lot of energy to decompose them. Metals low down in the reactivity series (such as copper) have carbonates that are easily composed. This is why copper carbonate is often used at school to show these reactions. It is easily decomposed and its colour change, from green copper carbonate to black copper oxide, it is easy to see. Risk Assessment Lime water Copper carbonate Spillages Bunsen burner Boiling tubes Hair General lab safety rules Can cause skin to go red or blistered.
Heat the carbonates till lime water turns milky, keeping track of time. Lift the delivery tube from the limewater before the heating is stopped. This is to avoid suck-back. Write down all observations. Notice what happens to the limewater and how long it takes to turn milky. Notice whether any melting occurs in the heated test-tube and any colour changes taking place. Repeat the experiment with the other metal carbonates supplied, and in each case write down your observations. Carbonates Reaction Time Zinc Carbonate Turned yellow after a few seconds then turned black. Turned yellow Turned yellow 2 minutes 2 minutes 2 minutes Calcium Carbonate Lime water turned cloudy after a minute No change but gas is produced in the boiling tube No change 2 minutes 2 minutes 2 minutes Copper Carbonate Turned black Turned black Turned black 2 minutes 1 minutes 49 seconds 2 minutes Anomalies These are results that are abnormal and random. The anomalies on my results are circled. The reasons for these are a random or human error.
The experiment was easy to set up but it was difficult to heat the carbonates the same way each time as the clamp was constantly moving whenever we removed the boiling tube but did not seem to affect the results as they were all accurate. Some of the powder did not reach the bottom of the boiling tube which means that it would not get heated as strongly and would take longer to decompose. The hypothesis taught me that some metal carbonates decompose more easily than others when heated. Equipment Measuring cylinder 3x boiling tubes 2x delivery tubes 1x spatula Teat pipette Bunsen burner Heat proof matt Stand Clamp Stopwatch Test tube rack Lime water Calcium Carbonate Copper Carbonate Zinc Carbonate For measuring limewater For putting metal carbonates in To carry carbon dioxide into lime water To transfer metal carbonates To transfer limewater safely To heat the metal carbonates To stop the surface burning To hold the clamp Attaches to the stand and holds the boiling tubes To measure two minute intervals To hold the test tubes To check for Carbon Dioxide To test the hypothesis To test the hypothesis To test the hypothesis
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Here's what a teacher thought of this essay
A reasonable write up which has a good beginning and method. It however loses momentum in the last section and does not give suggestions how the method could be improved. 3 Stars.
Marked by teacher Louise Star 21/06/2013
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