Chem #10 Flashcards
what makes a stronger base
a stronger base has more EDG that would be able to stabilize a positive charge when a hydrogen is added
what does the Arrhenius definition of acids and bases refer to?
dissociation to form H+ or OH- ions
o Typically limited to aqueous acids and bases
o Very restrictive
Arrhenius acid
will dissociate to form an excess of H+ in solution
Have H at the beginning of their chemical name.
Arrhenius base
will dissociate to form an excess of OH- in solution
Have OH at the end of their chemical name.
what does the Bronsted-Lowry definition of acids and bases refer to?
donating or accepting H+
Bronsted-Lowry Acid
a species that donates H+
Bronsted-Lowry base
: a species that accepts H+
conjugate acid/base pairs
transfer of a proton from acid to base.
what does the Lewis definition of acids and bases refer to?
donating or accepting an electron pair
o Also known as coordinate covalent bond formation, complex ion formation, or nucleophile-electrophile interactions.
lewis acid
an electron pair acceptor
lewis base
electron pair donator
amphoteric species
one that reacs like an acid in a basic environment and like a base in an acidic environment.
o Amphiprotic: can gain or lose a proton.
o Ex: H2O and HSO4-
o Also species that can accept or donate electrons.
autoionization of water
water can react with itself.
For pure water at 298 K, the water dissociation constant Kw = 10-14
• Kw is only affected by temperature, not concentration, pressure, or volume changes.
lower pH is ___
acidic
higher pH is ___
basic
strong acids and bases
completely dissociate into their component ions in aqueous solutions.
o Contribution of ionization of water is only important if the concentration of the strong acid or base is near 10-7.
weak acids and bases
only partially dissociate in aqueous solutions, and the less it will dissociate.
acid dissociation constant
Acid dissociation constant, Ka
• The smaller the Ka, the weaker the acid.
base dissociation constant
Base dissociation constant, Kb
• The smaller the Kb, the weaker the base, and the less it will dissociate.
conjugate acid
the acid formed when a base gains a proton
conjugate base
the base formed when an acid loses a proton.
a strong acid has a ____ conjugate base
weak
EWG near an H on an acid _____ its acidic capabailities
increase
polyvalent
each mole of the acid or base liberates more than one acid or base equivalent.
2 M of H3PO4 has a normality of ____
6
titration
a procedure to determine the concentration of a known reactant in solution.
o Titrations are performed by adding small volumes of a solution of known concentration (titrant) to a known volume of a solution of unknown concentration (titrand) until completion of the reaction is achieved at the equivalence point.
titrant
gets added
titrand
added to (usually trying to find out its concentration)
indicator
weak organic acids or bases that have different colors in their protonated or deprotonated states.
o Used in low concentrations to not alter the equivalence point.
o Endpoint: the point at which the indicator changes to its final color.
o If the indicator is picked well and the titration is done right, the volume difference between the endpoint and the equivalence point is negligible.
endpoint
o Endpoint: the point at which the indicator changes to its final color.
how should the indicator be selected?
Select the indicator that has the closest pKa value to the equivalence point.
Should be chosen closest to the endpoint
describe the titration: strong acid with strong base
o Equivalence point is 7
o The acid dominates at low addition of strong base and the base dominates after the endpoint.
o Drastic change in the middle.
o Equivalence point using a pH meter is the midpoint region of the curve with the steepest slope.
describe the titration: weak acid with strong base
o Equivalence point >7
o The initial pH is greater than for the strong acid starting solution ^^
o The pH changes gradually early on and has a less sudden rise at the equivalence point.
describe the titration: strong acid with weak base
o Equivalence point <7
o Initial pH is in the basic range.
o Gradual decrease in pH and once again not as steep of a slope as in the strong-strong condition.
describe the titration: weak acid with weak base
o Equivalence point near pH 7
o Very gradual equivalence point
titration curve for polyvalent acids and bases
o Have two buffer regions, half equivalence points and equivalence points
o Acidic or basic amino acids have 3 equivalence points
half equivalence point
when half of the given species has been protonated or deprotonated.
when the acid = conjugate base and vice versa
half equivalence point
when half of the given species has been protonated or deprotonated.
when the acid = conjugate base and vice versa
buffer solution
consists of a mixture of a weak acid and its salt or a weak base and its salt.
o Resist changes in pH when small amounts of acid or base are added.
