BCHM 270 Study Guide - Fall 2018, Comprehensive Midterm Notes - Protein, Peptide, Nucleophile
12 Oct 2018
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Department
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BCHM 270
MIDTERM EXAM
STUDY GUIDE
Fall 2018
BCHM 270: MODULE 0 CHEMISTRY REVIEW
CHEMICAL SYMBOLS
• Alkanes: hydrocarbons (e.g. CH4)
• Alkenes: double bonds
• R- or R-groups: any group in which a carbon or hydrogen is attached to the rest of the molecule (side chain in amino acids)
• Aromatic compounds: benzene ring structures
• Alcohols: -OH group
• Amines: NH2 group
• Carbonyl: C=O, found in aldehydes, ketones and carboxylic acids
• Ethers: oxygen connected by two carbons, RHC-O-CHR
CHEMICAL CHARGES
• Octet rule: atoms will gain or lose electrons to have full outer shell of 8e- (full shell = stability)
CHEMICAL BONDS
• Ionic: ions bounded by attractions of oppositely charged ions
• Covalent: atoms bound by sharing electrons
• Intermolecular forces: chemical bond that holds molecules together (important for amino acids)
pH, pKa, and BUFFERING
• Acids: protons (H+) donors. Strong acids dissociate completely into proton and weak conjugate base
o When dissolving a weak acid in water, it will only partially dissociate.
o HA eak aid ↔ H+ proto + A- (conjugate base)
• Bases: proton acceptors. Strong bases will ionize completely to release powerful proton acceptor
o When dissolving a weak base in water, it will interact with hydrogen in water
o A (weak base) + H2O ↔ HA ojugate aid + OH-
• pH: poer of hdroge; epresses free proto oetratio of gie solutio
o pH = -log[H+]; higher conc of free protons = lower the pH
o pH increases = H+ decreases (weak acids lose their protons)
• Ka: dictates the amount of weak acid that will dissociate; equilibrium constant
o Large Ka = stronger acid (will dissociate more easily) and weaker the conjugate base (base is what accepts proton
to reform the acid)
o Ka = ([H][A-])/[HA]
• pKa: strength of acids; equilibrium constant
o lower pKa = stronger acid
o pKa = -logKa
• buffers: molecules that make solutions resistant to changes in pH following the addition of strong acid or base
o used eause the doate protos or hdroide ios to sol ad keep pH osistet
o weak acids or bases can act as buffers
o HA eak aid ↔ H+ proto + A- (conjugate base)
o A (weak base) + H2O ↔ HA ojugate aid + OH- (hydroxide ion)
ENTHALPY, ENTROPY, GIBBS FREE ENERGY
• Enthalpy (H): heat that is absorbed or released under constant pressure to system or chemical reaction. Thermodynamic
quantity that equals the total heat content of system.
o H = U (internal energy) + P (pressure)*V(volume)
• Entropy (S): measures the oleule radoess or disorder ithi a sste suh as heial reatios.
o Gives idea of how energy is distributed within a system
o Gibbs free energy (G): taken into account when calculating entropy. Used to determine is reactions is
spontaneous or not. G = H - TS
SOLUTIONS, CONCENTRATIONS, IMPACT ON REACTIONS
• Molarity: number of moles of solutes per L of solution
• Molality: number of moles of solute per Kg of solvent
• Mass percent: mass of solute/ mass of whole solution x 100
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• Le Chateliers Priiple: when stress is placed on equilibrium, reactions will work to minimize the stress placed on
equilibrium (rxn will work to minimize stress in whichever direction restores the equilibrium)
• Stoichiometry: relationship btwn quantities of reactants and substrates in chemical reaction.
o Law of concervation of mass: quantities of each element should be equal to products of reactants
• Equilibrium: Keq = [B]eq/[A]eq = [reactants]/[products]
REDOX REACTIONS: TRANSFER OF ELECTRONS AND ENERGY
• REDOX (oxidation-reduction reactions): take place when electrons move btwn atoms
• Reduction: atom gains electron
• Oxidation: atom loses electron
CHEMICAL PROPERTIES OF WATER
• Hydrophilic molecules: readily dissolve in water
o Ionic molecules: negative end of water dipole will interact with positive ions and positive end will interact with
negative ions (e.g. NaCl dissolves easily in water)
• Hydrophobic nonpolar molecules (e.g. CH4): not easily dissolves in water. E.g. hydrocarbons that are aromatic, aliphatic
• Amphipathic molecules: molecules that have both hydrophilic and hydrophobic properties (e.g. phospholipids that make up
cell membrane have polar head, hydrophilic, and nonpolar tail, hydrophobic)
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