The compound copper carbonate, CuCO3 decomposes on heating to form one of these oxides and two equations provided for possible reaction are:
Equation (1): 2CuCO3 (s) → Cu2O (s) + 2CO2 (g) + ½O (g)
Equation (2): CuCO3 (s) → CuO (s) + CO2 (g)
Expressing equation (1) chemical reaction in terms of 1 mole we get:
CuCO3 (s) → ½ Cu2O (s) + CO2 (g) + ¼O (g)
This tells us that by decomposing one mole of CuCO3, half a mole of copper oxide, one mole of carbon dioxide gas and a quarter mole of oxygen gas are produced. Since both carbon dioxide and oxygen gases are collected together, the total volume of gas produced is 1.25 moles.
Expressing equation (2) chemical reaction in terms of 1 mole we in fact get:
CuCO3 (s) → CuO (s) + CO2 (g)
So, by decomposing one mole of CuCO3, one mole of copper oxide and one mole of carbon dioxide gas are produced.
To produce one mole of gas by either of the equation the mass of one mole of CuCO3 can be calculated. This can be done using the formula M = m / Mr, where ‘M’ is the number of moles of substance; ‘m’ is the mass in grams; and ‘Mr’ is mass of 1 mole in grams
∴ Mass of 1 mole of CuCO3 = 123.5 g
At room temperature and pressure 1 mole of any gas is 24.0dm3 (1000cm3 = 1dm3)
Volume of gas produced by decomposition reactions in equation (1) and (2) are, as follows:
Equation (1)
Volume = Moles × 24.0dm3
= 1.25 × 24.0
= 30.0 dm3
Equation (2)
Volume = Moles × 24.0dm3
= 1 × 24.0
= 24.0 dm3
In my experiment the volume of gas produced will be collected using an apparatus with maximum capacity of 100cm3. To avoid any large errors whilst conducting the experiment I intend to collect the maximum volume of gas as 75cm3. Using reaction in equation (1) I am able to find the mass of CuCO3 in grams that would produce the maximum gas volume of 75cm3.
123.5 CuCO3 → 30dm3
75cm3 → 0.075 dm3
Mass =
Mass of CuCO3 =
= 0.30875g
= 0.3g (1d.p.)
∴Mass of CuCO3 that would evolve 75cm3 of gas in equation (1) = 0.3g
Now by using the same mass, 0.3g I can find the volume of gas produced by equation (2).
123.5 CuCO3 → 24.0dm3
1 CuCO3 →
Volume of gas =
Volume of gas =
= 60 cm3
∴ Using the same mass of CuCO3 volume of gas that would evolve by equation (2) = 60cm3.
Prediction:
I predict
By carrying out the experiment and determining whether total volume of gas collected is 60cm3 or 75cm3 I can determine which of the two reactions equations is correct.
The metal copper comes from the colorant family. Both equation (1) and (2) form a solid copper oxide, but have very different physical and chemical properties to one another. After decomposing the copper oxide formed in equation (1), ‘ Cu2O’ has an assigned chemical name, cuprous oxide and is brick red in colour. However, the copper oxide formed in equation (2), ‘CuO’ is known as cupric oxide and is black in colour.
Hence, I can further predict:
If the solid copper oxide appears to be brick red in colour then equation (1) is correct. However, if the copper oxide is black in colour equation (2) is correct.
Apparatus:
To collect the gas I could either use a 100cm3 cylinder upside down in a water bath or 100cm3 gas syringe. The following two diagrams show the layout of the two apparatus:
Fig 4 Fig 5
Measuring Cylinder Gas Syringe
Carbon dioxide is heavy and soluble in water when under pressure this means that using a measuring cylinder upside down in a water bath will not give an accurate reading of CO2. This is because a percentage of CO2 will be dissolved forming, H+ ion and HCO3- ion. Due to this I shall use a gas syringe to collect the gas produced during thermal decomposition for copper carbonate.
A 100cm3 gas syringe ±1cm3 – To collect gas produced during thermal decomposition for copper carbonate.