o The Bicarbonate Buffer system
H2CO3/HCO3- conjugate pair in the blood
Acidosis, breath heavier, blow out more CO2, shift left and reduce H+ in blood.
henderson hasselbach equation
used to estimate the pH or pOH of a buffer solution.
o [HA] = [A-], pH = pKa, buffer is at its best
o Buffering capacity: the ability to which the system can resist changes in pH
Doubles if concentrations are double for the conjugate pairs.
every arhenius acid or base is a ______ acid and base
bronsted lowry (but not other way around)
every bronsted lowry acid or base is a ____ acid or base
lewis
amphoteric vs. amphiprotic
amphoteric: acts like an acid or base depending on the environment
amphiprotic: can gain or give away a proton
zwitterions have both ______ character
anionic and cationic
HClO
hypochlorous acid
HClO2
chlorous acid
HClO3
chloric acid
HClO4
perchloric acid
HNO2
nitrous acid
HNO3
nitric acid
H3BO3
Boric acid
H2CrO4
chromic acid
a ____ is never isolated in solution as it is always attached to water or some other species that has the ability to accept it
H+
the value of Kw changes at different _____
temperatures
Changing pressure, volume, and concentration will not change the Kw.
is the autoionization reaction endothermic or exothermic?
endothermic
what is a p scale?
a p scale is defined as the negtive logarithm of the number of items.
pH + pOH = 14 only holds at _____
298 K (because that is when the kw = 10^-14)
a pH of 1 is ____ while a pH of 10 is ____
acidic
basic
if the concentration of an acid or base is close to 10^-7, then the contribution from ______ is important to consider
the autoionization of water
if they are greater than 10^-7, then don’t worry about it.
what are the strong acids?
HCl, HBr, HI, H2SO4, HNO3, HClO4
does the pH scale go past 0 and 14?
yes, at very strong or very basic solutions.
a strong acid _____ dissociates to produce a ____ solution
completely
concentrated (as opposed to dilute)
a Ka or Kb value less than ____ is considered for a weak acid or base
1
Kw = what?
multiplying the Ka and Kb for an acid and conjugate base or base and conjugate acid
MUST BE CONJUGATE ACID/BASE PAIRS
a strong acid will produce a ____ conjugate base
weak (based on Ka x Kb = Kw)
acids that have ______ elements nearer to acidic hydrogens are stronger than those that do not
electronegative
explain the assumptions when doing problems that deal with Ka or Kb
the assumption is that the value of x (how much acid or base is dissociating) is less than 5% of the original concentration of acid or base. This is oftentimes true when the Ka is 100 times less than the concentration of the starting solution.
the pH of a reaction between a strong base and weak acid is ____ and the pH of a reaction between a strong acid and a weak base is
basic (above 7)
acidic (below 7)
What is the normality of a 2M solution of H3PO4
6 N
Typically, we know the concentration of the ____ but not the ____ in a titration
titrant
titrand
what are the units for normality?
equivalence per volume
______ are weak organic acids or bases that have different colors in their protonated and deprotonated states.
indicators.
the indicator must always be _____ than the acid or base being titrated
a weaker acid or base
the point at which the indicator changes to its final color is not the equivalence point but rather the ____
endpoint
the indicator has a ___ value very close to the _____ of the equivalence point
pKa
pH
If I am titrating HCl with NaOH, which is the titrant and which is the titrand
titrant is NaOH and titrand is HCl
What are 3 differences between the titration curve for strong acids/strong bases and weak acids/strong bases
- the initial pH of the acidic solution is higher because it is a weak acid
- the slope of the curve is greater at first and the slope at the equivalence point is not as steep
- the equivalence point is greater than 7 (due to the presence of the strong base with a weak acid).
amino acids with acidic or basic side chains have _____ equivalence points
3
____ solutions have the useful property of resisting changes in pH when small amounts of acid or base are added
buffer
buffers work by ____
shifting the reaction to form either more of the weak acid or weak base which does not have an effect on the pH.
what is the range of optimal activity for buffers?
+/- 1 the pKa
what equation is used to estimate the pH or the pKa of a buffer solution?
the henderson hasselbach equation
a weak acid and weak base titration combo will have an equivalence point where?
depends on the relative strengths of the acid and base
If given the concentration of H2SO4, the concentration of H3O+ is ____ this concentration
double, because it has 2 H+ ions to donate
