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THE MCAT-CHEM 2
ACIDS, BASES, BUFFERS
| Question | Answer |
|---|---|
| Arrhenius acid | produces H |
| Arrhenius base | produces OH |
| Bronsted and Lowry acid | donate H |
| Bronsted and Lowry base | accept H |
| Lewis acid | accept pair of electrons |
| Lewis base | donates pair of electrons |
| Strong acid... | weak c.b. |
| Strong base... | weak c.a. |
| Weak acid... | do NOT necessarily have strong c.b. |
| pH + pOH= | 14 |
| Strong acid / base has ______ dissociation because conjugate species is ______. | complete / stable |
| A weak acid / base has _______ dissociation because conjugate species is _____. | partial / fairly stable |
| For a strong acid/base, the conc. of H / OH produced is the same as? | original concentration of acid / base |
| Strong acid: 0.01M H = | 0.01 M of original acid |
| Relate Ka, pKA for strong acid | larger Ka, smaller pKA, stronger acid |
| Relate Kb, pKb for strong base | larger Kb, smaller pKb, stronger base |
| pH > pKa | deprotonated |
| pH < pKA | protonated |
| amphoteric vs. ampipathic | -amphoteric = act as either an acid / base -ampipathic = hydrophobic / hydrophilic |
| Why is Ka so larger for strong acids? | complete dissociation |
| Shortcut equation to determine pH for weak acid / base reagent? | pH = 1/2pKa - 1/2 log [HA] |
| Henderson - Hasselbalch Equation | pH = pKa + log (conj. base) / (conj. acid) --> use conc. or mole quantities |
| Where in graph is buffer most important? | 1/2 equivalence point |
| What characteristics for 1/2 E.P. for titration of acid with strong base? | -pH = pKa -moles acid = moles conjugate base -[acid] = 1/2[base] |
| Equivalence point | moles acid/base = moles titrant |
| In the titration of an acid with a strong base, what is the predominant species at the E.P.? | 100 % A- |
| What is a good buffer? | pH = pKa +/- 1 |
| For Haloacids, within a group, what dictates acid strength? | halogen size and bond length |
| For haloacids, within a period, what dictates acid strength? | electronegativitiy of atom |
| Why do more oxygens increase acid strength? | double bonded oxygens are EWG making electron deficient |
| Nonmetal oxide is a ____ acid. Metal oxide is a _____ base. | lewis |
| Nonmetal hydroxide is a _____ acid. Metal hydroxide is a _____ base. | bronsted and lowry |
| Calculate Normality. | acid molarity * number of protons |
| Which proton removed in a polyprotic acid is always the most acidic? | first |
| Will adding water change the pH of a buffered solution? | NO --> equally dilutes weak acid and conj. base |
| A buffer is rougly equal conc. of what? | weak acid and weak conj. base |
| The ratio of weak acid: conj. base for a buffer cannot exceed? | 10:1 (in favor of either) |
| What does a buffer create? | relatively constant pH through resisting changes caused by titration |
| the Pka of the weak acid for a buffer should be close to what? | the desired pH of the solution |
| base + acid = | salt and water |
| Strong acid + strong base, pH = | 7 |
| strong acid + weak base, pH = | < 7 |
| strong base + weak acid, pH = | > 7 |
| Does a strong acid + conj. base create a buffer? | NO |
| Buffer recipes | 1. weak acid + conj. base 2. weak base + conj. acid 3. weak acid + strong base 4. weak base + strong acid |
| All acid/base rxns produce salt. T / F | TRUE |
| Strong acid / strong base titrations are characterized by _____ graphs. | sigmoidal |
| For strong acid and strong base,w here does rapid change occur? | near E.P. |
| For strong / weak titrations, where does rapid change occur? | at the beginning |
| What is Henderson - Hasselbach equation used for? | to calculate pH for buffers |
| What does the pH of a solution depend on? | strength and concentration of the reagents |
| Strong / weak titrations are characterized by ______. | lip-o-weakeness curves |
| Does the E.P. for a strong acid / base ever change? | NO |
| What are the strong acids? | HI, HBr, HCl, HNO3, HClO4, HClO3, H2SO4 |
| What are strong bases associated with? | OH, NH2, H, O |
| ionization of water Kw = | Kw = 10^-14 |
