Molar solubility is commonly expressed in which unit?

Molar solubility is commonly expressed in which unit?

• A. moles per liter
• B. grams per liter
• C. moles per kilogram
• D. percent by mass

Answer: (A)

Expressing solubility as a concentration is the key idea. Molar solubility refers to how many moles of solute dissolve in enough solvent to form a saturated solution, and this is most usefully written as molarity—moles per liter of solution. Using moles per liter lets you plug directly into reaction and equilibrium calculations (like Ksp) and compare solubilities across different substances and temperatures on a common scale. Grams per liter ties the amount to molar mass, making it less universal for comparing solubilities. Percent by mass depends on the total solution mass and isn’t a straightforward concentration, and molality (moles per kilogram) is another valid unit but is not the standard for reporting solubility in solution. Therefore, the usual expression is moles per liter.

Expressing solubility as a concentration is the key idea. Molar solubility refers to how many moles of solute dissolve in enough solvent to form a saturated solution, and this is most usefully written as molarity—moles per liter of solution. Using moles per liter lets you plug directly into reaction and equilibrium calculations (like Ksp) and compare solubilities across different substances and temperatures on a common scale. Grams per liter ties the amount to molar mass, making it less universal for comparing solubilities. Percent by mass depends on the total solution mass and isn’t a straightforward concentration, and molality (moles per kilogram) is another valid unit but is not the standard for reporting solubility in solution. Therefore, the usual expression is moles per liter.