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PEAZIT Aha card

Concentration: the part belongs to the whole solution

Mass fraction w is solute mass divided by total solution mass. The solution includes both solute and solvent. Multiply by 100 to obtain mass percent.

Concentration: the part belongs to the whole solution

Observation	What it means
10 g salt + 90 g water	100 g solution
10/100 = 0.10	10% by mass

One worked example

5 g salt + 45 g waterFirst add the masses.
solution mass = 50 gThe denominator is the whole solution.
w = 5/50 = 0.1 = 10%Convert the fraction to a percentage.

Watch out: Mass percent differs from volume percent and molar concentration.

Goal, prerequisites and card origin

What you will learn: Calculate mass percent.

What you need first: Percentages and mass.

An original PEAZIT working card. Independent expert review and effectiveness testing have not yet taken place. · v1

Reference for the underlying principle ↗

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Mass fraction w is solute mass divided by total solution mass. The solution includes both solute and solvent. Multiply by 100 to obtain mass percent.

Without JavaScript, write your answer elsewhere before opening the solution.20 g salt is dissolved in 80 g water. What is the mass percentage of salt? Enter a number without %.

Solution — open after your own attempt

20 Solution mass is 100 g; 20/100 × 100 = 20%.

A question for your next return: How many grams of solute are in 200 g of a 10% by-mass solution? Enter a number.

Solution — open after your own attempt

20 0.10 × 200 = 20 g.

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