Question

Question #15857

Answer 1

`72.71%`

Explanation:

The idea here is that you need to figure out how much oxygen is present in `"100 g"` of carbon dioxide `->` this number will give you the percent composition of oxygen in carbon dioxide.

Since you know that every mole of carbon dioxide contains

• one mole of carbon, `1 xx "C"`
• two moles of oxygen, `2 xx "O"`

you can say that a mass of carbon dioxide that is equivalent to `1` mole of this compound will contain the mass of `2` mole of oxygen.

Now, carbon dioxide has a molar mass of `"44.0095 g mol"^(-1)`, which means that `1` mole of this compound has a mass of `"44.0095 g"`. Oxygen has a molar mass of `"15.9994 g mol"^(-1)`, and so `1` mole of oxygen has a mass of `"15.9994 g"`.

Therefore, you can say that `2` moles of oxygen will have a mass of

`2 color(red)(cancel(color(black)("moles O"_2))) * "15.9994 g"/(1color(red)(cancel(color(black)("mole O"_2)))) = "31.9988 g"`

Since this is how much oxygen you get in `"44.0095 g"` of carbon dioxide, you can say that `"100 g"` of carbon dioxide will get you

`100color(red)(cancel(color(black)("g CO"_2))) * "31.9988 g O"/(44.0095color(red)(cancel(color(black)("g CO"_2)))) = "72.71 g O"`

This means that the percent composition of oxygen in carbon dioxide is

`color(darkgreen)(ul(color(black)("% composition CO"_2 = "72.71% O")))`

I'll leave the answer rounded to four sig figs.