Concentration

Molarity

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

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

What is the concentration of 250.0mL of a solution containing 25 grams of sodium hydroxide?

• 1st – change grams to moles 25g = X 40 1 X = .625 moles

• 2nd 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?

• 1st – find the # of moles of KCl in the solution .125M = X mol .500L X = .0625mol

• 2nd Change moles to grams .0625mol = X g 1 74.55 X = 4.66g KCl

Molar mass of NaOH

2.5M4.66g KCl

Molar mass of KCl

Dilutions

• How many milliliters of a solution of 4.00M KI is needed to prepare 250.0mL of a 0.760M KI?

• M1V1 = M2V2

• 4.00M x V = 0.760M x 250.00mL• V = 47.5mL