Which Equation is Correct?

Carbon dioxide

Carbon (IV) oxide, it has a concentration of 0.033% of the atmosphere. It can be tested for by bubbling it through limewater, the limewater will turn milky.

The mole

A mole is defined as the quantity of a substance that has the same number of particles as are found in 12.000 grams of carbon-12. This number, Avogadro's number, is 6.022x1023. The mass in grams of one mole of a compound is equal to the molecular weight of the compound in atomic mass units. One mole of a compound contains 6.022x1023 molecules of the compound. One mole of gas at room temperature (25°C) and pressure (1 atm) occupies a volume of 24dm3

Endothermic reaction

The reaction involved is an endothermic one, energy is taken in to break down the copper carbonate, the energy content of the products is higher than that of the reactants as heat is taken in by the system.

Diagram of an endothermic reaction

Fair Testing

The conditions 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, 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 carbonate has been heated. This is because gas at a higher temperature expands and so occupies a larger area than corresponding cooler gas. The gas syringe must be a 0 before the experiment is started. All the copper oxide must decompose before the heating is stopped (the colour has changed completely). The bung must be tightly inserted to reduce gas loss. The test will be repeated until there are 3 consistent results to obtain a good average, this would minimise the chance of anomalous results. The apparatus must be kept the same and cleaned properly throughout the tests.

Enough copper carbonate should be used so that the gas produced is less than the volume of the gas syringe so it can be measured. However, there must be enough gas produced so that the result is accurate.

Safety

When conducting the experiment goggles and a lab coat have to be worn, the copper carbonate dust may irritate the eyes, etc. Care must be taken in using a Bunsen burner.

Method of the practical

Apparatus

Bunsen burner - to heat copper carbonate

Splint - to light Bunsen burner

Heatproof mat -protection against heat

Boss and clamp stand - to hold gas syringe

00cm3 (0.1dm3) syringe - to measure volume of gas produced

Boiling tube - container for copper carbonate to be heated, has a higher surface area to heat the copper carbonate than a conical flask

Test tube holder - to hold boiling tube

Tube with bung attachment - so gas can pass from conical flask to gas syringe with minimal loss

Accurate balance - to weigh copper carbonate to great accuracy

Chemicals

0.24 grams of copper carbonate

Limewater

Safety

Safety goggles

Lab coat

I have chosen to use 0.4g of copper carbonate because the amount of gas I predict it to produce is a reasonable amount less than the maximum measuring capacity of the gas syringe.

Calculations

Moles = Mass/RMM

RAM (relative atomic mass) of

Cu = 64 C = 12 O = 16

Therefore:

RMM (relative molecular mass) of copper carbonate (CuCO3) = 64 + 12 + (16 x 3)

Therefore:

Moles = 0.4/124

= 0.0032258064516129032258064516129032

With either formula, the ratio of CuCO3 to CO2 is 1:1 so the number of moles of CO2 is the same as for CuCO3.. 1 mole of CuCO3 will decompose to give you 1 mole of CuO and 1 mole of CO2, it is a stoichyometric equation.

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

1 : 1

Equation 2: CuCO3(s) CuO(s) + CO2(g)

1 : 1

Volume of gas (carbon dioxide) produced = moles x 24000

= 0.0032258064516129032258064516129032 x 24000

˜ 77.4cm3

Using 0.4g of copper carbonate, I have calculated hat 61.9cm3 of carbon dioxide will be produced, that is a small enough volume to be measured by the gas syringe that is going to be used and large enough for the measuring to be accurate. If equation 1 is correct and oxygen is produced, there is enough space left for that. If there is a substantial amount of gas more than 77.4cm3 then there is oxygen produced from the reaction as well meaning the first equation is correct

Method

. Set up equipment as shown in diagram

2. Weigh (0.4 grams) of copper carbonate.

3. Place the copper carbonate into a boiling tube and insert a bung with tube attachment tightly to ensure that it is air tight and gas loss is kept to a minimum to ensure accuracy

4. Use test-tube holders to hold boiling tube with copper carbonate above a Bunsen burner on full power

5. When copper carbonate has gone completely black (completely decomposed) and bubbling has stopped

6. Wait for the gas syringe to cool down before measuring and noting down the volume of gas obtained.

7. Repeat to get 3 consistent results and 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.

Diagram of apparatus set-up

I shall first calculate the gas that would be collected by both equations and then talk about the method used to decompose the copper carbonate and collect the gas. Then I will explain how you would compare the actual gas collected to your to two theoretical values of gas produced and thus find out the correct equation.

Other tests

Limewater could be used to make sure that carbon dioxide is produced: it turns milky in presence of carbon dioxide; this is to make sure that one of the equations is possible

A glowing splint could be used to test whether oxygen is produced: it re-lights in presence of oxygen, if it is shown that oxygen is released, then equation 1 is correct.

Conclusion

If the amount of gas produced matches or is slightly less than the predicted amount, this shows that carbon dioxide and no oxygen is produced, proving equation 2 to be correct. Collecting slightly less gas in the syringe shows that escape of gas. Therefore I predict that equation 2 is correct. In addition, in combustion reactions, oxygen is needed for the reaction so it is never produced.

References

ga.gov.au/education

digitalfire.com

Chemistry in Context