[Auroturtle]

So I got my Chemistry test back, and I need to retake it. One question I got wrong was:

"When (C₂H₂) burns, how many liters of O₂ at STP are used for every 4.0 mol of (C₂H₂) burned?"

Of course I write the balanced equation:

"2(C₂H₂) + O₂  2(C₂) + 2(H₂O)" , which means 4 mol of acetylene is 2 mol of oxygen

I use (PV/nT)=r

V
______ = 0.08206
2 x 273

the answer is get is 44.8L... but the correct answer is 224L

1) What did I do wrong?
2) How do you know when to divide by 2, like when its a diatomic gas (O₂)?

[sjb]

So I got my Chemistry test back, and I need to retake it. One question I got wrong was:

"When (C₂H₂) burns, how many liters of O₂ at STP are used for every 4.0 mol of (C₂H₂) burned?"

Of course I write the balanced equation:

"2(C₂H₂) + O₂  2(C₂) + 2(H₂O)" , which means 4 mol of acetylene is 2 mol of oxygen

Whilst the equation you have written is balanced, it does not represent complete combustion. What happens when carbon burns?

[Auroturtle]

Yeah sorry the balanced was wrong, I forgot CHO.... I guess the question is resolve, lol.

[rabolisk]

Just to be clear.. What is the correct balanced reaction?

[Auroturtle]

2C₂H₂ + 5O₂   4CO₂ + 2 H₂O


And can you please look at my other question, is it possible the teacher had the wrong answer for the test?

[DrCMS]

So using the correct balanced equation how much oxygen is required in moles and then in L?  This time your teacher is correct.