# decomposition of copper carbonate

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) + ½ 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 cm³) 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) ---------------------> CuO (s) + CO2 (g)

'1 mole of copper carbonate will decompose to 1 mole of CuO and 1 mole of CO2'

'1 mole of gas occupies 24360 cm³ at 20°C, 100kPa'.

I aim at 30 cm³ volume of gas, so I can ensure all gas is measured.

Thus, if 1 mole of copper carbonate produces 24360 cm³ of CO2, to produce 30 cm³ we need:

• number of moles    = volume cm³/24360  cm³

=   30 cm³       /24360  cm³

= 0.0012315271 moles of gas

• Mr of CuCO3    = 63.5+12+(3*16)= 123.5

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