Calculation
RMM (relative molecular mass) of copper carbonate (CuCo3) =64 +12+ (16×3)
As we also know that ‘At room temperature and pressure (r.t.p), 298K (25。C) and 100kPa, 1 mole of any gas will occupy 24dm³ or 24000cm³’
Therefore if 1 mole is 24000cm³ V= n × 24000
∴ 1 mole is 24000cm³ then 1/24000 is 1cm³
The compound copper carbonate, CuCO3 decomposes on heating to form one of these oxides and two equations provided for possible reaction are:
Expressing equation (1) chemical reaction in terms of 1 mole we get:
CuCO3 (s) → ½ Cu2O (s) + CO2 (g) + ¼O (g)
Decomposing 1 mole of Copper carbonate will produce half a mole of copper oxide (solid), 1 mole of carbon dioxide (gas) and ¼ oxygen (gas) are formed.
Both carbon dioxide and oxygen gases are collected together; therefore the total volume of gas produced is 1.25 moles.
Equation 2 chemical reaction in terms of 1 mole we in fact get:
CuCO3 (s) → CuO (s) + CO2 (g)
1 mole of Copper carbonate will produce 1 mole of copper oxide and one mole of carbon dioxide gas is produced.
Using this equation I can calculate the mass of 1 mole copper carbonate.
M = Number of moles of substance.
m = Mass in grams
Mr = Mass of 1 mole in grams
1= m ÷ 123.5
∴ Mass of 1 mole of CuCO3 = 123.5 g
Equation 1
Volume = Moles × 24 000cm3
= 1.25 × 24 000
= 30 000 cm3
30 000 will be produce by 1.25 moles of Copper carbonate.
Equation 2
Volume = Moles × 24 000cm3
= 1 × 24 000
= 24 000cm3
In this experiment the volume of gas formed will be collected using an apparatus with the maximum capacity of 100cm3. Because when the gas is at a high temperature it expands, to avoid any errors, I will only collect maximum 75cm3of gas.
123.5 CuCO3 = 30 000cm3
Mass = Mr ÷ Volume in cm³ × 75
CuCO3 = (123.5 ÷ 30) × 75 = 0.30875g
= 0.3 (1 d.p)
∴Mass of CuCO3 that would develop 75cm3 of gas in equation 1 = 0.3g
Now by using the same mass, I can find the volume of gas will be produced by equation 2
123.5 CuCO3 = 24 000cm3
1 CuCO3 = 24 ÷ 123.5
Volume of gas = (24 ÷ Mr) × Mass
Volume of gas = 24 ÷ 123.5 × 0.3
= 60 cm3
∴ Using the same mass of CuCO3 volume of gas that would evolve by equation (2) = 60cm³.
3
Fair Testing
The condition must ensure a fair test, certain variables must be maintained, the main variable that has to be kept the same is temperature, the collected gas should be kept at room temperature, and the gas syringe should be kept as far away as possible when heating the copper carbonate. The gas syringe should be cooled down for a short period of time after the copper carbonated has been heated. This is because gas at a higher temperature expands and so occupies a larger area than corresponding cooler gas. All the copper oxide must decompose before the heating is stopped (the colour change from blue to black). The bung must e tightly inserted to reduce gas loss. Make sure you measure the amount of copper carbonate properly because 0.01g can make change the whole result of the experiment. And I need to repeat the experiment 3 times an
Safety
Basic carbonate is harmful if swallowed. The dust will also irritate the lungs, skin and eyes. This means that when conducting the experiment we will wear goggles and a lab coat. If it gets on our skin we are to wash the area thoroughly. Wash contaminated clothing before reuse.
When dealing with the Bunsen burner we must also take care not to burn ourselves, by either touching the burner while hot or touching and of the equipment it has heated.
Equipment
Heat proof mat
To protect the work surface from the heat or fire produced by the Bunsen burner.
Bunsen burner
Provide heat and fire to heat up the copper carbonate for the thermal decomposition.
Splint
To light the Bunsen burner
Spatula
Carry the Copper carbonate from the container to weighting scaled, then to the boiling tube.
Boiling Tube
Container for copper carbonated and boiling tube can withstand high amounts of heat and will contain CuCO3.
Bung
To seal the boiling tube and make sure the boiling tube is an airtight seal. Unlike a lid which encloses a boiling tube from the outside without displacing the inner volume. Digital weighting scales to weight copper carbonate to great accuracy.
Delivery Tube
Transfer the gas from the boiling tube, to the graduated cylinder/gas syringe.
