Question

The chemical equation below shows the burning of magnesium with oxygen to form magnesium oxide 2Mg + 02 --> 2MgO the molar mass of O2 is 32.0g/mol. what mass, in grams, of O2, is required to react completely with 4.00 mol of Mg? a. 2.00 b. 64.0 c. 128 d. 256

Answer 1

Answer:

The required mass of oxygen to react with 4 moles of Mg is 64 grams

Explanation:

You know the reaction where magnesium is burned with oxygen to form magnesium oxide:

2Mg + $O_{2}$ --> 2MgO

Oxygen is required to react completely (that is, sufficient oxygen must be present for the reaction to occur) with 4 moles of Mg. For that you observe the stoichiometry of the reaction, the amount of reagents needed. Stoichiometry in this case tells you that in order for 2 moles of Mg to react, you need 1 mole of $O_{2}$. Taking this into account, you apply a rule of three: if to react with two moles of Mg you need 1 mole of $O_{2}$, how many moles of $O_{2}$ do you need to react with 4 moles of Mg?

$moles of O_{2} =\frac{4 molesMg*1molO_{2} }{2 molesMg}$

moles of O_{2} =2 moles

To know the mass of $O_{2}$ that reacts, you must take into account the molar mass of oxygen, which is 32 grams / mol and you can apply another rule of three: if in a mole of $O_{2}$ there are 32 grams, how many grams are in 2 moles of oxygen?

$mass of oxygen=\frac{2 moles* 32 grams}{1mol}$

mass of oxygen= 64 grams

Then, the required mass of oxygen to react with 4 moles of Mg is 64 grams

Answer 2

B.) 2Mg + 02 --> 2MgO. According to stoichiometry, 2 moles of Mg reacts with 1 mole of O2. Therefore 4 moles of Mg will react with 2 moles of O2. Therefore mass of O2 required = moles of O2 x molar mass of O2 = 2 x 32 = 64 grams.