Firstly, what do vinegar and baking soda have to do with carbon
dioxide? Well if you've looked at the pH
experiment on this site you may have realized that vinegar is
an acid and baking soda a base. To be specific, vinegar contains
acetic acid and baking soda, sodium bicarbonate, and they react
together in an acid-base reaction (top reaction) to give a gas
and a salt. One of the products of the reaction decomposes to
give water and carbon dioxide (bottom reaction).
So that is how we got the carbon dioxide, but why does it put
out the flame? Carbon dioxide is heavier than air so when you
pour it out of the glass it sinks. Because air contains around
0.04% carbon dioxide, the gas from the glass will gradually diffuse
so that all the air in the room has an equal concentration but
this isn't quick enough to stop it from putting out the flame
1st.
A fire is a type of chemical reaction - it is the oxidation of
some sort of fuel such as wood, organic matter or petrol. Spontaneous
combustion luckily is fairly rare as you require a heat source
or spark for a fire to start. For wood, it has to heated to a
temperature of 325 degrees Celsius before it bursts into flames,
a match is a much easier way to start a fire. A fire needs around
16% oxygen in the air to burn, our atmosphere is around 21%. Forest
fires tend to spread so fast because wind constantly brings in
a fresh supply of oxygen. Because a fire needs oxygen to burn,
covering it in a blanket of carbon dioxide acts to smoother it
and it therefore goes out.
