Percentage of Oxygen in the Air Flashcards
What experiments are used to determine the percentage of oxygen in the air?
The bell jar
Copper
Iron and oxygen
How do you find the percentage of oxygen?
Volume of oxygen
————————— x 100%
Volume of air
Why does the volume of the air inside the bell jar increase initially?
The air is expanding as it gets heated
With what colour flame does the phosphorus burn?
Yellow
What does the white phosphorus look like?
White / yellow
Why does the volume of air inside the bell jar increase initially?
The air is expanding as it gets heated
Why must we wait for the ‘air’ to cool down before we measure the new volume?
To allow the air to cool and contract
Why must we make sure the water level outside the jar is the same as that is did the jar before measuring the volume?
Atmospheric pressure - to keep it the same
Why does the large pile of copper turn black?
Is it reacting with the oxygen - being oxidised - as the air moves over it each time, forming copper oxide
Why is the gas allowed to cool before its volume is measured?
It is still expanding (heat)
The small pile of copper powder is then heated and the remaining gas is passed several times over the hot copper. The copper does not turn black. Why?
All of the oxygen has been used up - there is not enough left.
What is the advantage of using iron powder, rather than pieces of iron?
Reaction rate increases
Why is it nessecary for the student to mix the iron power with water?
So that the iron powder is damp
