Magnesium reacts with oxygen to form magnesium oxide. How many L of oxygen gas at STP are needed to react?

Question

completely with 8.0g of magnesium? 2Mg + O2 --- 2MgO
thanks for your help!!!!

this is what i did:
8.0g Mg/24.31g * 22.4L/22.4L = 33mol O2 so 33mol O2 x 22.4L O2 = 7.4L O2 is this correct????

Answer 1

This is bookkeeping. Convert g Mg to moles Mg, and use the equation to see how many moles O2 that corresponds to. (You always have to do something like this when balancing amounts of two different substances.)

Then you can either use PV= nRT (you just found out n), or

V = 22.4L x n at STP

Whichever you prefer. They must give the same answer.

Answer 2

Atomic wt of magnesium = 24.3

Atomic wt of oxygen= 16

2 x 24.3 = 48.6 gms of Mg requires 16 x 2 = 32 gms of oxygen

8 gms of Mg will need = 8/48.6 x 32 gms of oxygen
= 5.267 gms oxygen

32 gms of oxygen = 1 mole of oxygen occupies 22.4 liters space

therefore, 5.267 gms occupies 3.69 liters

3.69 liters of oxygen will be required