OChemmidterm#1_studyguide.pdf CHEM 120
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Chapter 10: Acids, Bases, and Salts Bronsted-Lowry Acid-base theory • Acid = proton donator (donates a H+ ion) o In water H+ ions are not in a free sate in stead they are bond to water molecules (H2O) and form a H3O+ molecule § A form of coordinate covalent bonding • Base = proton acceptor (accepts a H+ ion) • The acceptance and donating of H+ ions are complementary; one will only occur with the other • HA (acid) + B (base) > A- + [BH]+ Conjugate acid and bases • In a reaction 100% proton transfer does not usually occur o Instead an equilibrium is reached where the rate of the forward reaction = the rate of the reverse reaction • Conjugate acid-base pair o Two chemical species that differ by one H+ ion § The acid in the acid-base pair will always have one MORE H ion and will be more positively charged • Conjugate acid is the one formed when the H+ ion is added § The base in the acid-base pair will always have one LESS H+ ion and by more negatively charged • Conjugate base is the one species that remains when the H+ ion is removed Amphiprotic substances • Def: a substance that can loose or gain a H+ ion (it can be an acid or a base in the reaction) o Needs both a H atom and a lone pair of electrons o Water is the most common example of this Acid classification • Root: protic o Mono: donates one H+ ion § Monoprotic acid • Ex: HCl and HNO3 o Di: donates 2 H+ ions § Diprotic acid • Ex: H2CO3 o tri: donates 3 H+ ions § Triprotic acid • Ex: H3PO4 o Poly: donates 2 or more H+ ions § Polyprotic acids Strengths of Acids/bases • Strong acid o Transfers 100% or nearly 100% of its protons to the water (when in solution) o Equilibrium is positioned far to the right (shifted towards the products) • Strong acids o HCl (hydrochloric acid) o HBr (hydrobromic acid) o HI (hydroiodic acid) o HNO3 (nitric acid) o HClO3 (chloric acid) o HClO4 (perchloric acid) o H2SO4 (sulfuric acid) • Strong bases o All hydroxide bonded elements § EX: • NaOH • KOH • LiOH • Ca(OH)2 • Most acids are weak acids, on the only ones listed above are considered strong acids • Weak acid o Transfers a small amount of H+ ions into the water § Usually less that 5% o Equilibrium is positioned far to the left (shifted towards reactants) Ionization constants • Def: an equilibrium constant for the reaction of a weak acid/base with water • Weak acids o HA (aq) + H2o (l) <> H3O+(aq) + A- (aq) o K (a) = [H3O+][A-]/ [HA] § […] = Molarity = concentration § Only include concentrations of aqueous solutions and gases • No liquids or solids • Weak bases o B (aq) + H20 (l) <> BH+ (aq) + OH- (aq) o K (b) = [BH+] [OH-]/[B] § […] = Molarity = concentration § Only include concentrations of aqueous solutions and gases • No liquids or solids Acid-base neutralization • Def: a reaction between an acid and a hydroxide base in which a salt and water is formed o AX + BY <> AY + BX § Ex: • HCl + KOH > H2O (water) + KCl (salt) • Water can act as both an acid and a base The pH scale • Used to describe the specific molar hydronium ion concentration in an aqueous solution • pH = -log(H3O+] o [H3O+] = 1.0 x 10^(-pH) o [H3O+] + [OH-] = 1.0 x 10^14 • 7 = neutral o 6.99 and less = acidic § Higher hydronium ions o 7.11 and higher = basic § Lower hydronium ions • 1 unit of change in pH = 10x change in the hydronium ion concentration Buffers • Def: an aqueous solution containing substance that prevents major changes in solution pH when small amounts of acid or base is added o A substance that will react with and remove acidic or basic molecules from a solution • So a buffer is the concentration ration of a weak acid and the salt of its conjugate base. o pH = pK (a) + log( [A-]/[HA] ) § more A- = pH higher than 7 § more HA+ = pH is lower than 7 Electrolytes • Def: a substance whose aqueous solutions conducts electricity o Strong electrolyte: completely/almost completely dissociates into its ions in water o Weak electrolyte: does not/hardly dissociates in water • mEQ = (1/1000) x (molecular weight/valence) o This represents the chemical activity of an electrolyte o Valence atomic – the number of valence electrons that each atom has § Positive or negative charge does not affect in the numerical value Chapter 12: Saturated Hydrocarbons Organic compounds • Def: the study of hydrocarbons