How do you determine the saturation point of a solution?

Question

If I'm dissolving a certain amount of Potassium Nitrate in water at a certain temperature, how can I find out the exact amount of solute (i.e. Potassium Nitrate). Something other than adding a lot of the compound and measuring the excess that is left behind.

Answer 1

The saturation point of a solution is temperature dependent, therefore, it is to be determined at a particular temperature.It can be known by theoretical calculations as well as by practical observations.
For theoretical calculations standard solubility curves for different temperature are available in the Books, and can be used directly.
Second option can be through Solubility product calculations. solubility products for various solutions are available in the literature ,from which solubility of the compound at different temperatures can be estimated.

By practical experiments ,if the saturation point is to be determined say at 30deg C,then the solute is added to a known quantity of water at say 35 deg C till no more can go into solution,then the solution is cooled to 30 deg C and wt. of the solute settled during cooling is determined. From which saturation point can be determined.

Answer 2

That's what the Ksp is for! Look up the Ksp for the given solid. There is a way to calculate the (max.) solubility of a given solid, from the Ksp, based on how many ions are in the salt. Crack open ANY general chem text, or google "solubility product constant" and you'll likely find very easy to follow instructions on how to do this.

If the salt has only one anion and one cation (like NaCl), then the solubility, S, is the square root of the Ksp, because
Ksp = (Na+)(Cl-) = (S)(S) or S^2. Solve for S, it's the square root of the Ksp.

If it's got three ions, like CaCl2, then you have to solve for S from this: Ksp =(Ca2+)(Cl-)^2, or (S)(2S)^2, or 4S^3

The only disadvantage to this method is that it's for use at STP. You will need to look up a solubility curve to see how it varies with temperature. Or, again, crack open your text.

The more complicated the salt, the more complicated the Ksp expression. Google this or look it up on Wikipedia, it's all there in plain English.

Answer 3

This factor of optimal concentration, the saturation factor, relies upon on the temperature of the liquid as well because the chemical nature of the aspects in contact. this may be utilized interior the technique of recrystallisation to purify a chemical - wikipedia

Answer 4

The solubility curves for many items such as KNO3 are well known. The chemistry book we use (Prentice Hall) has it right in the book. Perhaps you can look it up on-line