1. The problem statement, all variables and given/known data 50cm^3 of a mixture of CO, CO2 and H2 were exploded with 25.0cm^3 of O2. After explosion, the volume measured at r.t.p. was 37.0 cm^3. After treatment with aqueous KOH, the volume was reduced to 5.0cm^3. Calculate the % composition by volume of the original mixture. 2. Relevant equations 3. The attempt at a solution From this, I can safely assume that CO will react with O2 to form CO2 2CO + O2 --> 2CO2 and 2H2 + O2 --> 2H2O and CO2 will not react with Oxygen. When treated with KOH, the steam and carbon dioxide will all be removed. I assumed that 5.0cm^3 of oxygen is left. However, what I don't understand is how did the total volume of gas decrease from 75cm^3 (including oxygen) to 37.0cm^3?