Chem Notebook COmplete

Part 5: Molarity
Molarity (M) is the most common measure of concentration. The concentration of most solutions
you see in the lab are expressed in terms of molarity. Just like g/L, molarity calculations require
that you know either the volume or density of the resulting solution.
Notes:
Using Density to Calculate Molarity
If the volume of the resulting solution is not known, molarity is calculated as follows:
Convert the volume of solvent to grams. (The simulation does this step for you.)
Determine the total mass of the solution (mass of solute + mass of solvent).
Convert the solution mass to volume in milliliters, using its density (volume = mass / density).
Convert the solution volume to liters (divide by 1000).
Convert solute grams to moles.
Calculate the molarity (moles solute / L solution).
Reinforcing What You've Learned
1. 35.0 g potassium dichromate are dissolved in 354.0 g distilled water. What is the concentration
of the resulting solution, expressed as percent by mass? 9.00%
2. A chemist discovers that 2587.0 g distilled water are contaminated with 13.0 g NaNO3. What is
the concentration of NaNO3, expressed in ppm? 5.00 X 10 3
3. 175.00 g H2SO4 are added to 61.49 g distilled H2O. What is the molality of the resulting solution?
29.04m
4. 225 g NaBr are dissolved in 525 g distilled water. If the volume of the resulting solution is
584 mL, what is its concentration when expressed in g/L? 385g/L
5. 470.0 g Na2CO3 are dissolved in 4230.0 g distilled water. What is the molarity of the resulting
solution (D = 1.1029 g/mL)?
1.1561 M
Applying What You've Learned
6. Think about the equations for mass percent and parts/million. Consider how you might convert
between these two measures of concentration.
Mass percent = ppm ÷ 10,000 ppm = mass percent X .0001
7. Think about the equations for grams/liter and molarity. Consider how you might convert
between these two measures of concentration.
grams / L = molarity X molar mass
molarity = grams / L ÷ molar mass