Concentration MattersSometimes, how much stuff you have is less important than how concentrated it is.
Consider two bottles of Kool Aid, each with 1 scoop of powder added:
vs
Concentration MattersSometimes, how much stuff you have is less important than how concentrated it is.
Consider two bottles of Kool Aid, each with 1 scoop of powder added:
vsI’m going to drink the good one
Concentration UnitsAll units of concentration are a ratio (what else?):
amount of stuff dissolved vs how much it’s dissolved in(solute) (solvent)
The mixture of the two is a solution
There are many units out there, but most of them are bad:
Concentration UnitsAll units of concentration are a ratio (what else?):
amount of stuff dissolved vs how much it’s dissolved in(solute) (solvent)
There are many units out there, but most of them are bad:
Percent: The vinegar was listed as 5% acid. The problem is, 5% by what? The unit is unclear
5% by weight ≠ 5% by volume ≠ 5% by moles
Concentration UnitsAll units of concentration are a ratio (what else?):
amount of stuff dissolved vs how much it’s dissolved in(solute) (solvent)
There are many units out there, but most of them are bad:
Percent: The vinegar was listed as 5% acid. The problem is, 5% by what? The unit is unclear
5% by weight ≠ 5% by volume ≠ 5% by moles
Mass per volume: usually given in grams per 100 mL. This is better, because at least you know the units, but there’s still a problem:
5 g/100 mL NaCl (aq) is more concentrated than 5 g/100 mL CaCl2 (aq)
Calcium chloride is heavy, so five grams is actually less stuff (fewer formula units)
An Annoying DetailLet’s say I’m making that 3M salt solution. I go and get myself 6 moles of salt, and 2 liters of water:
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