Chapter 3&4 review notes(weekly bundle)
Chapter 3&4 review notes(weekly bundle) Chem 142
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This 14 page Bundle was uploaded by Jessie Yuan on Sunday November 15, 2015. The Bundle belongs to Chem 142 at University of Washington taught by Dr. Li Xiaosong in Fall 2015. Since its upload, it has received 54 views. For similar materials see General chemistry in Chemistry at University of Washington.
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Date Created: 11/15/15
CHAPTER 3amp4 REVIEW NOTES WEEKLY BUNDLE JESSIE YUAN U WASHINGTON STOICHIOMETRY The Atomic Mass Unit amu 0 Defined as 112 the mass of a carbon12 atom O The masses of all other atoms are given relative to this standard 0 The atomic masses you find on the periodic table are a weighted average of the masses of each isotope of that element Atomic Mass The Atomic Mass aka Atomic Weight or Average Atomic Mass is the average of the atomic masses of all of the element39s isotopes weighted by isotopic abundance Don t confuse quotAtomic Mass with the mass of one atom Counting by Weighing 0 Chemical reactions occur at the microscopic level between individual molecules andor atoms O In the lab we measure substances in terms of grams or millilitersthese are macroscopic measurements 0 The number of molecules in 1 g of water will be different than the number of molecules in 1 g of glucose because these molecules have different masses 0 We need a way to convert between the microscopic and macroscopic descriptions Percent Composition of Compounds 0 Sometimes it is helpful or necessary to know a compound s composition in terms of the masses of its elements 0 We can also deduce a molecular formula based on a given percent composition 0 Mass Fraction and Mass Mass fraction mass of one component element particle etctota mass of molecule box of marbles etc Empirical and Molecular Formulas 0 Empirical Formula The simplest formula for a compound that agrees with the elemental analysis The smallest set of whole numbers of atoms 0 Molecular Formula The formula of the compound as it really exists It must be a multiple of the empirical formula Chemical Equations 0 Chemistry is the study of the rearrangement of matter due to the flow of energy O In a chemical reaction some bonds are broken and others are formed resulting in a reorganization of the atoms 0 Atoms are neither created or destroyed in a chemical reaction Law of Conservation of Mass Reactants and products must occur in numbers that give the same number of each type of atom on both sides of the arrow Formulas of Elements and Compounds 0 The name or chemical formula of a compound gives you information about the relative number of atoms in the compound sodium chloride NaCl copper nitrate CuNO32 carbon tetrachloride CC4 O The formula of most elements particularly metals is simply the element symbol tungsten W calcium Ca boron B carbon C O Elemental forms of nonmetals are often found as molecules H2 N2 02 F2 Cl2 Br2 2 58 C60 P4 How to Balance Equations Mass Balance or Atom Balance same number of each element on each side of the equation 1 start with largestmost complicated molecule 2 progress to other elements leaving lone elements for last 3 make all whole numbers 4 recheck atom balance Mole Ratios We can use a balanced chemical equation to predict the number of moles of products that a given number of moles of reactants will produce Theoretical vs Actual Yield 1 The theoretical yield of a reaction is the amount of product that would be formed under ideal reaction conditions in which starting materials are completely consumed up to the LR This is a calculated number i The actual yield is the amount of product that is actually produced in real life in the lab 1 The actual yield is always less than the theoretical yield because LR starting materials may not be completely consumed side reactions may occur the reverse reaction may occur there may be loss of product during purification steps Percent Yield A comparison of How much product we actually produced to how much product we could theoretically produce gives us the percent yield of a chemical reaction Solutes Solvents and Solutions Solute 1 Substance being dissolved mixed diluted 1 Example compounds extracted from coffee grounds sugar milk Solvent 1 Substance doing the dissolving mixing dilution 1 Example water Solution 1 Final combination of dissolution mixing and dilution 1 Example morning coffee Water as a Solvent 1 Water is an important solvent dissolves many substances 0 I II i Aqueous means a solutIon In which water IS the solvent 1 Water is a POLAR molecule Polar and Nonpolar Solutes 1 Water dissolves some nonionic substances if they are polar ethanolwater i Ethanol molecules are polar contain directional OH bond Ionic Solutes 1 Polar water molecules dissolve ionic compounds salts i quotHydrationquot breaks ionic compounds into anions and cations 1 Water dissolves different ionic compounds to different degrees more in Ch 8 The Role of Water as a Solvent Dissolution of Ionic Compounds Electrical conductivity the flow of electricity in a solution indicates the presence of ions in solution Electrolyte a substance that conducts a current when dissolved in water ons become solvatedhydrated they are surrounded by water molecules These ions are labeled quotaqueousquot they are free to move throughout the solution and conduct electricity Electrolytes and NonElectrolytes i If a solution conducts electricity it contains ions 1 A solution that contains many ions is a strong electrolyte i A