Question

Niven wants to calculate the mass of MgO that is produced by the burning of 28.0 g of Mg. What is the first step in Niven’s calculation?

Answer 1

The first step would be to write a balanced reaction between Mg and O2 forming MgO

Step-by-step explanation:

Step 1: Write the balanced chemical reaction between Mg and O2

`2Mg + O2\rightarrow 2MgO`

Based on the reaction stoichiometry:

2 moles of Mg produces 2 moles of MgO.

Therefore the ratio, Mg:MgO = 1:1

Step 2: Calculate the moles of Mg reacted

Atomic mass of Mg = 24 g/mol

Mass of Mg reacted = 28.0 g

Moles of Mg =
`(Mass)/(Atomic\ Mass) = (28.0)/(24) = 1.167`

Step 3: Calculate the mass of MgO produced

Moles of Mg reacted = moles of MgO produced = 1.167

Molar mass of MgO = 24 + 16 = 40 g/mol

Mass of MgO =
`moles* molar\ mass = 1.167*40 = 46.7 g`

Answer 2

I would say that Niven would have to calculate the atomic weights of Mg and O and then the total weight of MgO to get the percent of oxygen and then that way get a proportionate amount of the 28 grams of oxygen required to bond with the Mg and then add together the weight of Mg which would be 28.0 grams plus the weight of oxygen.