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MCAT chemistry > chapter 7 > Flashcards

chapter 7 Flashcards

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1
Q

what is the Arrhenius definition of acid and bases?

A
  • acids dissociate in a manner that increases the concentration of protons in solution
  • the dissociation of a base increases the concentration of hydroxyide ions
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2
Q

what is the Bronsted-Lowry definition of acids and bases?

A
  • an acid is a proton donor
  • a base is a proton acceptor
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3
Q

what is the Lewis definition of acids and bases?

A
  • acids are electron acceptors
  • bases are electron donors
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4
Q

what is a compound called when it can act as both an acid or a base?

A
  • amphoteric
    • can accept or donate a proton (BL) “amphiprotic”
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5
Q

how to name acids with an oxygen:

A
  • prefix hydro, the root of the parent anion, and the suffic -ic acid
    • ex. Hydrochloric acid
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6
Q

how to name oxyacids?

A
  • for oxyanions that contain the suffix -ate, the acid uses the suffix -ic
  • if an oxyanion contains one more O atom than the corresponding “ate” ion, then the acid uses the prefix -per and the suffix “ic acid”
  • if an oxyanion contains one fewer O atoms than the corresponding “ate” ion, then the acid uses the suffix -ous acid
  • if an oxyanion contains 2 fewer oxygen atoms then the corresponding “-ate” ion, then the acid uses the prefix =hypo and suffix -ous acid
    • ClO- hypochlorite
    • ClO2- chlorite
    • ClO3- chlorate
    • ClO4- perchlorate
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7
Q

what is Kw?

A
  • the constant for the autoionization of water
    • the reaction of water molecules with each other to form ion s
      • Kw = [H3O+][OH-]
      • the value of Kw at room temperature is 1.0 x 10-14 and is temperature dependent
      • pH of 7
      • ionizes to a greater extent in warmer temperatures and less in colder temperatures
      • as long as hydronium and hydroxide concentrations are equal, the solution is neutral
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8
Q

each acid and base have their own dissociation constants respectively:

A
  • ka
  • kb
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9
Q

what does a high Ka and low ka signify?

A
  • a high Ka corresponds to an acid that dissociates more readily
  • a low ka corresponds to an acid that does not dissociate to a large degree
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10
Q

strong acids vs weak acids:

A
  • strong acids have large ka values with positive exponents
  • weak acids have small ka values with negative exponents
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11
Q

list of strong acids (7):

A
  • hydrochloric acid (HCl)
  • hydrobromic acid (HBr)
  • hydroiodic acid (HI)
  • chloric acid (ClO3)
  • perchloric acid (HClO3)
  • sulfuric acid (H2SO4)
  • nitric acid (HNO3)
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12
Q

list of strong bases:

A
  • lithium hydroxide (LiOH)
  • sodium hydroxide (NaOH)
  • potassium hydroxide (KOH)
  • cesium hydroxide (CsOH)
  • calcium hydroxide (CaOH2)
  • Strontium hydroxide (SrOH2)
  • barium hydroxide (BaOH2)
  • the conjugate base of ammonia (NH2-)
  • the hydride anion (H-)
  • methoxide (CH3O-)
  • ethoxide (CH3CH2O-)
  • tert-butoxide ((CH3)3CO-)
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13
Q

the Kb of a strong base will be?

A
  • very large
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14
Q

what are the equations to get pH from an acid or a base?

A
  • pH = -log[H+]
  • pOH = -log[OH-]
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15
Q

pKw = pH + pOH is also:

A

14 = pH + pOH

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16
Q

pKa and pKb are negative logarithms of?

A
  • ka and kb
    • ​pH = -log ka
    • pOH = -log kb
17
Q

the stronger an acid…

A
  • the weaker its conjugate base
18
Q

A buffer must contain either?

A
  • a weak acid and its conjugate base or a weak base and its conjugate acid
19
Q

the pH of a buffer solution can be calculated using the Henderon-Hasselbach equation:

A
  • pH = pKa + log [A-]/[HA]
    • when equal concentrations of acid and conjugate base are present, the “log” term drops out and pH = pKa
    • choose a buffer where the acid has a pKa close to the desired pH of the buffered solution
20
Q

what is a titration?

A
  • a titration is a technique that aims to determine the concentration of a solution of unknown molarity
    • to accomplish this, a solution of known concentration is added until an endpoint is reached (associated with colour change) and the amount of known solution (titrant) required to reach the endpoint can be used to determine the concentration of the unknown reactant (analyte)
21
Q

when does the endpoint of an acid-base titration occur?

A
  • AKA the equivalence point occurs when the original acid or base has been fully neutralized by the added base or acid
22
Q

for polyprotic acids, a complete titartion involves?

A
  • neutraliztion of multiple protons
    • polyprotic acids have amphiprotic conjugate bases
23
Q

how to calculate normality:

A
  • normality (N) = moles of equivalents / litres of solution
    • equivalents means acidic protins or hydroxide ions
24
Q

the amount of base or acid required to fully neutralize an acid or base is:

A
  • NacidVacid = NbaseVbase
    • relates the normalities and volumes of the 2 solutions
25
Q

what are indicators?

A
  • indicators are weak acids or weak bases that take on different colors depending on their protonation state
    • ex. phenolpthalein is colorless when protonated and pink when deprotonated
      • the pKa of the indicator should be as close as possible to the predicted pH of the solution at its equivalence point
26
Q

what occurs at the half-equivalence points on titration curves?

A
  • where one-half of the titrant required to reach the equivalence point has been added is also the position where one half of our original acid molecules are deprotonated so they exist in half their original form and half in their conjugate base form
    • at half-equivalence points, pH = pKa
27
Q

equivalence point vs half-equivalence point:

A
  • equivalence point:
    • represents full neutralization
    • moles acid = moles base added
    • solution has virtually no buffering ability
    • located in the middle of a steep part of the titration curve
  • half-equivalence point
    • represents half-neutralization
    • moles acid - moles conjugate base
    • solution acts as a relatively effective buffer
    • located in the middle of a plateau on the titration curve
28
Q
  • all strong acid/strong base titrations have an equivalence point at?
A
  • pH 7
29
Q

the equivalence point for a weak acid/strong base titration is:

A
  • always higher than 7 under standard conditions
30
Q

strong acids/weak base titrations have equivalence points?

A
  • below pH 7 under standard conditions
31
Q

the first proton lost in a polyportic acid most readily corresponds to?

A
  • the largest ka value
    • the second is harder to lose
    • the third one is even harder than the last and has the smallest ka value, so on
32
Q

polyprotic acid titration curves:

A
33
Q

polyprotic titrations of amino acids:

A
  • nonpolar amino acids have only 2 equivalence points
  • acidic and basic amino acids have 3 equivalence points

MCAT chemistry (12 decks)

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