In a reacting flask, 500 cm3 hydrogen is mixed with 500 cm3 oxygen and is ignited. (a) Which reactant is the limiting reagent? (b) Calculate the mass of water formed.

See Explanation

Explanation:

From Gay-Lussac's law of combining volumes;

Equation of the reaction; 2H2(g)  + O2(g) > 2H2O(g)

Ratio of volumes;              2           :    1                :    2

Initial volumes;                  500cm^3   500cm^3       0 cm^3

Reacting volumes;          500cm^3    250cm^3      500cm^3

Final Volumes;                0 cm^3        250 cm^3     500 cm^3

We can easily see from the table that the limiting reactant is oxygen.

Hence, the mass of water formed is obtained from;

1 mole of gaseous water occupies 22400 cm^3

x moles of water occupies 500cm^3

x = 500cm^3 * 1 mole/22400 cm^3

x = 0.022 moles of water

Mass of water = 0.022 moles of water * 18 g/mol

Mass of water = 0.396 g

it is the most commonly accepted one