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Section 1- Compounds in Aqueous Solutions
• dissociation is the separation of ions that occurs when an ionic compound dissolves
– see sample problem A on page 436
– do practice problem #1 on page 436
Solubitity
• precipitation reactions occur when combinations of ions in a solution have an extremely low solubility and a precipitate forms
– see table 1 on page 437 of the textbook for general solubility guidelines
Net Ionic Equations
• An ionic equation lists all of the ions in the solutions of both the reactants and the products.
• A net ionic equation includes ONLY those compounds and ions that undergo a chemical change (usually the formation of a precipitate) in a reaction in an aqueous solution.
• Spectator ions are ions that do not take part in a chemical reaction and are found in solution both before and after the reaction.
Ionic Equations
• An example of an ionic equation.Na+ +
(aq)(aq) + Cl-(aq) + Ag+
(aq) + NO3-
(aq)
Na+ (aq) + NO3
- (aq) + AgCl (ppt)
• By removing the spectator ions (in italics), we end up with the following net ionic equation.
Ag+ (aq) + Cl- (aq) AgCl (ppt)
Do problems #1, 2, 3, & 4 on page 440 of the text.
Terms referring to solutions
• ionization occurs when ions are formed from solute molecules by the action of the solvent HCl (dissolved in H2O) H+ + Cl-
• The hydronium ion ( H3O+ ) forms when a H+ ion combines with a water molecule. This is the ion commonly associated with acids.
Terms
• A strong electrolyte is any compound whose dilute aqueous solutions conduct electricity well due to all or almost all of the dissolved compound forming ions.
• A weak electrolyte is any compound whose dilute solutions conduct electricity poorly due to only small amounts of the dissolved compound forming ions.
– Do section review questions #1 & 2 on page 443.
Historical Chemistry
• Read the Historical Chemistry feature on “The Riddle of Electrolysis”.
• Answer the two questions at the end of the feature.
• What role might electrolysis play in the production of fuel for hydrogen fuel cells?
Section 2-Colligative Properties
• Colligative properties are properties that depend on the concentration of solute particles, not their identity.
• A nonvolatile substance is one that has little tendency to become a gas under its existing conditions.
Colligative Properties
The freezing-point depression ( Δtf ) is the difference between the freezing points of the pure solvent and a solution of a nonelectrolyte in that solvent.
• is directly proportional to the molal concentration of the solution
• The molal freezing-point constant (Kf ) is the amount the freezing point of a 1.0 molal solution is depressed = -1.86°C/m
Δtf = Kfm
Colligative Properties
• boiling-point elevation ( Δtb ) is the difference between the boiling points of a pure solvent and a nonelectrolyte solution of that solvent.
• molal boiling-point constant ( Kb ) is the boiling point elevation of a solvent in a 1.0 molal solution of a nonvolatile, nonelectrolyte solute
Kb = 0.51°C/m
Do problems #1-4 on page 451.
Osmosis
• semipermeable membrane allows the passage of some particles while blocking the passage of others
• osmosis is the movement of solvent through a semipermeable membrane from the side of lower solute concentration to the side of higher concentration.
• osmotic pressure is the external pressure that must be applied to stop osmosis
• ***Read Chemistry in Action on page 453.
Electrolytes & Colligative Properties
• Because electrolytes dissolve in aqueous solution to produce more than one ion per molecule, electrolytes produce colligative properties that are almost equal to the molality of the dissolved ions.
1 mole NaCl 1 mole Na+ + 1 mole Cl- = 2 moles of ions
Do section Review problems #1, 3, & 5 on page 456.
Chemistry Chapter 13 Test Review
• multiple choice (20)– relationship of moles of ions to molecules– recognize net ionic equations– definition of precipitation reaction– use solubility guidelines to identify precipitates– definitions of dissociation & ionization– the hydronium ion formula & its anions– definitions of weak & strong electrolytes– colligative properties– how nonelectrolytes, electrolytes, and nonvolatile solutes affect
colligative properties– calculate molality using freezing point depression & molal
freezing point constant