Calculating the amount of oxygen in a glass using candle burning time

Question

I would like to calculate the amount of oxygen or concentration of oxygen in a glass or conical flask using candle burning time.
I am thinking of a simple way to calculate this based on the fact that the atmosphere contains $21,%$ oxygen. But I am not sure if this would give correct values.
Here is what I am thinking about:
I could do a candle and glass experiment and count the time for burning of candle.
First I will take a glass with atmosphere air and then keep it inverted on burning candle and count the time for burning.
Next I will take a glass with oxygen-enriched air (with unknown concentration) and then keep it inverted on burning candle and count the time for burning.
Here is a simple formula using cross multiplication, I could use
$$x = frac{t_mathrm{OEA}}{t_mathrm{air}}cdot 21,%,$$
where $x$ is the concentration of oxygen-enriched air, $t_mathrm{OEA}$ is the time taken to burn in oxygen-enriched air, $t_mathrm{air}$ is the time taken to burn in atmospheric air.
Is this possible or is there a way to do this without having to buy oxygen sensors?

John Meacham · Answer

I think you will be better off measuring the volume change after complete burning.
A common demonstration  was to place a candle in a dish of shallow water and light it, then put a clear cup over it and see how much water was sucked into the bottom as the oxygen is consumed. utilizing the same effect in a more controlled way perhaps would be a straightforward way to get a rough oxygen concentration.
When calculating it remember that 2 oxygen molecules are replaced by a single co2 molecule and you will want your water deep enough so that when the heated air expands it doesn't escape out the bottom and account for temperature differences either by doing the math or waiting for the temp to be the same.
Fully burning steel wool and measuring the gain in weight due to the oxygen getting incorporated into solid iron oxides might also work.

DrMoishe Pippik · Answer

You might get better results using titration. Pick a substance that reacts fairly completely with atmospheric oxygen, and measure how much needs to be added to remove all the $ce{O2}$ from a known volume.
For example, you might use washed, fine, steel wool (washing is needed o remove processing oils) to remove oxygen, and methylene blue with alkaline glucose to detect any remaining $ce{O2}$.
You might also try the Winkler test to measure dissolved oxygen in water.

Calculating the amount of oxygen in a glass using candle burning time

2 Answers

Add your own answers!

Ask a Question