# Question dc381

Jan 14, 2014

42.88 % $\text{C}$ by mass and 57.12 % $\text{O}$ by mass

#### Explanation:

Percentage composition is the percentage by mass of each element in a compound.

"% by mass" = "mass of element"/"total mass of all elements" × 100%

To find the % composition of $\text{CO}$, you calculate the % by mass of each element in a given mass of $\text{CO}$. It is simplest to use 1 mol of $\text{CO}$.

1 mol $\text{CO}$ contains 1 mol of $\text{C}$ and 1 mol of $\text{O}$.

28.01 g $\text{CO}$ contain 12.01 g $\text{C}$ and 16.00 g $\text{O}$.

"% C by mass" = "mass of C"/"mass of CO" × 100 % = (12.01 color(red)(cancel(color(black)("g"))))/(28.01 color(red)(cancel(color(black)("g")))) × 100 % = 42.88 %

"% O by mass" = "mass of O"/"mass of CO" × 100 % = (16.00 color(red)(cancel(color(black)("g"))))/(28.01 color(red)(cancel(color(black)("g")))) × 100 % = 57.12 %#