chapter 14: acid base eqilibrium Flashcards
what are water-soluble ionic compounds
salts
nearly all salts are what
strong electrolytes
what is hydrolysis
when ions are able to react w/ water to generate H+ or OH- ions
how can the pH of an aqueous salt solution can be predicted
qualitatively by considering the ions of which the salt compos
what is an anion, X^-
conjugate base of an acid
what will a strong acid or base do to the pH
they will have no effect on the pH ( and make sure to cancel them out
if you have a weak acid then what is the strength of its conjugate base
the base is also weak
to what extent will acetate ion react with water and what does it do to the pH
react to a small extent
- increases the pH and makes it basic
anions w/ ionizable protons are what
amphoteric
the behavior w/ water is determined by what
the magnitude of Ka or Kb
if Ka > Kb
ion will cause the solution to be acidic
if Kb> Ka
the solution will be basic
polyatomic cations that contain one or more protons can be considered what
conjugate acids of weak bases
what can metal ions react with that will affect the pH
react with water to decrease the pH of an aqueous solution
what other ions do not affect pH
- ions of alkali metals
- heavier alkaline earth metals
what can cause a shift of the electron density in water
attraction between nonbonding electrons on O2 and and the metal
greater charge =
smaller size = more acidic
strong electron interaction characteristics
- greater charge and smaller size
weak electrostatic interactions
- smaller charge = larger size
cation is from a strong base; anion is from a strong acid
pH is neutral
cation is from a strong base; anion is from weak acid
(NaC2H3O2)
basic soln
cation is a conjugate acid of weak base; anion is from strong acid
NH4CL
acidic
what is the formula for a solution
cation + anion
cation is highly charged metal ion; anion is from strong acid
Al(NO3)
acidic
what happens when NaC2H3O2 is added to a solution
- NaC2H3O2 dissociates completely
- increase in C2H3 O2 ions
what does an increase in C2H3O2 ions cause
HC2H3O2—> H+ + C2H3 O2
- equilibrium will shift to the left
- makes more acid
what is the common ion effect
extent of the ionization of a weak electro. is decreased by adding a strong electrolyte that has an ion in common
if you have a concentratoin of a strong acid then what is that concentration also equal to
- H3O + concentration
- use this conc. to calculate pH directly
what is a buffer solution
weak conjug. acid/base pair that resist drastic changes in ph
what can a buffer neutralization not do
consume one another that is why we use weak acids and bases
what pH can you buffer a solution
- at any pH
what are the 3 ways to make an effective buffer
- weak acid and salt contains conjugate weak base
- weak base and salt that contains conjugate weak acid
- two salts that contain different anions that correspond to the same polyprotic acid
NaHCo3 and Na2CO3
HCo3 = was and CO3 is wb
what is the henderson hassbelbalch equation and what is is used for
pH = pKa + log (base/acid)
- calculates pH of a buffer from Ka and initial concs of the weak acid and salt of the conjug base
what happens when a strong acid is added to a buffer
the H+ is consumed by X- to produce HX
what happens when a strong base is added to a buffer
OH is consumed by HX to produce X
what is buffer capacity
the amount of acid to base the buffer can neutralize before the pH begins to change
what does buffer capacity depend on
the amount of acid and base from which the buffer is made
if you have large amounts of conjugate acid-base pair what happens
the more resistant the pH is to change
what is the pH range
range over which the buffer acts effectively
when do buffers most effectively resist change
when the conc. of the weak acid and conjug. base are about the same
- pH = pKa
when ph= pka what does it mean
- optimal pH of any biffer
what is a titration
analytical technique to calculate the conc. of a solute in a solution
what is the standard solution
solution of a known concentration
what is the equivalence point
point at which the two different solutions (known + unknown) are at stoichiometrically equivalent quantitties
what are indicators
dyes that show a color change right past the equivalence point
is the equivalence point found? if not what is found
no, the endpoint is found
what are most indicators
weak acids
what can be used to monitor the progression of a titration curve
a pH meter
what are some characteristics of a strong acid-base titration
- how to measure pH before the addition of the base?
- before base: pH can be calculated from the conc. of the strong acid (-log)
- initial acid conc. starts closer to 1 and is very low and base pH is high
- base is added pH increases and is rapid near the equivalence point
what is the equivalence point and what is the pH
moles of acid = moles of base
- the pH = 7.00
in a strong acid-base titration what happens as more base is added, how do you find the pH
- the pH levels off and pH is determined by the conc. of the excess base
what is the end point
the point where the indicator changes color( approx. the equivalence point)
what are some characteristics of a weak acid-strong base titration
- initial acid starts at a higher pH
- base is at a high pH
in a WA-SB titration how do you determine the pH
the pH is determined by the acid but since it is a weak acid we need to know the Ka
what happens prior to the equivalence point of a WA-SB titration and what happens after
- weak acid is neutralized to the weak base and the solution contains a mixture of the WA and CB
- after we are left with the conjugate of the WA
what happens at the equivalence point of WA-SB
moles acid = moles of base
- base reacts with acid to form a salt
pH >7 because Na+ doesn’t have an effect on pH
what are some titration curve comparisons
- weak acid solns have a higher initial pH than strong acid of the same conc.
- pH change at the rapid rise near the equiv. point is smaller for a weak acid
- pH @ Equiv is >7 for weak acids and 7 for strong acids
why is Ka an important factor in weak acid titrations
- strength of weak acids has an effect on pH curve
- weaker the acid = greater pH value @ equivalence point= shorter vertical region
what are some characteristics of a strong acid-weak base titration
- goes in the other direction
- the initial acid pH is low and base is not that high
- pH @ equivalence is less than 7.00