o A carbon must be present for the compound to be considered organic o 107 million organic compounds Bonding characteristics of carbon atoms • Carbon needs 4 more electrons in its valence shell o This leads to the formation of 4 bonds to form an octet § 4 single bonds (4 atoms bonded) § 1 double bond and 2 single bonds (3 atoms bonded) § 2 double bonds (2 atoms) § 1 single and 1 triple (2 atoms bonded) Hydrocarbons and their derivatives • Hydrocarbon: a compound that contains ONLY hydrogen and carbon o Saturated: all carbon-carbon bonds are single bonds o Unsaturated: carbon-carbon bonds in which at least one double or triple bond is present • Hydrocarbon derivative: a compound that contains hydrogen, carbon, and one or more additional elements • Primary carbon: o Carbon atom directly bonded to one other carbon § 1 • Secondary carbon: o Bonded directly to two carbon atoms o § 2 • Tertiary carbon: o Bonded directly to 3 carbons § 3 • Quaternary carbon: o Directly oonded to 4 carbon atoms § 4 Structural formulas • Def: used to represent how the various atoms bonds are connected. o Expanded structural formula: shows all atoms in a molecule and all bonds connecting the atoms § H = C = H o Condensed structural formula: shows the grouping of atoms § CH2 o Skeletal structural formula (line-angle): shows the arrangement and bonding of carbon atoms present § Does not show the hydrogen atoms § C—C—C—C IUPAC nomenclature • Number of carbons o 1C: meth- o 2C: eth- o 3C: prop- o 4C: but- o 5C: pent- o 6C: hex- o 7C: hept- o 8C: oct- o 9C: non- o 10C: dec- Functional groups • Def: a structural feature in an organic molecule that is directly involved in most of the chemical reactions that that molecule participates in • In unsaturated hydrocarbons the double or triple bonds in the chain are considered functional groups • These functional groups are what compose organic chemistry because each functional group has certain properties and naming • Need to know functional groups!!! § Alkanes § Alkenes § Alkynes § Aromatic compounds § Alcohols and phenols • --OH § Carboxylic acids • --COOH § Amines • --CNR2 Isomers • Def: same molecular compound and same formula but different arrangement of atoms o The different arrangement = different properties o Only possible with 4 carbon chains or longer • Steps to finding all isomers o Start with the longest carbon chain o Take off one carbon and move it to a different place on the chain to create a branch § For it to be an isomer, you need to an actual unique arrangement • Change in carbon chain length • Branches placed on different carbon in the chain • Constitutional isomers o Def: differ in the connectivity of the atoms § Difference in the order in which the atoms are attached to each other • Stereoisomers o Def: same molecular and structural formula but different orientation of atoms in space § Cis-trans • Cis: same side of bonded carbon atom • Trans: opposite side of bonded carbon atom • Cyclo isomers o Same rule; can only create isomers with 4 or more carbons § Be careful with stereoisomers and number of carbons Alkanes • Saturated hydrocarbon that contains only carbon-carbon single bonds • Have ending –ane • When drawing alkanes they form a tetrahedral shape due to the 4 bonds created to each carbon atom o Bond angle: 109.5 degrees Acyclic • Def: a saturated chain of hydrocarbon that does not form a circle contains only carbon-carbon single bonds • General chemical formula rule: o C (n) + H (2n+2) Cyclic • Def: saturated chain of hydrocarbons that forms a ring • General formula: o C (n) + H (2n) § Always have 2 less hydrogen’s then its non cyclic counter molecule Conformation • Because alkanes are made of only carbon-carbon single bonds they have the unique property of being able to rotate because of the movability of that single bond Nomenclature for Alkanes (steps to take) 1. Identify the longest chain a. Name chain (how many carbons does it have?) 2. Number the carbons in the chain starting on the end closest to the substituents 3. Locate and name substituent groups a. If there are multiple substituents that are the in the same form indicate that with a di-, tri-, tetra-, penta- 4. If multiple substituents of different forms are present follow steps 2 and 3 then arrange the name in alphabetical order based on the first letter of the substituent group • Formalities o Commas (,) separate numbers o Hyphen (-) separates numbers from words Naming cyclo-alkanes • Same as non ringed alkanes • When counting carbons o Start counting at the point that will allow substituent to be at the lowest carbon number value § If multiple substituents, put in alphabetical order Alkanes Functional groups o A group of atoms attached to the longest chain/ring o Alkyl group § Def: group of atoms that would be obtained by removing a hydrogen atom from an alkane § -- CH3: methyl § --CH2—CH3: ethyl § --CH2—CH2—CH3: propyl § ---CH2—CH2—CH2—CH3: butyl § etc… • Halogenated Alkanes o Treated as substituents § F: flouro- § Cl: chloro- § Br: bromo- § I: iodo- o Name in alphabetical order o Considered equal rank with other substituents (alkyl group) Physical properties (cyclic and acyclic) • Insoluble in water o Non-polar substances • Density that are lower that water o .6g/mL - .8g/mL • Boiling point o Cyclic alkanes have higher boiling points then branched/un branched chains o Boiling point temperature increases with the increase in carbon chain § 1-4 carbon = gas at room temperature o Branching lowers the boiling point o Halogenated alkanes have generally higher boiling points Chemical properties (cyclic and acyclic) • The least reactive organic compound • Combustion reaction o Products: H2O + CO2 + heat energy o Light or heat is needed for reaction to occur • Halogenation reaction o Mostly Cl2 or Br2 o One or more halogen is incorporated into the molecule o Heat or light is needed • Substitution reaction o Part of a small reacting molecule replaces an atom or a group of atoms on a hydrocarbon § R—H + X2 > R—X + H—X • X = halogen • R—H = alkane Chapter 13: Unsaturated Hydrocarbons Unsaturated Hydrocarbons • Def: a hydrocarbon that contains at least one double or triple bond in the carbon-carbon chain o This causes the chain to bend a bit and not be in the same shape because of the bond strength. • Same physical properties but different chemical properties than alkanes o Chemically more reactive § The double/triple bonds are where the reactions site occurs Functional groups of unsaturated hydrocarbons o Alkenes: carbon-carbon double bond o Alkynes: carbon-carbon triple bond o Aromatic hydrocarbons: six member carbon ring Alkenes • Contains one or more carbon-carbon double bond • General formula o One double bond: C(n)H(2n) § EX: CH2 = CH2 (ethane) • The atoms bonded in the double bond form a trigonal planar shape • Atoms not involved in the double bond form a tetrahedral shape Cycloalkenes • General formula o One double bond: C(n)H(2n-2) • Naming of multiple double bonds o 2 double or more than 3: -dienes o 3 double bonds: -trienes o Not common to have multiple double bonds Nomenclature for alkenes • Find the longest carbon chain o Must contain the double bond • Name the carbons starting from the end closest to the double bond • Number what carbon the double bond takes place on o Make sure to label all double bonds if multiple ones occur and which carbons they start on Isomers for Alkenes • Same process as for alkanes = skeletal isomer formation o Different carbon-atom arrangement and hydrogen-atom arrangement • Positional isomers = moving the carbon-carbon double bond o Has the same carbon-atom arrangement • Cis-trans isomers o Redraw the molecule to emphasize the carbon-carbon double bond o Will occur if the carbon-carbon double bond has 2 different groups attached to it o Cant have identical groups attached to it § This will not allow for the bonds to break and form an isomer Alkenes substituent groups • Called a Alkenyl group • Def: non cyclic hydrocarbon substituent in which a carbon-carbon double bond is present • Most common o Methylidene (methylene) § CH2 = o Ethenyl (vinyl) § CH2 = CH— o 2-propenyl (allyl) § CH2 = CH—CH2— Physical properties of alkenes and cycloalkenes • Insoluble in water o Non polar • Lower density than water o Similar properties to alkanes • Lower melting point than alkanes even with the same number of carbon atoms • Phase state o 1-4 carbons, gas at room temp o 5-17 carbons, liquid and room temp o 17 and more carbons, solid at room temp Chemical reactions for Alkenes • Symmetrical reaction: 2 identical atoms/group of atoms are added to the carbons • unsymmetrical reaction: 2 non identical atoms/group of atoms are added to the carbons • Addition reaction o C=C + A—B > A—C—C—B § The double bond is broken § A and B break apart and separately attach themselves to each of the carbons • Hydrogenation reaction o Symmetrical reaction o C=C + H2 > H—C—C—H § Ni or Pt, heat, and pressure is needed for the reaction to occur § Alkane is formed from an alkene • Halogenation reaction o Symmetrical reaction o C=C + X2 > X—C—C—X o Most common halogens are Chlorine (Cl) and Bromine (Br) o • Hydro halogenation reaction o Unsymmetrical reaction o C=C +XY > X—C—C—Y • Hydration reaction o Unsymmetrical reaction o C=C + H—OH > H—C—C—OH § H2SO4 is needed for this reaction to occur o Markovnikov’s rule: § The hydrogen atom will attach to the unsaturated carbon atom that already as the most hydrogen atoms attached to it Polymerization of Alkenes • Polymer: a large molecule formed by the repetitive bonding together of many smaller molecules o Copolymers: polymer where 2 or more monomers are present • Monomer: the small molecule that is the structural repeating unit in a polymer • Alkenes undergo an addition reaction with one another to form carbon-carbon single bonds o Specific catalysts are needed for the reaction to occur • Degree of polymerization = Molar mass of polymer/ molar mass of monomer Alkynes • Def: has at least one carbon-carbon triple bond • Ending: o –alkyne • Always linear in shape Naming • Same exact method as alkenes but with the ending of –yne not –ene Isomers • Because it is linear in shape you cant have a cis-trans isomer • Constitutional and positional isomers are possible Physical and chemical properties of Alkynes • Insoluble in water (generally) o Soluble in organic solvents • Density lower than water • Boiling points increases with molecular mass • Like alkanes and alkenes, alkynes are very flammable and readily undergo combustion o When undergoing an reaction it takes 2 molecule conversions § 1 reaction leads to a molecule with a double bond § 2 reaction leads to a molecule with single bonds Aromatic hydrocarbons • Def: unsaturated cyclic hydrocarbon that does not readily undergo addition reactions o This reaction behavior is very different from alkenes and alkynes • Benzene o 6 carbon cyclic chain with 3 double bonds o Has a delocalized bond and 3 single bonds § A covalent bond in which electrons are shared among more than two atoms Nomenclature • As a substituent o Phenyl- o Used when a more complicated chain is attached to the ring • One substituent o Tolene: benzene ring with a methyl group o o No need to number when the group is because it is assumed that the functional group is attached to the first carbon • EXCEPTION o When a benzene ring has 2 methyl groups it changes everything… § -xylene • 2 substituent o 3 structural isomers (same concept for –xylene) • carbon 1, 2 o ortho- • carbon 1, 3 o meta- • carbon 1, 4 o para- Properties o Same physical properties as other hydrocarbons o Liquid at room temperature Chemical reactions o Heptane > toluene o Requires high temperature and a catalyst o Alkylation o Benzene + R—Cl > benzene with R group + HCl § ALCL3 needed for reaction to occur o Halogenation o One of the hydrogen atoms on the ring is replaced with a halogen (Cl or Br) o Benzene + Br2 or Cl2 > benzene with (Cl or Br) on it with H(Br or Cl) § FeBr2 or FeCl2 is needed for the reaction to occur o Free response problems (idea/tips + tricks) 1. Given name and draw structure a. Practice!!!! b. All the steps/rules are in the notes above 2. Buffer calculation a. pH = pK (a) + log( [A-]/[HA] ) 3. Complete reaction a. Addition, substitution, hydration, halogenation, hydro0halogentation, etc.. i. Memorize what is needed to make this reaction occur (heat? Energy? Catalyst?) 4. Isomers a. Constitutional isomers i. Def: differ in the connectivity of the atoms 1. Difference in the order in which the atoms are attached to each other b. Stereoisomers i. Def: same molecular and structural formula but different orientation of atoms in space c. Cis-trans i. Cis: same side of bonded carbon atom ii. Trans: opposite side of bonded carbon atom d. Cyclo isomers i. Same rule; can only create isomers with 4 or more carbons 1. Be careful with stereoisomers and number of carbons e. 5. Ch10 calculation problem pH = -log(H3O+] i. [H3O+] = 1.0 x 10^(-pH) ii. [H3O+] + [OH-] = 1.0 x 10^14
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