how many grams of oxygen gas will be produced if 125g of KClO3 is decomposed completely?

Answer 1

Hello, Rylee,

There are two ways to answer this question. I do the simplest first.

1. Calculate the percent O in KClO3. Take the total atomic mass of the 3 oxygens (16 amu each) and divide by the atomic mass of the entire molecule (122.5 amu) to arrive at 39.2% O in the original molecule (3 sig figs). Simply multiply that times the mass of KClO3 decomposed to find the grams of O released, which I find to be 48.96g, rounded to 49.0g with 3 sig figs. Note that the question asks for oxygen gas, so the correct form would be O₂, but the mass remains the same.
2. Calculate the mass of O₂ by using moles. This requires the molar mass of KClO₃ which is 122.55 g/mol. It also requires a balanced equation: 2KClO₃ = 2KCl + 3O₂
3. We start with 125g of KClO₃, so that means we have 125g/(122.55g/mole) = 1.53 moles of KClO₃ .
4. The balanced equation says we will get 3 moles of O₂ for every 2 moles of KClO₃ .To find the moles of O₂ produced from 1.53 moles of KClO₃ , multiply 1.53 moles KClO₃ by (3 moles O₂ /2 moles KClO₃). 1.53*1.5 = 1.53 moles O₂.
5. Covert moles O₂ to grams by multiplying by it's molar mass (32 g/mole) to yield 1.53 moles O₂ * (32 g O₂/mole O₂). This results in 48.9 grams O₂ , which is the same answer we got from the first approach, as would be expected.

I hope this helps,

Bob