[JessePinkman]

I must know the answer to the following question, no strings attached:

What is the theoretical yield of magnesium oxide with 0,49 grams of magnesium?

[Arkcon]

Ok, you will need a balanced chemical equation first.   The question begins with what you get, MgO and ends with what you start with, Mg.  So, what else do you need?  And can you put it together in a chemical reaction, that you've balanced.

[JessePinkman]

2Mg + O₂ 2MgO

Right?

I guess you could say the amount of O is not a problem, I only need to worry about my 0,5g's of Mg.

[thetada]

Equation is correct, and your assumption about oxygen seems reasonable in the absence of any other data.

[JessePinkman]

Nice... Now, gib answer, please?

[thetada]

Do you know how to work out the number of moles of magnesium you have?

[JessePinkman]

We haven't and won't read about this until high school, I honestly just want to impress my teacher and make it look like I know something about chemistry, so my answer is "no". While we're at it, what's potasium benzoate? Also, magnets. How do they work?

[thetada]

I can't tell you the answer but I'll happily show you the technique.

If we had 5g of calcium and excess oxygen, we can work out the theoretical yield of calcium.

the number of moles of Ca is 5/40 = 0.125

the relative mass of Calcium is 40, meaning that 1 mole of Ca has a mass of 40g. (The relative mass of each element is shown on the periodic table.)

moles are a way of counting the number of particles in a sample. Calcium atoms are heavier than magnesium atoms, so if you had 5g of each, you would have more atoms of magnesium.

the equation for the oxidation of calcium is similar to the Mg equation

2Ca + O₂  2CaO

What this means is that 1 mole of Calcium produces 1 mole of Cao, so if we have 0.125 moles of Ca, we'll get the same number of moles of CaO

The relative mass of CaO is calculated by adding the relative masses of calcium and oxygen, which is 40 + 16 = 56

so, the mass of CaO produced is 56 x 0.125 = 7g

You can use the same technique to figure out the mass of MgO produced.