Dessicator – To absorb water vapour from CuCO3 preventing water vapour from turning in to gas as well as removing extra mass of CuCO3 added by water vapour.
Digital weighing scale ± 0.1g – To weigh the reactant and the product produced with an accurate reading to 1 decimal point.
Bunsen burner– To provide heat for thermal decomposition.
3 Boiling tube – Boiling tubes can withstand high amounts of heat and will contain CuCO3. I will need 3 boiling tubes to conduct repeat tests so as to get the most accurate readings.
1 Retort stand – To raise the boiling tube above the bunsen burner.
Claw Clamp – To hold the boiling tube above the bunsen burner
Boss Head – To connect clamp to retort stand.
CuCO3, powdered form – The reactant to undergo thermal decomposition.
Bung – To prevent unwanted air to interfere with the thermal decomposition reaction.
Plastic delivering tube – To transport the gas produced during the thermal decomposition reaction, as the tube is plastic, it has greater flexibility so as to be easily arranged when setting up experiment.
Heat/ fire resistant matt – To make sure work surface does not get damaged by the heat or fire produced by the bunsen burner.
Safety goggles – CuCO3 is irritant to the eyes therefore goggles are needed to prevent any contact with the eye.
Spatula – To transport CuCO3 from container to weighing scale and then to boiling tube.
Plastic Gloves – To prevent skin contact with copper carbonate as copper carbonate is harmful.
Diagram:
Fig 6
Method:
- Connect the retort stand to the claw clamp using a boss.
- Place retort stand above a heat resistant matt.
-
Using a digital weighing scale measure 0.3 ± 0.1 grams of CuCO3.
-
Place the weighed CuCO3 into the dessicator
-
Place the weighed CuCO3 into a boiling tube.
-
Taking the boiling tube containing the CuCO3 from the rack connect it safely in between claw clamp. Making sure to screw the boiling tube between the boss tightly , thus preventing the boiling tube from falling and breaking.
- Insert the bung, which has a connected delivery tube, into the boiling tube.
- After doing so, connect the free end of the delivering tube to the gas syringe. Again make sure that the delivery tube is connected to the gas syringe tightly. Thus preventing any gas from escaping into the outside atmosphere, which could ruin the experiment.
- Light the bunsen burner and set the bunsen burner to a strong blue flame.
-
Place bunsen burner under the CuCO3 contained in the boiling tube.
-
Continue to heat the CuCO3 until all visible CuCO3 has changed colour from green to red or black
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When CuCO3 has changed colour, turn the gas tap off so as to turn off bunsen burner.
-
Let the gas within the gas syringe cool so as to get accurate measurement of gas as gas expands when heated and make sure volume of gas collected is approximately either 60cm3 or 75cm3.
- Record results of experiment, this being colour of copper oxide and volume of gas collected.
Safety Procedures:
When handling with any chemicals or carrying experiment wear safety goggles and plastic gloves. All spillage should be cleaned up immediately.
First Aid measures:
Skin Contact = Any chemical which has come in contact with the skin, that area has to be washed immediately with large quantities of running water. If irritation continues seek medical attention.
Eye Contact = For at least five minutes wash the eyes with water or a saline solution. If irritation continues seek medical attention.
Ingestion = If chemical has been taken in the mouth, you must wash mouth with large amounts of water. If the chemical enters into the stomach, then give 250cm of water to dilute the chemical in the stomach. In more serious cases obtain medical attention.
Reference:
"Essential A2 Chemistry for OCR" By Ted Lister and Janet Renshaw 2004, Publisher: Nelson Thornes
Pages: 86-87
"Essential AS Chemistry for OCR" By Ted Lister and Janet Renshaw 2004, Publisher: Nelson Thornes
Pages: 26-27
“Chemistry 1 - Advanced Sciences” By Brian Ratcliff, Helen Eccles, David Johnson, John Nicholson, John Raffan 2000, Publisher: Cambridge
Pages: 206, 179
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Fig 2:
Fig 3:
