Chem 112 exam 2
Chem 112 exam 2 CHEM 112000
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This 6 page Study Guide was uploaded by Olivia Lee on Monday February 29, 2016. The Study Guide belongs to CHEM 112000 at Purdue University taught by Abu-Omar in Winter 2016. Since its upload, it has received 73 views. For similar materials see Chemistry in Chemistry at Purdue University.
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Date Created: 02/29/16
nd CHEM 112 1 Edition Exam # 2 Study Guide Chapters 11-13 CHEM 112 Study Guide 2 CHAPTER 13 CHEM 112 -Arrhenius model of acids and bases: acids in an aqueous solution produce hydroxide (H+) ions, and base produces hydroxide ions (OH-) -hydronium ion: H3O+ -Bronsted Lowry Theory: acid is any substance that can donate an H+ ion to another substance; it defines a base as any substance that can accept an H+ ion from another substance. -Conjugate acid-base pairs: the products that forms as a result of losing an H+ ion Example: H2PO4- becomes HPO4(^2-) -amphoteric substance: a substance that can act as either an acid or base\ -weak acids: any acid that is not a strong acid is a weak acid. If it does not completely dissolve in water, then it is a weak acid. Equilibrium arrows are used when describing a weak acid. -weak bases: does not completely ionize when dissolved in water Degree of ionization: the percentage of molecules that ionize *ions with a greater degree have a great equilibrium constant Ex: 1.8 E -5 versus 6.2 E -10 the 1.8 is a stronger acid because it has a higher constant (vice versa for bases, we want the smallest number) Ka value describes the equilibrium that forms when an acid dissolves in water Polyprotic acid: an acid that can donate more than one H+ ion In an acidic solution, the H3O+ ion concentration is greater, OH- is greater in a basic solution. In a neutral solution, there is an equal concentration of H3O+ and OH- ions. Self ionization: water reacts with itself and one H+ is transferred Ion-product constant of water: 1.0E-14 and water has a pH of 7 or 1.0E-7 When calculating concentration: put 1.0E-14 on top and divide by the value given Given the concentration: 5.0E-4 use: -log(5.0E-4) pH=3.30 When just given a base: 1. Divide from 1.0E-14 2. Then do log procedure pOH is adding it up to 14 buffer: combination of a weak acid and a strong base in about equal concentrations: buffer system works if there is enough acid and conjugate base in the system to react with all the added H3O+ or OH- strong acids cannot be a part of the buffer system CHAPTER 12 CHEM 112 12.1 Reaction Rate: how fast a reaction occurs 1. temperature (milk spoils when left out of the fridge) 2. reactant concentration/surface area (metal granulaes react faster with air) 3. catalysts (enzymes can act as catalysts) 12.2 Collision Theory: in order for a reaction to occur, reactant molecules must collide in the proper orientation and with sufficient energy -endothermic reactions: the reactants are lower in energy than the products (energy is absorbed) -exothermic reactions: the products are lower in energy than the reactants (energy is released) Activation energy: minimum amount of energy needed to overcome this energy barrier (when comparing two similar reactions at the same temperature, the reaction with the lower activation energy minimum amount of energy needed to overcome this energy barrier (when comparing two similar reactions at the same temperature, the reaction with the lower activation energy is the faster reaction) Activated complex: a short lived unstable high-energy chemical species that must be achieved before products form 12.3 Conditions that affect reaction rates: 1. Concentration and Surface Area: an increase in concentration of one or more reactants increases the number of reactions per unit volume 2. Temperature: higher temperature means higher kinetic energy which causes a higher fraction ofcollisions Example: increase rate of reaction of 5.0 g Mg metal strip in a 0.10 M HCl solution: how can she increase the rate of this reaction? -increase the concentration of the HCl to 0.20 M -increase the surface area of magnesium metal by cutting it into smaller strips -heat the reactant mixture on a hot plate: but use caution because hydrogen is flammable 3. Catalysts: alter tge pathway in which a reaction occurs without itself being consumed in the reaction -enzyme: a molecule that catalyzes specific reactions within living organisms, life would be to slow as a results of the very low temperatures Catalysts occur in the reaction and product side after the equation is simplified. Intermediates form temporarily during the reaction (product of eq 1 and reactant of eq 2) 12.4 Chemical Equilibrium: a state reached where there is no change in the concentration of reactants and products (reversible reactions) 12.5 Equilibrium Constant: If K(eq) > 1 lies to the right (products) If k(eq)<1 lies to the left (reactants favored) Heterogenous equilibrium: a reaction that involves more than one physical state -do not include liquids or solids when writing the equilibrium expression 12.6 Le Chatelier’s principle: if equilibrium is disrupted it shifts to establish a new equilibrium General Add reactant Add product Remove Remove reaction reactant product A + B = C + D Shift right Shift left Shift left Shift right - Increasing the volume allows the concentration of a gas to decrease. Count the number of moles!! Watch out! Temperature: Type of reaction Equation Increase temp Decrease temp Endothermic Heat + A + B = C Shift right Shift left + D exothermic A +B= C + D + Shift left Shift right heat Chapter 11 Chem 112 11.1 the composition of solutions -solution: homogenous mixture with uniform composition throughout -solute: he substance being dissolved -solvent: the substance doing the dissolving -aqueous solution: when the solvent is water -solubility: how readily a solvent will dissolve -miscible: can be mixed in any proportion to give a homogeneous solution 11.2 The solution process -ion-dipole force: force of attraction between an ion and a polar molecule -hydration: a solute particle is surrounded by solvent water molecules in a solution When an ionic compound dissolves in the water the process can be summarized as: Ionic bonds break the solute, the hydrogen bonds between the water molecules break, ion-dipole forces form between ions an water molecules -entropy: measure of tendency for matter to become disordered or random in its distribution 11.3 Factors that affect solubility: -structure: -‘like dissolves like’ Solute Solvent: Polar Solvent: Nonpolar Ionic Soluable Insoluable Polar Soluable Insoluable Nonpolar insoluable soluable Temperature: the solubility of ionic solids in water increases with increasing temperature Pressure: the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid 11.4 Measuring concentrations of solutions: -concentration: relative amounts of the solute and solvent that make up the solution -solubility: the ratio that identifies th maximum amount of solute that will dissolve in a particular solvent to form a stable solution under specified conditions -saturated contains maximum amount of solute (supersaturated is over the maximum amount) percent by mass = grams of solute/grams of solution (100) percent by volume = volume of solute/volume of solution (100) Molality = moles of solute/liters of solution Molality = moles of solute/kilograms of solvent Parts per million E6 parts per billion E7 Titration: process of determining the concentration of one substance in solution by reacting it with a solution of another substance that has a known concentration 11.6 Colligative Properties: dependent on the number of solute particles present Osmotic pressure: process in which solute particles diffuse through a barrier that does not allow the passage of solute particles
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