Molarity is a concentration unit that expresses concentration as moles of solute per liter of solution. A solution consists of two components, the solute and the solvent. The solute is what's dissolved, in this case sodium nitrate (NaNO3).
The amount of sodium nitrate was given in grams in this problem so we need to change it to moles by dividng by its molar mass:
185.0 g NaNO3 x (1 mole/84.99 g) = 2.177 moles NaNO3
Now we must convert the volume of the solution to liters:
750. ml x (1 liter/1000 ml) = 0.750 liters
We can now calculate the molarity:
(2.177 moles)/(0.750 liters) = 2.90 moles/liter = 2.90 M
Molarity is commonly used in chemistry calculations because of its relationship to moles. Since molarity = moles/liter, moles = molarity x liters. This makes it easy to find numbers of moles of substances that react in aqueous solutions.
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