Determining the concentration (Molarity) of a solution

20 points

Name:__________________________________        Period:______________

There are 3 ways to state the concentration of a solution.

Molarity - The number of moles of a solute dissolved in enough solvent to make 1L of solution.  The abbreviation is "M", as in a 1M solution. A 1 molar solution.

Molality - The number of moles of a solute, dissolved in 1L of solution.  The abbreviation is "m" as in a 1m solution.

Parts per million - The mass of the component in solution divided by the total mass of the solution multiplied by 10⁶ (one million).  The abbreviation is "ppm"

By far the most important is MOLARITY (M).  We will concentrate on MOLARITY.

The molarity of a solution is the number of moles of a substance dissolved in enough solvent to make 1L of solution. 

The solvent does NOT have to be water!!!!

You determine the molarity of solution as follows:

1.    Determine the average atomic mass if the sample is an element, or the gram formula weight if it is a compound.

2.    Multiply the mass of the sample by 1/(grams/mole) (grams/mole is from step 1). 

1.    What is the molarity of 1L of solution produced by dissolving 8 grams of NaCl in H₂O?

8 grams NaCl X 1 Mole NaCl/ 58 grams NaCl = .44 moles NaCl

2.    What is the molarity of 100 grams of NaCl dissolved in 1 L of H₂O?

100 grams NaCl X 1 Mole NaCl/ 58 grams NaCl = 1.72M NaCl

Compute the number of moles of the substance in each of the following samples, and hence the molarity of a 1L solution.  Round to 2 places to the right of the decimal.  Attach solutions and show all work, as above.