CuCO3 is a green powder and when it decomposes with heat, gas is released. I know after seeing a demonstration of the experiment that the CuCO3 changes colour for green to black when it has decomposed. In my research I found that copper oxide turns black when it has decomposed, but copper 2 oxide turns red. From this information I have an indication that copper carbonate produces copper oxide when heated.
To collect the gas I will use a gas syringe with a bung connected to the boiling tube. To make sure that just the gas is released from the boiling tube .I will put rock sill wool in the top of the boiling tube. The gas is made up from small enough particles that can pass through the wool, preventing the larger particles of the powder from entering the gas syringe and displacing the air.
I have seen the experiment and noticed that the CuCO3 started bubbling when it was heated. The bubbling is caused by gas escaping through the powder. The bubbling stops (the gas stops releasing) the reaction is over. From this observation I know to read the amount of gas given off after the bubbling has stopped.
When programming the experiment onto “Crocodile Chemistry”, I noticed that the syringe moved inwards when the reaction was over. This was because at the start of the experiment there is air in the delivery tube and boiling tube. When the air is heated it expands. After that apparatus cooled down the air then contracted. What was left in the gas syringe was the gas released from the reaction. I will leave the apparatus to cool down to room temperature before I read off the gas collected when doing the experiment.
I will need to know the volume of gas produced to ensure that it will be less than the maximum volume that the gas syringe can contain, so the volume can be read off.
Using my knowledge of moles I can calculate the amount of gas that will be produced for both equations. The calculated volumes will be compared with the actual amount of gas produced. The calculated volume of either equation that is the nearest to the amount collected in the experiment will be the correct equation for the reaction.
Here are my calculations
Equation 1
2½moles
CuCO3 (s) Cu2O(s) + 2 CO2 (g) + 1/2O2(g)
Mr = 247g 2½ × 24 = 60dm3
1g 60
= 0.24dm3/240 cm3
247
0.5g 60
= 0.12dm3/120 cm3
494
0.25g 60
= 0.06dm3/60.7 cm3
988
Equation 2
CuCO3 (s) CuO(s) + CO2(g)
Mr = 123.5g 1 × 24 = 24 dm3
1g 24
= 0.19 dm3/190 cm3
123.5
0.5g 24
= 0.095 dm3/95 cm3
247
0.25g 24
= 0.0475 dm3/47.5 cm3
494
Method
-
Set up apparatus as shown in the diagram, apart from the boiling tube with CuCO3
- Put on goggles
- Weigh boiling tube and record
-
Add CuCO3 powder into boiling tube on the scales until the additional weight of the powder weight the calculated amount
- Weigh the rock sill wool and record and place in boiling tube
- Attach boiling tube to clamp and set to an angle as illustrated on the diagram
- Place bung into boiling tube
- Make sure the valve on the Bunsen burner is fully opened
- Lit the Bunsen burner
-
Wait until the CuCO3 has stopped bubbling
- Turn Bunsen burner off
- Leave to cool to room temperature for about 5 minutes
- Read off volume of gas collected
-
Reweigh the boiling tube and contents and minus the weight of the boiling tube and rock sill wool to get the weight of the CuCO3
- Calculate the actual volume of gas produced to r.t.p. using the following equation:
P1 × V1 P2 × V2
=
T1 T2
Rearrange to give:
P1 V1
V2 = × T2
T1 P2
- repeat this whole method two more times and work out the average amount of gas collected
-
If he average volume of gas collected is near to 60.7 cm3, equation 1 is correct and if the volume of gas is nearer to 47.5cm3, equation 2 is correct.
