# Question 3336d

Sep 4, 2017

$\text{CaO}$ contains 71.47 % $\text{Ca}$ 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 $\text{CaO}$.

Then we have 1 atom of $\text{Ca}$ and 1 atom of $\text{O}$.

We can use the Periodic Table to compute the masses:

$\boldsymbol{\underline{\text{Atoms"color(white)(m)"Mass/u}}}$
$\textcolor{w h i t e}{l l} \text{1 Ca} \textcolor{w h i t e}{m m m} 40.08$
ul(color(white)(ll)"1 O"color(white)(lmmm)16.00#
$\textcolor{w h i t e}{m l l} \text{Total = 56.08}$

$\text{Mass % Ca" = (40.08 color(red)(cancel(color(black)("g"))))/(56.08 color(red)(cancel(color(black)("g")))) × 100 % = 71.47 %}$