Thermal Decomposition of copper carbonate

It would also be important to consider the stability of CuCO3 with respect to both oxides, to see which reaction is energetically most likely. So it is clear that the value of ?Hf suggests that Cu2O will be formed, but that this will not necessarily be the case because of the other factors involved.

Copper (II) compounds are by far the most common - they are called "cupric". Copper (I) compounds - "cuprous" compounds are far less common. Copper atoms most readily go to oxidation state +2, by a variety of reactions. Cupric compounds are unstable in the presence of water, so must either be insoluble or form complexes with other molecules.

The equations are written in moles and through my background knowledge I now know the definition of a mole, '1mole of any substance contains the same number of particles as 12g of carbon-12. 1 mole of any element contains 6.01 x 1023 atoms. 1 mole of a molecular compound contains 6.01 x 1023 molecules'.

This means that in a reaction in which 2 molecules of one substance react with 1 molecule of another - for instance the formation of water: 2H2 + O2 ? 2H2O, 2 moles of hydrogen molecules will react with 1 mole of oxygen molecules to give 2 moles of water molecules. For an element, the mass of 1 mole is the same as the atomic mass in grams. For a compound the mass of one mole is the same as the relative formula mass or molecular mass in grams. The molecular or formula mass of a compound is found by adding the relative atomic masses of its constituent elements, as found in the periodic table.

Substance

Mr/Ar - and hence, mass of 1 mole (g)

Copper Carbonate (CuCO3)

23.5

Copper Oxide (Cu2O)

43

Copper Oxide (CuO)

79.5

Carbon Dioxide (CO2)

44

Oxygen (O2)

32

So using the equation of a reaction, it is possible to predict the masses of products that will be made by a given mass of reactants. In this experiment, from the two equations given, it is possible to calculate how much gas would be given off by each. Avogadro's law states that 1 mole of any gas occupies 24dm3 at room temperature and pressure (rtp), so it is possible to calculate the volume of gas given off. The experiment can then be carried out, and the volume of gas produced compared with the predictions for each equation. Whichever equation best predicts the volume given off is therefore shown to be the correct one.

Firstly I must deduce the amount of gases produced if 10g of copper carbonate is produced.

No. of moles = Mass s

Relative Molecular Mass

Relative Molecular mass of Copper Carbonate

=

Relative atomic mass of: Cu (63.5) + C (12) + O3 (16X3) = 123.5

No. of moles = 10

123.5

= 12.35

This is the number of moles for a solid and since I am trying to find volume of gas I must make the value relative to gases. Therefore I need to use reacting ratios.

Equation 1:

2CuCO3 (s) ® Cu2O (s) + 2CO2 (g) + 1/2 O2 (g)

CuCO3 : CO2 : O2

2 : 2 : 1/2

CuCO3 : Gases

2 : 2.5

1 : 1.25

No. of moles of gases = 1.25

No. of moles = 1.25 x 12.35 = 0.101

Volume = no. of moles x 24000 = 0.101 x 24000 = 2429

0g = 2429 cm³

g = 242.9 cm³

I scaled it down because the volumetric cylinder can only measure 500cm³.

Equation 2:

CuCO3 (s) ® CuO (s) + CO2 (g)

CuCO3: CO2

1 : 1

No. of moles of CuCO3 : No. of moles of CO2

Volume of gas = no of moles x 24000

= 0.0801 x 24 = 1944 cm³

0g = 1944 cm³

g = 194.4 cm³

I have decided to carry out this experiment using a volumetric cylinder. Although the gas syringe and gas measuring tube are more accurate. In this experiment in order for me to use them I would have to scale the mass down to less then 1g and this will increase the chance of error both at weighing and when reading of the values. Therefore it is more accurate to use the volumetric cylinder because after having done my calculations I realized that in the results there would be a 50 cm3 difference between the two values.

Apparatus

. Heat proof mat

2. Bunsen burner

3. Boiling tube

4. Bung

5. Gas delivery tube

6. Gas syringe

7. Top balance scale

8. 1g of copper carbonate

9. Safety goggles

0. Laboratory coat

1. Measuring boat

Method

. First weigh 1g of copper carbonate in the measuring boat on the top balance scale. Then weigh the measuring boat on its own. Take away the weight of the measuring boat from the copper carbonate and record the values in table 1

2. Set up the apparatus as shown

3. Place the weighed quantity of copper carbonate in a test tube and insert a bung tightly to ensure that it is air tight and gas loss is kept to an absolute minimum. This also guarantees that the results obtained are accurate

4. Light Bunsen burner and place under tube.

5. Wait until the copper carbonate has completely decomposed. This will be indicated by a color change, and the fact that the copper carbonate would have stopped bubbling. Copper carbonate is a green solid. Copper oxide is a jet black solid.

Green Black

6. When you are sure the copper carbonate has completely decomposed, measure and note down the volume of gas obtained

7. Repeat stages 1 - 6 three to four times, and then take the average.

This reduces the risk of error in your results. Also ensure that all variables capable of influencing the results are kept constant.

For example, the same amount of copper carbonate is used in each experiment and using the same apparatus again helps reduce the risk of error

Results

Table 1

Measurement of boat

Measurement of boat and Copper Carbonate

Measurement of boat after

Final measurement

Table 2

Measurement of copper carbonate used g

Volume of Gases produced cm³

In this experiment if the volume produced is nearer to 242.9 cm³ then It will mean that equation 1 is correct. If the volume of gases produced is nearer to 194.4 cm³ then equation 2 is correct. I predict that the most probable equation that is correct is equation 2. Previous knowledge may also help to support this prediction as when anything combusts oxygen gas is never given off as a product because the oxygen is needed for the reaction.

#

References

http://www.chemistry-react.org/go/Tutorial/Tutorial_4642.html

L. Ryan (2000). Advanced Chemistry for You: Page 117

E.N RAMSDEN (2000). A Level Chemistry 4th Edition -: Page 151-6

B. Ratcliff (2000) .editor. Chemistry 1: page 26-27

http://science.widener.edu/svb/tutorial/avogadroslaw.html

Sarah. Y. Kargbo

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