Chapter 10 - Acids and Bases Flashcards
what does amphoteric mean?
a substance that can act as both an acid and a base
what is water autoionization?
reacts within itself; One water molecule donates a hydrogen ion to another water molecule to form a hydronium ion and the hydroxide ion; reversible
what is the ionization constant of water?
Kw=[OH-][H+]= 10^-14
what are the concentrations of OH- and H+ in pure water?
always equal; [OH-]=[H+]=10^-14
what is Kw dependent on?
temperature only, not pressure or volume
how does Kw change with temperature?
increases as temp increases
equation for pH?
pH=-log(H+)
equation for pOH?
pOH= -log(OH-)
how are pH and pOH related?
pH + pOH = 14
at what pH is a solution neutral
7
at what pH is a solution acidic?
below 7
at what pH is a solution basic?
above 7
what is a strong acid/base?
completely dissociates in water
what are weak acids and bases?
only partially dissociate in water
what is the acid dissociation constant?
Ka = [H+][A-]/[HA]
what does a small Ka mean?
weaker acid, less dissociation
what is a conjugate acid?
acid formed when base gains a proton
what is a conjugate base?
base formed when acid loses a proton
what is the conjugate of a strong acid or base?
a very weak acid/base
what is the (typical) conjugate of a weak acid or base?
a weak acid or base
what is a neutralization reaction?
when acids and bases react with each other to form a salt and often water
pH of reaction between equimolar amounts of strong acid and base?
7
pH of reaction between strong acid and weak base?
below 7
pH of reaction between weak acid and strong base?
above 7
pH of reaction between weak acid and weak base?
depends on relative strength of the reactants
what is titration used for?
to determine the unknown concentration of a known reactant in a solution
how is a titration performed?
performed by adding small volumes of known concentration (the titrant) to a known volume of a solution of unknown concentration (the titrand) until completion of the reaction is achieved at the equivalence point
when is the equivalence point reached in acid base titrations?
equivalence point is reached when the number of acid equivalents present in the original solution equals the number of base equivalents added or vice versa
does the equivalence point always occur at pH 7?
NO!!!
what happens when you titrate a polyprotic acid or base?
there are multiple equivalence points – each conjugate species is titrated separately
what are the two methods for determining equivalence point>
evaluating by graphical method, plotting the pH of the unknown solution as a function of added titrant , or estimated by watching for a color change of an added
what are indicators?
weak organic acids or bases that have different colors in their protonated and deprotonated states
what makes a good indicator?
Must be a weaker acid or base than the acid or base being titrated or else it will be titrated first, To choose an ideal indicator, select the indicator that has the closest pKa to the pH of the equivalence point
at what point does the indicator change color?
the endpoint, if the indicator is chosen well then the volume difference is negligible
how can you estimate the equivalence point on a titration graph?
locating the midpoint of the region of the curve with the steepest slope
equivalence point for strong acid and strong base titration?
pH=7
equivalence point for weak acid with strong base?
pH>7
equivalence point for weak base with strong acid?
pH<7
equivalence point for weak acid with weak base?
near neutral
describe a polyprotic species titration curve
o flat part of curves are buffer regions
o center of the buffer region sometimes called the half-equivalence point because it occurs when half of a given species has been protonated (or deprotonated)
o equivalence point occurs when all of the species is titrated (rapid change in pH occurs at this point)
o second buffer region and second half-equivalence point at the flat part of the graph
what equation can you use to solve for titrations?
MV=MV
what is a buffer solution composed of?
mixture of a weak acid and its salt (conjugate base plus cation) or a mixture of a weak base and its salt
what does a buffer solution do?
resist changes in pH when small amounts of acid or base are added
what is the bicarbonate buffer system?
H2CO3/HCO3- conjugate pair in the plasma component of the blood, weak acid buffer for maintaining the pH of blood
equation for bicarbonate buffer system
CO2+H2O⇌H2CO3⇌H^++HCO3-
what is the henderson hasselbach equation?
pH=pKa + log [A-]/[HA]
when does pH=pKa
when [A-]=[HA], occurs at half-equivalence point, buffering capacity at optimal
what happens when you change the concentrations of A- and HA but keep the same ratio?
will not change the pH but will change the buffering capacity
