Aqueous Solutions and Concentration

A. Definitions Solution - homogeneous mixture Solution - homogeneous mixture Solvent - present in greater amount Solute - substance being dissolved

A. Definitions Solute - KMnO 4 Solvent - H 2 O

B. Solvation Solvation – the process of dissolving Solvation – the process of dissolving solute particles are separated and pulled into solution solute particles are surrounded by solvent particles

B. Solvation Strong Electrolyte Non- Electrolyte solute exists as ions only - + salt - + sugar solute exists as molecules only - + acetic acid Weak Electrolyte solute exists as ions and molecules DISSOCIATIONIONIZATION View animation online.animation

B. Solvation Dissociation Dissociation separation of an ionic solid into aqueous ions separation of an ionic solid into aqueous ions NaCl(s)  Na + (aq) + Cl – (aq)

B. Solvation Ionization Ionization breaking apart of some polar molecules into aqueous ions breaking apart of some polar molecules into aqueous ions HNO 3 (aq) + H 2 O(l)  H 3 O + (aq) + NO 3 – (aq)

B. Solvation Molecular Solvation Molecular Solvation molecules stay intact molecules stay intact C 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq)

B. Solvation NONPOLAR POLAR “Like Dissolves Like”

B. Solvation Soap/Detergent Soap/Detergent polar “head” with long nonpolar “tail” polar “head” with long nonpolar “tail” dissolves nonpolar grease in polar water dissolves nonpolar grease in polar water

A. Concentration The amount of solute in a solution. The amount of solute in a solution. Describing Concentration Describing Concentration % by mass - medicated creams % by mass - medicated creams % by volume - rubbing alcohol % by volume - rubbing alcohol ppm, ppb - water contaminants ppm, ppb - water contaminants molarity - used by chemists molarity - used by chemists molality - used by chemists molality - used by chemists

B. Molality mass of solvent only 1 kg water = 1 L water

B. Molality How many grams of NaCl are req’d to make a 1.54m solution using kg of water? How many grams of NaCl are req’d to make a 1.54m solution using kg of water? kg water 1.54 mol NaCl 1 kg water = 45.0 g NaCl g NaCl 1 mol NaCl

B. Molality Find the molality of a solution containing 75 g of MgCl 2 in 250 mL of water. Find the molality of a solution containing 75 g of MgCl 2 in 250 mL of water. 75 g MgCl 2 1 mol MgCl g MgCl 2 = 3.2 m MgCl kg water

C. Dilution Preparation of a desired solution by adding water to a concentrate. Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same. Moles of solute remain the same.

C. Dilution What volume of 15.8M HNO 3 is required to make 250 mL of a 6.0M solution? What volume of 15.8M HNO 3 is required to make 250 mL of a 6.0M solution? GIVEN: M 1 = 15.8M V 1 = ? M 2 = 6.0M V 2 = 250 mL WORK: M 1 V 1 = M 2 V 2 (15.8M) V 1 = (6.0M)(250mL) V 1 = 95 mL of 15.8M HNO 3

D. Molarity Molarity is the most important unit of concentration. Molarity is the most important unit of concentration. Molarity = moles of solute Molarity = moles of solute liters of solution liters of solution Symbol for Molarity is M.

Example: A solution contains 23 g of NH 4 Cl per 145 mL solution. What is its molarity?