Percent by mass is the mass of the solute divided by the mass of the solution, multiplied by 100.

##”% by mass” = “mass of solute”/”mass of solution” × 100 %##

##=”mass of solute”/”mass of solute + mass of solvent”× 100 %##

Step 1 — Determine the mass of the solute.

The mass of solute is 2 g.

Step 2 — Determine the mass of solution.

##”mass of solution” = “mass of solute + mass of solvent “=”2 g + 18 g = 20 g”##.

Step 3 — Determine percent by mass of the solute.

##”% by mass” = “mass of solute”/”mass of solution” × 100 % = (2 color(red)(cancel(color(black)(“g”))))/(20 color(red)(cancel(color(black)(“g”)))) × 100 % = 10 %##

The mass percent of the solute is 10 %.