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In chemistry, concentration is oftentimes given in molarity. (abbreviated
M)
Molarity refers to the number of moles of solute per liter of solution. For example, if I have 1 liter of a solution that contains 2.5 moles of a substance dissolved in it, it would be a 2.5 molar solution or 2.5
M.
Molarity = moles of solute ÷ liters of solution
Remember that the solute is the substance that gets dissolved and solution is both the solute and solvent together.
To calculate this you need to make sure that you are dealing with the correct units.
For example, say you are given the following information...
35 g of NaCl are dissolved in enough water to create 750 mL liters of solution. What is the concentration?
You first have to convert the grams NaCl to moles NaCl and the mL to L.
This would be 0.5989 mol NaCl and 0.750 L
By dividing moles by liters we get a concentration of 0.7985
M.