| Formula for pH | pH = -logH |
| What does pH for pure water = ? | 7 |
| Is CH3COONa the salt of a weak acid or base? | salt of a weak acid |
| Is NH4Cl the salt of a weak acid or base? | salt of a weak base |
| pKa = | - log Ka |
| pKb = | - log Kb |
| When acid = conj. base for a buffer, what else is equal? | pH = pKa |
| When base = conj. base for a buffer, what else is equal? | pH = 14 - pKa |
| pKa + pKb = | 14 |
| When solution is low pH, indicator is in which form? | protonated |
| When solution is high pH, indicator is in which form? | deprotonated |
| At 1/2 E.P., how much of reagent has been titrated? | half |
| Going from a pH = 1 to pH = 2, means to go from 0.1 to? | 0.01 |
| What does a pH = 0 equal to? | 1 |
| What does a color change of a rxn depend on with an indicator? | pKa of indicator |
| A weaker acid needs a stronger / weaker base to abstract H? | stronger |
| A stronger acid needs a stronger/weaker base to abstract H? | weaker or stronger base can work |
| What are strong bases? | Group I / Group 2 + hydroxides |
| Do metal ligands act as lewis acids or bases? | lewis acids |
| Are all Arrhenius acids and bases also BL acids and bases? | yes |
| Generally, are hydrogens attached to carbon acidic? | GENERALLY no with acids / bases |
| Are the hydrogens on NH4+ acidic? NH3? | YES / NO |
| What creates an Arrhenius acid? | compound can lose a hydrogen and leave behind a stable compound --> react with water to produce hydronium |
| Are negative ions lewis acids or bases? | lewis bases |
| Are positive cations lewis acids or bases? | lewis acids |
| Are all Lewis acids Bronsted-Lowry? Are all BLs lewis acids? | NO / YES |
| What type of compounds are lewis acids? | cpds with leaving groups, double/triple bond, incomplete octet |
| Every dilution by a factor of 10 increases pH by? | 1 unit |
| To form a conjugate base... To form a conjugate acid... | -remove hydrogen -add hydrogen |
| Do weak acids/bases necessarily have strong conjugates? | NO |
| What is the definition of a strong acid? Weak acid? | stronger than hydronum / weaker than hydronium |
| What are the strong bases from group 2? | Ca, Sr, Ba |
| When a pH goes up by one, hydrogen ion concentration increases by? | a factor of 10 |
| Is hydride or hydroxide ion stronger base? | hydride |
| The equilibrium for autoionization of water lies to the left/right? | -left 2H2O --> H3O + OH |
| What is the pKa of distilled water? | 15.74 |
| What is the Kw for water? | 1E-14 |
| Equilibrium in an acid/base reaction will always lie on the weaker/stronger side? | weaker |
| What do you need to consider with dilute solution? | autoionization of water |
| Which cations do not form weakly acidic solutions in water? | alkali metals and alkaline earth metals |
| amphiprotic | act as acid or base |
| What kind of cation forms the strongest acidic solution? | small and greater charge cation |
| At what pH is there the most rapid change in a strong acid/strong base titration? | at E.P. |
| Does pH = 7 at the E.P. for strong/weak titrations? | no |
| What creates weak electrolytes? | compounds that do not dissociate |
| Does an acid dissociate more or less in more concentrated solutions? | less |
| Does acid strength increase or decrease with increasing concentration? | increase |
| What is a strong base? | base that is stronger than OH- |
| Are metal hydrides basic or acidic? | basic |
| Are nonmetal hydrides basic or acidic? | acidic |
| For strong acids, the concentration of dissociated H+ is the same as? | original concentration of the acid |
| What is an equivalent? | mass of acid/base necessary to produce or consume one mole of protons |
| Does adding a small amount of water to a dilute, buffered solution effect the pH? | NO |
| For haloacids, how to guage acidity? | look at electronegativity of central atom |
| How to choose indicator for titration? | pH (equivalence) = pKa(indicator) +/- 1 |
| Does a more concentrated acid have a lower or higher pH? | lower pH |
| In a BL acid/base reaction, is an H- transferred or an H+? | H+ |
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