# What is percent composition in chemistry?

"% composition"="quantity of stuff"/"quantity of stuff + quantity of solvent"xx100%
Most of the time we quote a percentage by mass....which is defined by the given quotient....i.e. "weight"/"weight"xx100%. The term $\text{part per million}$ is for trace quantities in aqueous solution...and refers to the quotient...$\text{milligrams of solute"/"litres of solution}$...where $1 \cdot L$ $=$ $1000 \times 1000 \cdot m g = {10}^{6} \cdot m g$, i.e. one million milligrams....