14. Solutions
Molality
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Osmolality, also called ionic molality, represents the number of dissolved particles in a solution. And we're gonna say that when it comes to covalent compounds, the number of ions that they have is just 1. Here they don't break up into multiple, particles or ions. We just keep them together as 1 molecule, so for them it equals 1. Now the osmolality formula is that osmolality equals the number of ions times the molality of our solution and or 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 molarity of solution. So if we take a look here, we have 2.5 mol of sodium chloride. Sodium chloride is an ionic compound that breaks up into 2 ions, sodium ion and chloride ions. That's a total number of 2 ions, so we're gonna say here that the os molality equals 2, because there's 2 ions, times the molality of our solution. So again, it's 2.5 mol 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 molality, otherwise known as ossemolality.
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