I will do this by decomposing the copper carbonate. I will need to calculate if the volume of carbon dioxide produced is equal to what the equation suggests.
Equipment:
- Heatproof mat
- Bunsen burner
- Boiling tube
- Bung
- Delivery tube
- Water bath
- Measuring cylinder (250 cm³)
- Digital weighing scales
- Spatula
- Clamp and stand
- One molar copper carbonate (1 gram)
- Two molar copper carbonate (1 gram)
Safety and accuracy:
- Copper carbonate is harmful if swallowed and can irritate the lungs and eyes. Ensure that goggles and a lab coat are worn during the experiment.
- Ensure that all the copper carbonate has been fully decomposed. The colour will change from green to black (copper oxide).
- Wait 5-10 minutes before measuring the volume of carbon dioxide produced as this will allow it to cool down to room temperature
- Repeat the experiment to obtain another set of results.
- The apparatus used should be totally air tight so no gas can escape.
- Try to make sure that there are no bubbles of gas in the measuring cylinder full of water before starting the experiment.
- Always measure from the bottom of the meniscus.
Calculations and method:
Using the first equation:
2CuCO3 (s) Cu2O (s) + 2CO2 (g) + ½ O2 (g)
Molar ratio: 2 1 + 2 + ½
Using 1 gram of copper carbonate:
Number of moles = Mass / Mr
= 1 / 123.5
= 8.097 x 10³ moles copper carbonate
Because the molar ratio between the copper carbonate and the gas is 2 : 2 ½, the number of moles of gas produced = 8.097 x 10³ moles x 1.25
= 1.012 x 104 moles
Volume of gas produced = number of moles x 24 dm³
= (1.012 x 104) x 24
= 2.429 x 105 dm³ (242.91 cm³)
Therefore, if 1 gram of 2 molar copper carbonate is to be used, approximately 242.91 cm³ of gas should be produced.
Using the second equation:
CuCO3 (s) CuO (s) + CO2 (g)
Molar ratio: 1 1 + 1
Using 1 gram of copper carbonate:
Number of moles = Mass / Mr
= 1 / 123.5
= 8.097 x 10³ moles copper carbonate
Because the molar ratio between the copper carbonate and the gas is 1 : 1, the number of moles of carbon dioxide = 8.097 x 10³ moles.
Volume of carbon dioxide produced = number of moles x 24 dm³
= (8.097 x 10³) x 24
= 0.19433 dm³ (194.33 cm³)
Therefore, if 1 gram of 1 molar copper carbonate is to be used, approximately 194.33 cm³ of gas should be produced.
Method:
- Collect all the apparatus required and rinse out the glassware with water.
- Set up the apparatus as shown in the diagram below:
- Using the second equation to help with the theory, weigh out 1 gram of one molar copper carbonate accurately using a spatula.
- Transfer the 1 gram of copper carbonate into a boiling tube and insert the bung tightly to ensure there are no air gaps.
- Fix the boiling tube into the clamp and make sure that the delivery tube is directly underneath the measuring cylinder.
- Heat the copper carbonate until it has turned black in colour and the volume of gas in the measuring cylinder has stopped moving.
- Measure and note down the volume of gas produced.
- Repeat the procedure to get another set of results.
- Repeat the entire experiment but replace the 1 molar copper carbonate with 2 molar copper carbonate and record the volume of gas produced.
(I could have used a gas syringe instead of the upturned measuring cylinder in a water bath. This would have been a lot more accurate. However, I am not experienced with using a gas syringe and accuracy is not entirely essential in this experiment as the volumes of gas that are expected to be obtained have a large difference between them therefore allowing room for error.)
After carrying out the experiment I can compare the volumes of gas given off from using different molars of copper carbonate and therefore decide which equation is correct.
If the water displaced/gas given off is around 243 cm³ it is going to be the first equation which is correct:
2CuCO3 (s) CuO (s) + 2CO2 (g) + 1/2O2 (g)
If the amount of gas produced is around 194 cm³ it is the second equation that is correct:
CuCO3 (s) CuO (s) + CO2 (g)
Bibliography:
http://www.chemistry-react.org/go/Tutorial/Tutorial_4642
www.wmblythe.co.uk/WMBLYTHE/CSDS.nsf/0/dbda27f956dd7415802566c0004ee74e?
AS-Level Chemistry Revision Guide pages 12-13 and 16-17
Chemistry 1 pages 26-27
