Solution Composition: 15.2 Homework: Page 555, #12a-c, 13ab, 18, 19, 20, 21a-d Tuesday, March 4, Turn in Lab 2.Vocabulary Words (Quiz Friday) 3.Section Molarity

Vocabulary Words Solution Solvent Solute Aqueous Solution Saturated Unsaturated Supersaturated Concentrated Dilute Mass Percent Molarity Standard Solution Dilution

Molarity Mass percent describes the amount of solution in terms of mass More convenient to measure volume of a solution Chemists describe the concentration of a solution

Mass Percent

Example A solution is prepared by mixing 1.00 g or ethanol, C 2 H 5 OH, with g of water. Calculate the mass percent of ethanol in this solution = 0.990% C 2 H 5 OH

Example – Practice Problem 15.1, page 529 A 135 g sample of seawater is evaporated to dryness, leaving 4.73 of solid residue (the salts formerly dissolved in the seawater). Calculate the mass percent of solute present in the original seawater. = 3.5% salt

Molarity/Concentration Concentration: amount of solute in a given volume of solution Common expression is Molarity (M) Molarity: number of moles of solute per volume of solution in liters Molarity 

Solution Concentration Molarity – What is the molarity of a 1 L solution containing 6 moles of sugar? What is the molarity if the 6 moles of sugar is dissolved in only 500mL of solution?

Example Add 11.5 g NaOH to 1.5 L of water. What is the molarity?

Example Add 1.56 g HCl to 26.8 mL solution. What is the molarity?

Practice Problem – Exercise 15.1 p. 529 How many grams of formaldehyde (HCHO) must be used to prepare 2.5 L of 12.3 M formalin?

What is in solution? The concentration is written in terms of the form of the solute before it dissolves A 1.0 M NaCl means the solution was prepared by dissolving 1.0 mol of solid NaCl in enough water to make 1.0 L of solution Now, it doesn’t have 1.0 mol of NaCl units- has dissolved 1 M Na + and 1 M Cl -

Solution Concentration Standard Solution – when the concentration is accurately known. Volumetric flask