# Question #27fd7

##### 1 Answer

#### Explanation:

The idea here is that you need to use the **molar mass** of *ferrous oxide*, **percent composition** of iron in this compound.

Once you know how many grams of iron you get **per**

So, ferrous oxide has a molar mass of **one mole** of ferrous oxide has a mass of

You also know that **one mole** of ferrous oxide contains

,one moleof iron#1 xx "Fe"# ,one moleof oxygen#1 xx "O"#

Elemental iron has a molar mass of **one mole** of iron has a mass of

This means that **every**

#"% Fe" = (55.845 color(red)(cancel(color(black)("g"))))/(71.844color(red)(cancel(color(black)("g")))) xx 100 = "77.73% Fe"#

So, if **every**

#5 color(red)(cancel(color(black)("g FeO"))) * "77.73 g Fe"/(100color(red)(cancel(color(black)("g FeO")))) = "3.8865 g Fe"#

Rounded to one **sig fig**, the number of sig figs you have for the mass of ferrous oxide, the answer will be

#"mass of Fe" = color(green)(|bar(ul(color(white)(a/a)"4 g"color(white)(a/a)|)))#