Dilutions

1. Dilutions

2. 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.

3. 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) = same Volume(Liters) = changes

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

5. 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? 0.500 L solution x 1.00 mol HC2H3O2 = 0.500 mol HC2H3O2 L solution • What volume of the stock solution contains 0.500 moles of HC2H3O2? V x 17.5 mol HC2H3O2 = 0.500 mol HC2H3O2 L solution V = 0.0286 L = 28.6mL of stock solution diluted to 500mL Don’t forget! M = mol ! L

6. 28.6 mL Add WATER to 500 mL mark 17.5M HC2H3O2 500mL 500mL 500mL 28.6 mL 1.00M HC2H3O2

7. Let’s make those calculations easier… • Since the number of moles stays the same, we can simply write: M1 X V1 = moles of solute = M2 X V2 M1 X V1 = M2 X V2