Question

Calculate the mass of oxygen needed to react with 12g of magnesium

Answer 1

Answer:

There are two ways to work this out, one is a lot simpler than the other, I will post the simpler method here.

The relative formula mass of magnesium oxide, MgO (40), is just a sum of the mass of magnesium (24) and the mass of oxygen (16).

24 + 16 = 40

We are told that 24 g of Mg produces 40 g of MgO when it reacts with 16 g of oxygen. We only need 10 g of MgO, 1 quarter of that given in the question.

In order to produce 10 g of MgO, we therefore only need a quarter of what we needed to make 40 g of MgO.

So, we would only need 24 g / 4 = 6 g of Mg to produce 10 g of MgO.

Answer 2

Answer:

The correct answer is 7.90g of $O_2$.

The total mass of oxygen needed to react with 12g of magnesium is 7.90g.

Explanation:

So according to the question, lets start with a balanced chemical equation, and then use the unit-factor method to find the answer with one chain calculation.

Given in the question :

12g of magnesium.

Solution :

2Mg(s) + $O_2$(g) → 2MgO(s)

Therefore, 12.0g of magnesium needs Xg of oxygen.

Now, 12.0g x (1 mol Mg / 24.305 g Mg) x (1 mol $O_2$ / 2 mol Mg) x (32.0g $O_2$ / 1 mol $O_2$) = 7.90g $O_2$

OR

2Mg(s) + $O_2$(g) → 2MgO

Therefore, ratio is 2 : 1 Mg : $O_2$

Therefore,

$\frac{1}{2}$ x $\frac{12g Mg}{24.305g/mol}$ = 0.25 mole of Mg

And 0.25moles x 32g/mole = 7.9g of $O_2$

Hence, the correct answer is 7.90g.

#SPJ3