SME
Grade 10 Science · Problem type
Percent by mass
Use this for “15 g of sugar is dissolved in 135 g of water. What is the percent sugar by mass?”
Diagram
10% of 150 g is 15 g.
This is an example. Type your own values to start a new problem.
p (%)
=
m₁ (g)
m (g)
×
100
m₂
Mass of solvent
example · g
Formulas
m
=
m₁
+
m₂
150 = 15 + 135
p
=
m₁
m
×
100
10
=
15
150
×
100
Assumptions
•
The solution’s mass is the solute’s and the solvent’s together.
•
Percent by mass is the solute’s share of the solution’s mass, not of the water’s.
Step-by-step
WE KNOW
m₁ = 15 g, m₂ = 135 g
FIND
mass of solution (m), percent by mass (p)
Step 1 · Find mass of solution (m)
Use m = m₁ + m₂
Dissolving loses no mass: add the solute and the solvent.
m
=
15
+
135
m
=
150
g
Step 2 · Find percent by mass (p)
Use p = m₁/m × 100
The solute’s share of the whole solution, as a percent.
p
=
15
150
×
100
p
=
10%
Check
Put the numbers back in. Both sides should match.
150 = 15 + 135 ✓
10
=
15
150
×
100
✓
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