Worked example
A solution contains 15 g of solute in a final volume of 0.50 L. Its mass concentration is 30 g/L. Adding water until the final volume is 0.75 L changes it to 20 g/L. The 15 g stays the same; the volume in the denominator changes.
Contrast and common error
A bigger container can contain more grams without being more concentrated. Convert volumes to the same unit before comparing. When a prompt states how much water was added but does not say volumes add, use the supplied final solution volume when available.
Transfer check
Two solutions contain 4 g in 200 mL and 9 g in 300 mL, respectively. Which is more concentrated? Check: 4 ÷ 0.20 = 20 g/L and 9 ÷ 0.30 = 30 g/L, so the second is more concentrated.
Try it, then explain it.
Complete a short set without looking at the example. After each answer, explain which evidence or rule supports your decision and why the alternatives do not fit.
Sources & authorship
Original OpenExam explanations and examples. References support the concepts; they are not the source of copied questions. Independent educator review is pending.
OpenStax Chemistry 2e 3.3 Molarity