" If 45g KCl are dissolved in 100 grams of water at 20 degrees Celcius what type of solution does it form? "
A solubility curve shows us how solubility of solute in a solvent changes as temperature changes.
Points on the curve give us the concentration in grams (per 100grams) of a saturated solution at that temperature.
Points below the curve give concentrations for unsaturated solution Points above the solubility curve give concentrations for supersaturated solution
Mass is chosen primarily because the mass does not change with temperature, as the density of water changes with temperature ( when water is heated its density decreases ).
We can use the solubility curves to : Determine how much solute will dissolve in the solvent at a given temperature, determine the mass of solid precipitated out of solution when the temperature of the solution changes, compare the solubilities of different solutes in the same solvent.