Molarity & Dilutions Notes
Concentration
Measure of how much solute is dissolved in a specific amount of solvent/solution.
A concentrated solution contains larger amount of solute.
A dilute solution contains a smaller amount of solute.
Molarity (M)
Moles of solute / liters of solution
Also known as molar concentration
It’s unit is M (read/pronounced a molar)
Units Table
Examples:
What is the molar concentration of a liter solution with 0.5 mol of solute?
Molarity = moles of solute / liter of solution
= 0.5 mol solute / 1 L solution
= 0.5 M
If you have a 100.5 mL IV (intravenous) solution containing 5.10 g glucose
(C6H12O6). What is the molarity of the solution? (Molar Mass of glucose = 180.16
g/mol)
Molarity = moles of solute / liter of solution
Step 1:
Convert grams of solute glucose to moles solute using MM of glucose
5.10 g glucose x 1 mole glucose = 0.0283 mol glucose
180.16 g glucose
Step 2:
Convert mL of solution to Liters of solution
Step 3:
Solve for molarity
M = moles of solute/ liters of solution
= 0.0283 mol glucose / 0.1005 L solution
= 0.282 M
Dilutions
Adding additional solvent to dilute a more concentrated stock solution.
The total # of moles of solute does not change during a dilution (only solvent is added)
Dilution Equation:
M1V1 = M2V2
M1 = the initial molarity of the concentrated solution
V1 = the initial volume of the concentrated solution
M2 = the final molarity of the dilute solution
V2 = the final molarity of the dilute solution
Example:
What volume of 2.00 M CaCl2 stock solution would you use to make 0.50 L of 0.300 M CaCl2?
M1V1 = M2V2
M1 = 2.00 M
V1 = ?
M2 = 0.300 M
V2 = 0.50 L
2.00 M x V1 = 0.300M x 0.50L
V1 = 0.075 L
Practice Questions
1) A chemist has 250 mL of a 600 mM hydrochloric acid (HCl) solution. What volume of
water must be added to dilute it to 150 mM?
2) You have 100 mL of a 5.0 M sulfuric acid (H2SO4) solution. How many moles of
H2SO4 are present in this solution?
3) A stock solution of nitric acid (HNO3) has a concentration of 120 mM. How much of this
solution is required to prepare 250 mL of a 20 mM solution?
4) A 25 mL sample of 800 mM sodium hydroxide (NaOH) is diluted to 250 mL. What is the
final concentration of the solution in mM?
5) You mix 150 mL of a 3.0 M potassium chloride (KCl) solution with 100 mL of a 1.5 M
sodium chloride (NaCl) solution. How many moles of chloride ions are present in the
final solution?
6) A laboratory requires 1.2 L of a 200 mM calcium nitrate (Ca(NO3)2) solution. How
many moles of Ca(NO3)2 are needed?
7) A biochemist needs to prepare 750 mL of a 100 mM glucose (C6H12O6) solution from a
1.5 M stock solution. What volume of the stock solution is needed?
8) A 400 mL solution of 750 mM aluminum sulfate (Al2(SO4)3) is diluted to 1.2 L. What is
the new molarity in mM?
9) How much 18 M sulfuric acid (H2SO4) must be used to prepare 500 mL of a 300 mM
solution?
10) A 50 mL solution of 10 M acetic acid (CH3COOH) is diluted to 500 mL. How many
moles of CH3COOH are present in the final solution?
