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Our project is to find out what products are formed when copper carbonate decomposes. Copper has 2 oxides, Cu2O and CuO. We are told that one of the following two equations are correct:
Equation 1 (Eqn1): 2 CuCO3 (s) –> Cu2O (s) + 2 CO2 (g) + 1/2 O2 (g)
Equation 2 (Eqn2): CuCO3 (s) –> CuO (s) + CO2 (g)
I have to find out which of the two are correct by experimentation. By looking at the equations, I can see that gas is given out.
Collecting this gas will be a good way to find out which equation is correct. I will collect the gas in a 100cm3 gas syringe. Therefore I want to be collecting about 80cm3 of gas per amount of copper carbonate.
Eqn1 Ratio copper carbonate : gas
2 : 2 + 1/2
1 : 1.25
Eqn2 Ratio copper carbonate : gas
1 : 1
Above states that 2 1/2 moles of gas are produced in Eqn1. I know that 1 mole of gas occupies 24000cm3 in standard room temperature and pressure. I have stated that I want to collect about 80cm3.
This means that I wasn’t to collect 80/24000 moles of gas. This is equal to 0.00333…. (recurring) moles of gas. Out of the 0.0033 moles of gas collected,
2 of them have to be moles of CO2 and 0.5 of them are moles of 02
So in Eqn1 we want 2 x 0.0033 moles of CO2 to be collected which is 0.00266… moles
According to the Eqn, the mole ratio of CuCO3 to CO2 is 2:2. This means we need 0.00266… moles CuCO3 to be decomposed in oreder to create the 80cm3 of gas.
From this we can find the mass of CuCO3 to be used, by using the formula:
Mass = moles x RFM (relative formula mass)
= 0.00266… x (63.5 + 12 + (16 x 3) )
So in Eqn1, using 0.329g CuCO3 should produce about 80cm3 gas. Using 0.329g CuCO3 in Eqn2 should give less than 80cm3 gas. I shall prove this:
CuCO3 (s) –> CuO (s) + CO2 (g)
Mass of CuCO3 – 0.329g
Moles of CuCO3 – 0.00266…
Moles of CO2 produced – 0.00266…
Volume of CO2 produced – 0.00266… x 24000 = 63.9cm3
Therefore, I know that whichever Eqn is correct, using 0.329g CuCO3 will not produce over 80cm3, and therefore the gas will definitely be able to fit into the gas syringe
This represents the syringe being held by a retort stand and also the boiling tube being held by tongues
* Weigh exactly about 0.329g powdered copper carbonate
* Set out apparatus as above
* Put copper carbonate into boiling tube and put bung on. Bung should be as tight as possible to ensure it is air tight and to minimise the amount of gas lost
* Attach delivery tube to gas syringe making sure plunger is fully depressed
* Light the Bunsen on a yellow flame for safety and then turn it to a blue flame when ready to begin experiment
* Apply Bunsen burner under boiling tube, wafting it under the copper carbonate
* I know when the reaction has stopped by when the copper carbonate has gone red or black (depending whether Cu2O or CuO is produced).
* Also, when the reaction stops, the plunger on the gas syringe will stop moving
* It might be necessary to wait to let the syringe and its contents to cool down so that the gas occupies the correct volume
I need to make sure the experiment is fair to ensure accurate results. From past experience, I know that when the syringe is fully depressed, but then the bung is added, the syringe plunger extends a bit. However in this experiment, the reaction won’t start straight away. Therefore I will need to make sure that I push the plunger back in before heat is applied. The experiment will be repeated 3 times and a mean of the results will be taken. All of the results must be concordant with the mean. This will reduce chance of any anomalous data being used. The condition must remain constant throughout each experiment. The collected gas should be at standard room temperature and pressure.
There is another test that could help find which equation is correct. In both equations CO2 is produced. To check this, we could bubble the gas through limewater, which turns milky in presence in CO2. However, in eqn1 O2 is also produced. The test for the presence of O2 is to place a glowing splint into the gas. If it relights, O2 is present. However, this method is not very adequate as the amount of O2 produced is very small in comparison to the CO2, and even if it was present it still might not affect a glowing splint
Providing under about 70cm3 of gas is produced, it shows that no oxygen is produced and so we can say that the 2nd equation is correct
During experiment, safety goggles should be worn throughout. Wear a lab coat so that it may be removed, without problem, if chemicals spill onto it. Plastic gloves should be worn to prevent chemical contact with skin. Also, when handling Bunsen burners, care should be taken.
Copper (I) oxide (Cu2O) – may be harmful if swallowed or if inhaled, could irritate lungs. If in contact with eye, rinse thoroughly with water for 15 mins and seek medical attention if problem persists. If in contact with skin, rinse with soap and water, and if swallowed in reasonable quantity, seek medical attention
Copper (II) Oxide (CuO) – Causes eye irritation, can damage cornea. Flush eyes with water for 15 mins. Irritates skin and can discolour it. If contact should occur, wash skin with soap and water. If swallowed, can cause damage to kidneys and liver. May also cause vascular collapse. However, do not induce vomiting, but drink cupfuls of milk. Id breathing is difficult do not give mouth to mouth resuscitation
Copper Carbonate (CuCO3) – risks are similar, yet not so hazardous. However treat with similar care. Do induce vomiting if swallowed
http://ptcl.chem.ox.ac.uk/~hmc/hsci/chemicals/copper_I_oxide.html – chemical safety on Copper (I) Oxide
http://avogadro.chem.iastate.edu/MSDS/CuO.htm – chemical safety on Copper (II) Oxide
http://en.wikipedia.org/wiki/Copper%28I%29_oxide – general information on the copper oxides
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