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decomposition of copper carbonate

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Introduction

Chemistry Coursework Skill P: Decomposition of copper carbonate This is an experiment to determine the thermal decomposition of copper carbonate. As seen in equation 1 and 2 Cu2O and CuO are possible outcomes. Equation 1: 2 CuCO3 (s) -------------------------> Cu2O (s) + 2 CO2 (g) + 1/2 O2 (g) Equation 2: CuCO3 (s) --------------------------> CuO (s) + CO2 (g) By performing a quantitative analysis of the gas volume the two equations can be distinguished. Background theory Copper carbonate is found in nature as the mineral malachite and is a green powder. When heated it decomposes to give black copper oxide (CuO) and carbon dioxid. The melting point is 260 �C. Copper has two different oxides, CuO and Cu2O. CuO transfers at 900 �C into Cu2O with loss of oxygen (Hollemann - Wiberg). Thus for this experiment I expect equation 2 to be correct. Calculating the correct mass of copper carbonate To receive an adequate amount of gas volume(maximum volume of burette: 50 cm�) I first have to calculate the necessary amount of CuCO3: With a molar ratio of 1:1 I use Equation two to calculate the necessary mass of copper carbonate Equation 2: CuCO3 (s) ...read more.

Middle

after ending of reaction to measure gas evolved * ensure that there are no air bubbles in the burette * perform experiment accordingly without CuCO3 and measure collected gas. This volume is to be deducted from the actual results (temperature effect) * ensure that all copper carbonate has been fully decomposed (colour change) * precise reading for temperature and air pressure Variables controlled variables: * the pressure of the room, to measure with a barometer for the final calculation. * the temperature. An increase in temperature may cause an increase in the volume of gas given out by the expansion of the air. * degree of decomposition of copper carbonate. The green copper carbonate has to turn black completely and has to be heated evenly(heating time). * Dependent variable: * amount of gas. * Independent variable * copper carbonate - fixed Risk assessment * copper carbonate is toxic and it can irritate lungs and eyes * copper(1)oxide is harmful if swallowed and can irritate lungs and eyes * carbon dioxide has a low hazard symbol. It is asphyxiate and lowers the oxygen content of the air. ...read more.

Conclusion

(2 d.p.) 12 repeat experiment three times 13 work out average volume of gas evolved The volume of gas is temperature and pressure dependent. Therefore you have to use a barometer (not available at school) and a thermometer to calculate the correct volume. I reduce the temperature effect of the heated gas by waiting 10 minutes before measuring it. General gas equation P*V= n*R*T P= Pressure V= Volume n=moles of gas R= gas constant =8.314 J k?' mol?' T= temperature Example calculation: P*V=n*R*T V= (n*R*T)/P = (1 mol*8.314J k?' mol?' *293 kelvin)/100kPa = 24.36 dm� at 20 �C and 100kPa pressure After calculating an average volume of gas produced you can compare this with the theoretical results of 30 cm� for equation two and 37.5 cm� for equation one. As mentioned above I predict equation 2 to be correct, thus 30 cm�, or closest to this, of gas should be measured. Due to the small amount of reactants already small deviations in measurement of weight, temperature and pressure could, when added up, show a certain margin of error. Thus more accurate tools (e.g. analytical balance), increased mass of reactants and standardized heating will improve accuracy of results. Alternatively use gravimetric measurement of CuCO3 and CuO respectively. ...read more.

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