exam 5; acids and bases Flashcards by Bella Willis

arrhenius acid/base definition

acid: increase [H+] in water
base: increase [OH-] in water

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bronsted lowry definition

acid: donates proton (H+)
base: accepts proton (H+)
-aqueous solution proton transfer

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lewis definition

acid: accepts share in lone pair of e-
base: donates share in lone pair of e-
*every B-L acid/base is a lewis acid/base

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conjugate acid/base

-differs by one H+; post transfer of 1 proton
-the stronger the acid/base -> the weaker the conjugate

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Autoionization of water

2 water molecules ionizing each other producing H3O+ and OH-

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acid water ion conc

[H3O+] > [OH-]

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basic water ion conc

[OH-] > [H3O+]

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ka/kb and strength of acid/base

Ka/Kb > 1: strong acid/ base
1> K > 10^-14 : weak acid/base

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autoionization of water constant;
Ka , HA + Kb, A- = Kw ( sum of conjugate pair)

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gibbs free energy and Ka

the more negative the delta G -> increased ka (stronger acid)
*strong acid less stable/ higher energy than its conjugate base (weaker)

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bond strength and Ka

stronger the H-A bond, the more able the HA molecule -> weaker/ less acidic

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electronegativity and acidity

excess e- from transfer more stable on more electronegative atoms, because greater bond polarization favors dissociation

*periodic trend: acid strength of binary hydrides increases left to right

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electron delocalization and acid/ base stength

more spread/ delocalization of e- density (more resonance) -> more stable -> less dissociation (weaker acid/ base)

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inductive effect

induce a polarization in distribution of e- density in molecule; magnitude of inductive effect depends on number of electrons present and polar nature

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Oxoacids

HOXOn
*X = central atom

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Oxoacids: terminal oxygen atom

oxygens bind to the central X atom; more terminal oxygens -> stronger inductive effect > stronger acid (lose H+ easier)

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monoprotic acids

acids that only contain 1 H+ to donate (ex. HCl)

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polyprotic acids and IE

acids with multiple H+ to donate; first ionization takes place to a greater extent

**undergos stepwise induction

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percent ionization

fraction on ions that perform as an acid/base and participate in H+ transfer (dissociated into ions)

[dissociated]/[undissociated] x100

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% ionization as dissociation constant increases

also increases

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% ionization as solution is diluted

increases as solution is diluted/ lower conc

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% ionization if product ion present or added to solution

% ionization decreases

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what does a higher dissociation constant (K) mean in terms of acid strength

higher k -> more neg deltaG -> stronger acid (less stable)

what 2 things make an acid stronger

1) reactant side instability (weaker bond to H -> easier/ less energy to transfer H+)
2) product side stability (H bond to atom with high electronegativity; polarizability)

acid strength and orbital overlap

stronger acid: smaller atoms, more orbital overlap, increased e- density

acid strength and polarity

Ka increases as polarity increases -> stronger acid

Induction

reducing charge build up for - FC / spreading electron density (still polar but less so -> less stable -> strong acid)

terminal oxygen

oxygens not bonded to anything else (only central atom)

Polyprotic acids

acids that can donate more than 1 H+; happens in a stepwise sequence of deprotonation *first depreotantion >> second SO pH based on 1st dislocation only

[conjugate acid]/ [conjugate base] =

[H3O+]/ka

[conjugate base]/[conjugate acid] =

10^ (pH-pKa)

pKa > pH

acidic form of molecule dominant

pKa< pH

basic form of molecule is dominant (drug application: lower uptake/ absorption of drug)

amino acid pH

-amphiprotic: acts as acid and base - amine group: basic - carboxyl group: acidic - side chains: can be acid or basic -> determines reactivity of amino acid

amino acid pH reactivity: primary and secondary structure

amino acid chain/ amide linkages; not very pH reactive

amino acid pH reactivity: tertiary (and quantary) structure

side group interactions; pH sensitive so vulnerable to denaturing

Denaturation

proteins quaternary, tertiary and/or secondary structures changed due to external stress (heat, acidity, etc); enzymes loose catalytic ability

amino acid side chains and pH reactivty

protonated/ deprotonated side chains -> change non covalent interactions in protein

strong acid + strong base ->

neutral salt; assume rx goes to completion and is product favored

weak acid + strong base ->

basic salt; product favored basic product

weak base + strong acid ->

acidic salt; product favored acidic product

weak acid + weak base ->

pH of product depends on reactants: -if weak acid is more acidic than weak base is basic: acidic product -if weak base is more basic than weak acid is acidic: basic product side favored depends on relative strength of reactant and product side acid/ base

reaction direction favored when products are weaker than reactants

products

reaction direction favored when reactants are weaker than products

reactants

how to calculate pH: strong reactants

-assume rxn goes to completion -solve limiting reagent problem (mol) -use limiting reagent conc

how to calculate pH: excess reagents

- identify excess reagents in solution -calculate NEW conc of H+ (ka) or OH- (kb) -calculate pH based on new conc calculated

how to calculate pH: no excess strong acid/ base

-calculate new weak acid/ base conc *using ICE table

amphiprotic acid/base rxn

2 possible reactions: more favorable rxn when weaker acid/base on product side/ product favored

condensation rxn

2 molecules join together to form a larger molecule and small molecule side product (like HCl, H2O, etc) *several sequential acid-base rxn steps

condensation rxn examples

-esterification -2 identical alcohols -> symmetrical ether -2 diff alcohols -> asymmetrical ether -carboxylic acid + primary or secondary amine -> amide

hydrolysis rxn

reverse condensation rxn

buffer definition

a solution that resist pH change when an acid/base is added

buffer composition

conjugate weak acid and base pair; conc ratio: 1:10- 10:1 to best resist pH change

buffer solution graph interpretation

best buffer is where pH changes the least; where slope on pH conc graph is least steep (ideal 50/50 conc)

adding a strong acid to buffer solution

strongest base in system will react with acid to create the most product favored rxn (strongest acid + strongest base = most product favored)

Henderson Hasselbach equation

base:acid ratio= 10:1 -> pH = pKa +1 base:acid ratio= 1:10 -> pH= pKa -1 base:acid ratio= 1:1 -> pH= pKa

common ion effect

the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate.