Stock Solutions Different experiments require solutions of various different molarities. It would not be practical to have multiple bottles of each type of solution for each different molarity needed. Concentrated (lots of moles per volume) stock solutions are stored for use in experiments. These solutions are diluted to the desired concentration as needed.

Dilution Dilution: The process of adding more solvent to a solution – Our aqueous solution are diluted by adding more water IMPORTANT: ***Only more water is added during a dilution!!! The amount of solute (number of moles) stays the same! *** Amount(moles) = sameVolume(Liters) = changes

Dilution—decrease in concentration M = moles of solute volume (L) DECREASES Stays the SAME! INCREASES (We’re adding water!)

Dilution Example How would you prepare 0.500L of 1.00M acetic acid from a 17.5M stock solution? – How many moles of acetic acid are required? L solution x 1.00 mol HC 2 H 3 O 2 = mol HC 2 H 3 O 2 L solution – What volume of the stock solution contains moles of HC 2 H 3 O 2 ? V x 17.5 mol HC 2 H 3 O 2 = mol HC 2 H 3 O 2 L solution V = L = 28.6mL of stock solution diluted to 500mL Don’t forget! M = mol ! L

17.5M HC 2 H 3 O mL 500mL 28.6 mL 500mL Add WATER to 500 mL mark 1.00M HC 2 H 3 O 2

Let’s make those calculations easier… Since the number of moles stays the same, we can simply write: M 1 X V 1 = moles of solute = M 2 X V 2 M 1 X V 1 = M 2 X V 2