2 Claw Clamp, 2Retort Stand
To hold the boiling tube on the retort stand, it holds the boiling tube up while the Bunsen burner is burning the boiling tube and one to hold the gas syringe in.
Digital Scales
Weight the copper carbonate and have an accurate reading to 1 decimal point.
Safety goggles
Copper carbonate is irritant to the eye and need goggles to prevent that the copper carbonate to have any contact with the eye.
Laboratory Coat and Rubber gloves
Prevent the copper carbonate to absorb through skin.
Graduated cylinder (only use it in method 1)
It collects the gas from the boiling tube to the graduated cylinder through the delivery tube.
Water bath (only use it in method 1)
For the graduated cylinder to sit in.
Gas syringe (only use it in method 2)
It measures the volume of the gas. The syringe will seal around the top and sides and you can move the syringe more freely then the Graduated cylinder
Note: When using a gas syringe you must not get it wet. Dry off the inside tube with a paper towel, so that the movement of the syringe is smoother and more reliable when gasses are being measured.
Desiccator
This is a sealable enclosures containing preserving moisture-sensitive to the copper carbonate. When the desiccator is exposed to the atmosphere, I need to quickly measure the mass and do the experiment as quickly as possible for the less moisture to be in the copper carbonate. I need to put the copper carbonate inside the desiccator a week before the experiment, to make sure the least amount of moisture inside the copper carbonate as possible.
Make sure that the gas syringe is at 0 before beginning the experiment.
Prediction
By carrying out the experiment and determining the total volume of gas 1 collected is 60cm³ or 75cm³. if I collected 60cm³ know it is equation 1 and if I collected 75cm³ I know it is equation 2.
But it might not be exact becuast it is only 5cm apart and I will be doing int a school laboratory, therefore I wll need to look at the colour change to determining which equation is the right one. Equationg 1 and 2 both form a solid copper oxide, but they have a different physical properties to one another. If it is Copper I (equation 1) then the copper carbonate will form Cu2O, cuprous oxide and turn red. However, if the Copper II (equation 2) then the copper carbonate will form Cu2 cupri oxide and it will turn black.
It will be much easier to tell it through colour then the volume of gas, even through I try not to have any kind of gas escaping and make sure the copper carbonate is the right mass.
Method 1
- Connect the retort stand and the claw clam together
- Used a digital scale and measure 0.4g.
- Put 0.4g of copper carbonate into a boiling tube; replace the bung in the boiling tube ensuring an airtight seal and put the boiling tube inside the claw clam.
- Fill a100ml graduated cylinder with water to the top, cover, invert, lower into a filled trough, and fill the trough with water.
- Attach the delivery tube to the bung and position the graduated tube over the end of the delivery tube.
- Heat the copper carbonated slowly with a laboratory Bunsen burner.
- Bubbles will collect in the graduated cylinder, Measure the volume when all the copper carbonate has all reacted, when the entire copper carbonate change colour, then all of your copper carbonate has reacted.
Remove the gas delivery tube from under the water as soon as bubbling stop. If not, as the gases cool, water may be sucked back into the tube and the delivery tube at the same time.
This method is not so good because the gas can easily escaped. This experiment has to be accurate but this method tends to be heavy loss of gas evolved.
Method 2
(Do 1 to 3)
4. Attach the delivery tube to the gas syringe and the bung with the boiling tube. Make sure the bung, to prevent any gas escaping into the outside atmosphere.
5. Heat the copper carbonated slowly with a laboratory Bunsen burner.
6. Connect the retort stand and the claw clam together and put the gas syringe inside the clam.
7. Heat the copper carbonated slowly with a laboratory Bunsen burner.
8. When of all copper carbonate change colour, you know it is all reacted, then you way for your gas to cool down.
9 Wait 20 minute before taking a result while the copper oxide cools and all the gas has been released while the copper carbonate decomposes. Wait till the gas in the gas syringe cool down to room temperature before I take a reading because I will be certain that the gas is in room temperature with 24dm gases in one mole.
Additional
These tests can also prove which equation is correct.
Lime water –inject some gas into a boiling tube fill with lime water with the gas syringe and if the lime water turn milky, then carbon dioxide is present.
Splint test – inject some gas into a boiling tube and put a glowing splint in it, and if the splint glows even more then a oxygen is presence then equation 1 would be right.
Reference
“Letts Chemistry – Revise As” By Rob Ritchie” pages 33 – 36.
“Essential As Chemistry of OCR” By Ted Lister and Janet Renshaw.