1. Concentration Molarity

2. Nature of Solutions  Because solutions are mixtures, the composition can vary among samples  Consider barely sweet tea versus the syrupy sweet stuff that some people drink  It is important to know how much “stuff” is dissolved in solutions  We consume acids that are dilute (OJ, vinegar, lemons)  But we cannot consume more concentrated acids safely

3. Vocabulary  Concentration – amount of solute in solvent  Dilute – relatively small amount of solute dissolved  Saturated solutions may be dilute  Concentrated – relatively large amount of solute dissolved  Unsaturated solutions may be concentrated  Concentration is a measure of how much stuff IS dissolved; Solubility is a measure of how much stuff CAN dissolve  Molarity – common unit of concentration  M = moles of solute liters of solution

4. What is the concentration of 250.0mL of a solution containing 25 grams of sodium hydroxide? 1 st – change grams to moles 25g = X 40 1 X =.625 moles 2 nd plug into M formula M =.625mol.250 L M = 2.5 mol/L How much potassium chloride is needed to prepare 500.0ml of a 0.125M KCl solution? 1 st – find the # of moles of KCl in the solution.125M = X mol.500L X =.0625mol 2 nd Change moles to grams.0625mol = X g 1 74.55 X = 4.66g KCl Molar mass of NaOH 2.5M 4.66g KCl Molar mass of KCl

5. Dilutions How many milliliters of a solution of 4.00M KI is needed to prepare 250.0mL of a 0.760M KI? M 1 V 1 = M 2 V 2 4.00M x V = 0.760M x 250.00mL V = 47.5mL