During the investigation, the volume of the air will decrease steadily as the oxygen in it is used up.
Copper + oxygen → copper oxide
Eventually, all the oxygen in the air will be used up to form copper oxide. The apparatus is allowed to cool (as gases expand when they are heated) and it is observed that approximately 20 cm3 of the air has been used up. The conclusion of the investigation is that 20 per cent of the air is made up of oxygen.
The Fire Triangle Fuel
zz z
You need three conditions to make a fire happen: zz
Heat z z Oxygen
If you remove any part of the fire triangle, the fire will go out. Fire safety
Fires can be put out in a number of ways. Which part of the fire triangle is being taken away in the following situations?
1. Using a carbon dioxide fire extinguisher. 2. Using a fire blanket. 3. A fire engine spraying a fire with water. 4. Creating a fire line during a forest fire.
z
Fig. 14.1.4 Fire triangle
14.1
Fig. 14.1.5 A fire line in a forest
‘Silent killer’
In groups, discuss why carbon monoxide is referred to as the ‘silent killer’.
Incomplete Combustion of a Fuel
If there is not enough air (oxygen) for complete combustion of a fuel, the reaction is not completely finished. The word equation for the incomplete combustion of fuel is as follows:
Fuel (hydrocarbon) + oxygen → water + carbon monoxide
Carbon monoxide (CO) forms instead of carbon dioxide. Carbon monoxide is a colourless, odourless, toxic gas that, even in low concentrations, may lead to death.
To prevent poisoning by carbon monoxide: zz zz z z
Boilers should be serviced regularly. Rooms should be well ventilated.
Carbon monoxide detectors should be installed. 239 z Fig. 14.1.6
