Question

Question #3336d

Answer 1

`"CaO"` contains 71.47 % `"Ca"` by mass.

Explanation:

The percent by mass is an intensive property — it does not depend on the amount of substance you have.

The formula for mass percent is

`color(blue)(barul|stackrel(" ")("Mass %" = "mass of component"/"total mass" × 100 %)|)`

Let's assume that we have 1 particle of `"CaO"`.

Then we have 1 atom of `"Ca"` and 1 atom of `"O"`.

We can use the Periodic Table to compute the masses:

`bbul("Atoms"color(white)(m)"Mass/u")`
`color(white)(ll)"1 Ca"color(white)(mmm)40.08`
`ul(color(white)(ll)"1 O"color(white)(lmmm)16.00`
`color(white)(mll)"Total = 56.08"`

∴ `"Mass % Ca" = (40.08 color(red)(cancel(color(black)("g"))))/(56.08 color(red)(cancel(color(black)("g")))) × 100 % = 71.47 %"`