Osmolality, also called ionic molality, represents the number of dissolved particles in a solution. And we're going to say that when it comes to covalent compounds, the number of ions that they have is just one. Here they don't break up into multiple particles or ions, we just keep them together as one molecule, so for them it equals one.
Now the OSMO Wilding formula is that osmolality equals the number of ions times the molality of our solution and our compound. The way we approach this is we break up ionic compounds into ions and we count the total number of ions and multiply by molality of solution.
So if we take a look here, we have 2.5 molal of sodium chloride. Sodium chloride is an ionic compound that breaks up into two ions, sodium ion and chloride ions. That's a total number of two ions. So we're going to say here that the osmolality equals 2 because there's two ions times the molality of our solution.
So again, what's 2.5 molal of sodium chloride solution? That would mean that our total ionic molality here would be 5 mole. So that's the approach you need to take when it comes to ionic modality, otherwise known as osmolality.
