Oxygen from potassium chlorate

You will write three functions for the reaction $2\text{KClO}_{3}\ \rightarrow \ 2\text{KCl}\ +\ 3\text{O}_{2}$. The first finds the volume of oxygen from a mass of the salt. The second finds the mass of the salt that is needed for a volume. The third finds the percentage of a mixture that is the salt.

The idea. Three moles of oxygen come from two moles of the salt. One mole of gas fills 22.4 L at 273 K and 1 atm.

Your tasks.

1. Complete oxygen_volume(mass) so that it returns the litres of oxygen for a mass of KClO3 in grams.
2. Complete chlorate_needed(volume) so that it returns the grams of KClO3 for a volume of oxygen in litres.
3. Complete percent_in_mixture(volume, mixture_mass) so that it returns the percentage of KClO3 in the mixture.