Thanx alot guys!?

Question

When magnesium is bured in the presence of oxygen the magnesium and oxygen combine to produce magnesium oxide There are 6 grams of magesim and 4 grams of oxygen If 8 grams of magnesium oxide is produced and all the mageium was used up haow many grams of oxygen are left?

Answer 1

The equation is :
2 Mg + O2 >> 2 MgO
6 g / 24.3 = 0.247 mole of Mg
4 g / 32 = 0.125 mole of O2
the ratio between Mg and O2 is 2 : 1
8 g/ 40.3 = 0.199 mole MgO produced
the ratio between O2 and MgO is 1 : 2
1 : 2 = x : 0.199
x = 0.0995 mole of O2 needed for the reaction
Mole of O2 that are left = 0.125 - 0.0995 = 0.0255 mole
0.0255 mol x 32 g/mol =0.816 g of O2
Of course it is impossible to use all the magnesium

Answer 2

2Mg + O2 --> 2MgO
8 g of MgO = 8/40.32 moles or 0.1984 moles of MgO
However 6 g of Mg = 6/24.32 = 0.247 moles of Mg
The problem says all the Mg was used. If so, the weight of the MgO is wrong because 1 mole of Mg will produce 1 mole of MgO and 0.1984 <> 0.247

Answer 3

6gMg x 1molMg/24gMg x 1molMgO/1molMg x 40gMgO/1molMgO = 10g MgO

4gO2 x 1molO2/32gO2 x 2molMgO/1molO2 x 40gMgO/1molMgO = 10g MgO

So if you use all the Mg, there is 10g MgO produced, not 8g. And the amount of O2 left over is 0.