The decomposition of copper carbonate - proving one of two equationsAim

Table of data on Substances involved in reaction

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 our 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.

Risk Assessment

During the practical there are several potential hazards involved therefore I will obide by all of the usual lab rules;

• I will wear a lab coat and goggles
• I will tie my hair back to avoid accidents and distractions
• I will clear the lab by putting stools under desks
• I will behave sensibly (i.e. no running)

In addition there are several safety measures specific to the chemicals we are using/producing in our investigation, I had to ensure I was aware of these prior to the practical.

 

Hazcards

26. Copper Oxides, carbonates and sulphides

Basic Copper Carbonate (Malachite) HARMFUL –

• Harmful if swallowed.
• Dust irritates lungs and eyes

Copper (l) and Copper (11) Oxide HARMFUL –

• Harmful if swallowed.
• Dust irritates lungs and eyes.
• DANGEROUS WITH: Aluminium and Magnesium (explosive materials are formed)

20. Carbon Dioxide

Large quantities of the gas can asphyxiate

If rooms are not ventilated while natural gas is being burnt in bunsen burners, there is a rise in the concentration of carbon dioxide and carbon monoxide and a loss of oxygen

69. Oxygen

 Contact with combustible material may cause fire. Combustible substances burn much more fiercely in even slightly oxygen enriched air. This is unlikely to be a risk on a large scale, even if a cylinder leak occurs, but be aware of the risk in any investigation where oxygen is used in enclosed apparatus.

Diagram of apparatus

Apparatus

- Top pan balance - The top pan balance is accurate to 0.005g. For a mass of 0.15g, this is accuracy to within 3.0% (0.005/0.15 x 100)

- Boiling tube and bung - a tight-fitting bung will ensure that no gas is lost once heating has started.

- Gas burette - a burette is accurate to 0.05cm3. For a 25cm3 volume, this is accuracy to within 0.2%. The experiment needs to show which of the two equations is correct, and the volume of gas produced by each differs by just approximately 21.5cm3, so an inaccuracy of 0.05cm3 will still allow which reaction is taking place to be clearly discerned.

-Spatula – To allow for the safe handling of the CuCO3 

- Bunsen burner – used to heat test tube

- 2 Bosses, clamps and clamp stands – used for securing the boiling tube and gas burette

- Trough and delivery tube and funnel - The two gases which could possibly be produced are oxygen and carbon dioxide. Both are only sparingly soluble at room temperature and pressure and so are suitable for being collected over water, using this apparatus.

Total quantifiable inaccuracy is approximately 3.4% (3.2+0.2), which is an acceptable value and should not distort my results.

Method

1. Set up the apparatus as shown in the diagram, place the boiling tube into the clamp stand, ensuring that the bung is firmly in place and the clamp is holding the boiling tube as close to the bung end as possible to avoid setting the cork on the clamp alight with the Bunsen burner
2. Heat an empty boiling tube (in order to calculate the volume of air produced on expansion). This is known as a "control" experiment, in which no copper carbonate is used, but an empty boiling tube is heated for the same length of time, and the volume of the gas collected due to expansion of the air measured. This volume can then be subtracted from the volume obtained by the decomposition of the copper carbonate to give a more accurate result for the volume of gas given off
3. Weigh out 0.15g of CuCO3 as accurately as possible using the balance
4. Place the CuCO3 half way along the clean boiling tube carefully, using a spatula.
5. Heat the CuCO3vigorously until all the green powder has turned black, and no more gas is being produced.
6. Stop heating, and immediately remove the delivery tube from the trough by lifting the clamp stand holding the boiling tube and moving everything clear of the water to prevent suck back.
7. Take the final reading from the gas burette, and calculate the total volume of gas given off.
8. Repeat this procedure three times using a different boiling tube each time as well as resetting the gas syringe. Doing this will enable me to take and average of all replicates and therefore discount any anomalous results and thus improve the reliability of my results.
9. Work out an average figure of gas given off from the 5 experiments
10. From this it should be possible to calculate which equation is correct by the amount of gas produced

There are certain conditions that must remain constant for the experiment to be fair. These are represented in the table below:

Conclusion:

When an average has been obtained we should be able to see which of the equations is correct. If the amount of gas released is approximately 40cm3 as predicted for equation 1, this would indicate that equation 1 is correct. If the average is lower (by approximately half the volume produce by equation 1, i.e. 18.5cm3) this would indicate that less gas has been produced, and thus suggest equation 2 is correct.

The most probable equation to be proved correct is equation 2 because as Oxygen is needed for the reaction and the products are oxides, Oxygen cannot itself be released during combustion reactions, as indicated in the 'Oxford Dictionary of Chemistry'. Oxygen cannot be produced as a product, therefore we can disprove equation 1.