Solutions are difficult for some students. Among those difficulties, we can find the use of mass percent as concentration: their meaning and how to relate to concentration in g/L. On the other hand, there are problems to dinstinguish between concentration (g/L) and density.
In order to confront those difficulties, sector diagrams can be used:
Here, the smallest circle represents a solution of 100 grams and the largest one liter of solution. Masses are different in both samples but ratio remains the same.
Students should determine relevant values and sector diagrams can help visualize involved magnitudes.