Molarity

Molarity

Molarity is a common way to express the concentration of a solution.

The symbol for molarity is M. Molarity is equal to the number of moles of solute in one liter of solution.

M =	moles of solute
	1L of solution

If you are told to use 6.0 M HCl solution in an experiment, that means that there are 6.0 moles of HCl in 1 liter of that HCl solution.

Using Molarity as a Conversion Factor

How many moles of HCl are in 20 mL of 6.0 M HCl?

We know that 6.0 M HCl can be written as

6.0 moles HCl/1 L solution or

1 L solution/6.0 moles HCl.

So that the units will cancel, we must convert 20 mL to L first. Then we will use the first conversion factor so that the units of L will cancel and leave the answer in moles.

		Conversion factor		Molarity
20 mL solution	x	1 L	x	6.0 moles HCl	=	0.12 moles HCl
		1000 mL		1 L solution

So there are 0.12 moles of HCl in 20 mL of 6.0 M HCl solution.

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