Easy gen chem question....

[addis4ever]

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Alright maybe I'm not in the right state of mind today but can't seem to understand the answer.

A 2.0g sample of unknown metal M, was completely burned in excess O2 to yield 0.02224mol of the metal oxide, M2O3. What is the metal?

Answer: Sc

 

[bharat008]

Alright maybe I'm not in the right state of mind today but can't seem to understand the answer.

A 2.0g sample of unknown metal M, was completely burned in excess O2 to yield 0.02224mol of the metal oxide, M2O3. What is the metal?

Answer: Sc

M + O2 -> M2O3

this is the reaction but now you have to balance it

4M + 3O2 -> 2M2O3


so using stoichiometry

0.02224 mol of 2M2O3 -> 0.04448 mol of 4M

since for every mole of M2O3 that is produced, twice the amount of mole of M is consumed

since 2.0 grams was used

2g/0.04448 mol = 44.96 g

 

[addis4ever]

ok...i kinda understand but i thought 2g/.04448mol is actually the molar mass for M2O3 not just the metal.

 

[bharat008]

ok...i kinda understand but i thought 2g/.04448mol is actually the molar mass for M2O3 not just the metal.

Can't do that.. 2g of unknown Metal sample was used. It doesn't account for oxygen..

 

[addis4ever]

ok...i see where u're taking that 2g and .04448mol of metal to get the molar mass for the metal. But why can't you count Oxygen in the calculation?