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MSU CEM 142 - Exam 2 Study Guide

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Cem 142 1st Edition Exam # 2 Study GuideChemical Reactions- Involve rearrangements of atoms- Atoms are conserved- Connections between atoms change- Involve changes in location of valence electronso Responsible for chemical properties Acid-Base Reactions- Arrhenius Acid Base modelo Ignores the role of water, it is not usedH+- No such thing in aqueous solution- Very small and highly charged- Surrounded by H2O molecules (solvation shell)- **H3O+ is a better representation, assume H+ is H3O+Bronsted Lowry- Acid is the proton donor- Base is the proton acceptor- This model is limited, mostly good for proton transferso Acid-base reaction can occur without proton transfersLewis Acids and Bases- Acid is the electron pair acceptor- Base is the electron pair donoro Base initiates the reaction- Empty orbitals of available energyThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Heme- A Lewis acid-base complex- Seen in blood (hemoglobin)o Iron attaches to oxygen*Water can be both an acid and a base*Conjugates- Conjugate acids have the H+- Conjugate bases have the gained electrons- DO NOT FORGET TO PUT FORMAL CHARGESo #valence electron - # of electrons in structureHow to Spot Acids- An H+ is covalently bonded to an electronegative atom- When an acid is in water (or in any solvent), the interactions of the acid are weakened - Conjugate base is stable*The more polar =easier to remove an H+ =More acidicHow to Spot Bases- All have a lone pair of electrons available to form a new bond- Less electronegative = more willing to share their lone pairo Electronegative atoms hold onto electrons tightlyStrengths of Acids and Bases- Some acids are strongo They are fully ionized in solution - Some acids are weako They are not fully ionized in solution- If solution conducts electricity, they are ions- Acids ionized to different extents, strength depends on:1. Electronegativity2. Polarity 3. Change in enthalpy a. The higher the number of change in enthalpy, the more energy is released when dissolved*Note: - Concentrated and diluted = amount of solute and solvent- Strong and weak = refers to the particles’ strengtho You can have a concentrated solution of a weak acidBond Dissociation Energy- Bond enthalpy: the energy it takes to break the H-X (an acid) bond in the gas phase H—X  H• •Xo The higher the bond energy, the stronger the bond- Entropy change is also important- The more polar, the easier it is to pull off the H+Resonance Structures- The negative charge needs to be able to spread out on the moleculeBase Strength- Same atom, both with a lone pair, the one with a negative charge will be the stronger base- Size determines strengtho Orbital overlap Stronger acid if orbitals do not overlap- The more electronegative, the more the acid will not share electrons*Note:- Molecules with charges are more reactive than neutral moleculeso In order to get rid of the charge and make something neutralpH- Temperature dependent o Pure water with 6.8 pH at 37ºC is still neutral- Using the pH, you can find the concentration of an acid/base- Higher % ionization, stronger acido % ionization = (amount ionized / total) x 100Electrophiles and nucleophiles- Extension of Lewis acid base theory… - The nucleophile is the one that has the lone pair, the electrophile accepts the


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