solution that contains only a few ions is a weak electrolyte i A solution that contains no ions is a nonelectrolyte Strong Electrolytes strong electrolytes substances that are good conductors of electricity 1 These substances break up to produce many ions in water 1 many ions present to move electronsconduct electricity strong electrolyte Weak Electrolytes weak electrolytes substances that are weakpoor conductors of electricity 1 These substances mostly remain intact as compounds producing very few ions in water i only a few ions present to move electronsconduct electricity weak electrolyte Nonelectrolytes nonelectrolytes substances that cannot conduct electricity 1 These molecules never break down into ions 1 They always remain intact as neutral molecules that have no charge no ions to move electronsconduct electricity Dissolving compounds in water 1 When an ionic compound is dissolved in water i ons are quothydratedquot i Separated from their solid crystal 1 Become individual ions in solution Concentration 1 Many chemical reactions take place quotin solution 1 Still need to know amounts of reactants and products 1 How do we make solutions of known concentrations i We measure concentration in terms of moles per volume Molarity M moles of soluteliters of solution Dilution i The number of moles n of solute stays the sameonly the volume of solution V changes n MV 1 We can formalize this relationship M1V1 M2V2 n where M1 V1 molarity and volume of concentrated solution M2 V2 molarity and volume of diluted solution Types of Chemical Reactions i Precipitation Reactions 1 AcidBase Neutralization Reaction 1 OxidationReduction Redox Reactions i Further classified as Combination Decomposition Combustion Singlereplacement reactions Solubility Rules TABLE 41 Simple Rules for the Solubility of Salts in Water 1 Most nitrate NOf salts are soluble 2 Most salts containing the alkali metal ions Li Na K Cs Rb and the ammonium ion NHf are soluble 3 Most chloride bromide and iodide salts are soluble Notable exceptions are salts contain ing the ions Ag Pb and Hg 4 Most sulfate salts are soluble Notable exceptions are BaSO4 PbSO4 Hg3804 and CaSO4 5 Most hydroxide salts are only slightly soluble The important soluble hydroxides are NaOH and KOH The compounds BaOH2 SrOH2 and CaOH2 are marginally soluble 6 Most sul de 82quot carbonate COf chromate CrOf and phosphate POf salts are only slightly soluble Total and Net Ionic Equations Conventional molecular equation a bookkeeping of all species present and arranged for charge neutrality Total Ionic equation all aqueous species are split up into their component ions Net Ionic equation indicates exactly the chemical change that occurs and nothing more Selective Precipitation Some ionic compounds are soluble while others are not We can use this behavior to remove species selectively Example separating Ag from Ba2 and Fe3 Notice that selective precipitation is nothing more than an application of the solubility rules AcidBase Reactions Generally in an acidbase reaction 1 H from acid reacts with the OH from base to form water H20 1 The cation M from base combines with anion from acid X to form a salt AcidBase Rxns BronstedLowry Theory acidbase reactions are protontransfer processes 1 acid is protondonor H ion donor 1 base is proton acceptor H ion acceptor Strong and Weak Acids 1 Strong acids think quotstrong electrolyte undergo complete ionization 1 Weak acids think quotweak electrolyte undergo incomplete ionization Weak acids are like insoluble saltsthey don t like to dissociate very much OxidationReduction Redox Reactions 1 Redox Chemistry Reduction and Oxidation i Oxidation Loss of electrons 1 Reduction Gain of electrons a reduction in oxidation number Redox Reactions i In a redox reaction one species loses electrons and another species accepts those electrons i Electrons are neither created nor destroyed during the reactioncharges are conserved Oxidation Numbers or States i Oxidation number state represents the number of electrons required to produce the quoteffective charge on a species 1 Oxidation numbers states are chosen so that i charges are conserved i in ionic compounds the sum of the oxidation numbers on the atoms is the same as the charge on the whole ion the oxidation numbers of the atomsions in a species must sum to the total charge of the species OxidationReduction Redox Reactions Types of Redox Reactions 1 Combination Reaction 1 Decomposition Reaction 1 Replacement or Displacement Reaction 1 Combustion Reaction Activity Series Activity Series Relative order of elements arranged by their ability to replace cations in aqueous solution Or stated another waytheir ease of oxidation or loss of e to form a cation LigtKgtBagtSrgtCagtNagtMggtAlgtMngtZngt FegtCdgtCogtNigtSngtPbgtHgtCugtAggtAu Balancing REDOX Equations The HalfReaction Method Step 1 Write the halfreactions for the chemical equation Step 2 For each reaction balance the atoms other than 0 and H Step 3 Add H20 to balance 0 then H to balance H Step 4 Balance the charge by adding electrons The net charge of the reactants should equal the net charge of the products Step 5 Add the two halfreactions together making sure e lost equal e gained and canceling any species that appear on both sides of the reaction The reaction is now balanced in an acidic solution Step 6 If you need to balance in a basic solution first balance in acidic solution then add OH to both sides to neutralize any H present Cancel any species that appear on both sides of the reaction
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