Concentration concepts
By the end of this lesson
- Distinguish amount from concentration
- Convert compatible mass-per-volume units
- Separate stock and final-medium values
Examples use a decimal point; a comma groups thousands.
See it
Concentration expresses an amount of a substance relative to a defined volume or amount of solution. Common forms include mass per volume, molarity, and stock-to-working relationships. The Academy focuses on interpreting the unit correctly before calculation.
Understand it
Distinguish amount from concentration
mg/L and g/L differ by a factor of 1,000.
Concentration relates an amount of substance to a defined amount or volume of solution.
Convert compatible mass-per-volume units
Molar concentration depends on molecular amount, not simply mass.
Converting grams to milligrams multiplies the mass value by 1,000 while keeping the per-liter basis.
Separate stock and final-medium values
The same chemical can appear as a stock concentration and a much smaller final concentration.
A per-liter concentration specifies a ratio; the actual mass in a container depends on its volume.
Worked example
A solution labeled 0.5 g/L contains 500 mg per liter. This concentration is not the same as adding 500 mg to every vessel regardless of its fill. A stock and a final medium can contain the same chemical at different concentrations.
Explain your decision before opening the worked reasoning below.
Show the worked reasoning
Stock and final-medium concentrations may differ substantially even when they describe the same chemical.
Molar concentration expresses amount of substance rather than simply mass, so changing concentration types requires explicit conversion.
Do not mix concentration units in one calculation without explicit conversion.
Try it
Why is 500 mg/L not 500 mg per vessel?
Use the worked example above to explain your answer in your own words before taking the quiz.
Lesson quiz
Assessment version: 2026-10-15-v2. Previous reading-completion markers are retained. This revised quiz has its own result.
Apply it
Use the worked example to write a short decision record: what did you observe, which rule did you apply, and what would you check before acting?
Completion marks reading progress, not a quiz pass or professional certification.