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Copper is a red-brown metal. When it is heated in air, it turns black because it combines with Oxygen to form Copper (ii) oxide.
Copper + Oxygen = Copper (ii) oxide
(Red-brown) (colorless) (black solid)
( solid ) ( gas )
Volume of air in syringe A before heating = (7.5cm)^3
Volume of air in syringe A after heating =(6.0 cm)^3
Volume of air used up during heating =(1.5cm)^3
% of air used up during heating = (Volume of air used during heating )/(original volume of air) X100%
=1.5/7.5 X 100%
= 20%
About 20% by volume of air is used up during combustion and the 80% of air left does not react with heated Copper.
In this experiment, the glass wool plug is used to stop the Copper turnings from being sucked int the syringes.
The air is passed repeatedly over heated Copper to ensure that all Oxygen in the syringes and tube is used up
The air is passed slowly to allow enough time of contact between the reactants.
The gas left in the syringe does not react