CHY 122 FInal
Which proton is the easiest to remove and why?
- the first!! - as Ka increases, acid strength increases - it is the most willing to donate
What factors affect acid strength?
1) H-A bond polarity 2) H-A bond strength 3) Conjugate base stability
What are the two classes of weak bases?
1) Neutral molecules with a non-bonding pair of electrons 2) anions of weak acids with non-bonding pair of electrons
Two ways to use ICE tables are...
1) When all concentrations are known, find k 2) When initial concentration and k are known, find equilibrium concentration
To calculaye pH using an ICE table
1) Write balanced equation 2) construct ICE table and fill in known values 3) use variables to represent change 4) Use quadration formula OR assume x <<< [ ] initial and ignore x 5) Find x and check assumption 6) Calculate pH
Calculate the pH of a solution when given M and mL
1) calculate moles H+ and moles OH- initial 2) use ICE table to find moles limiting reagent 3) calculate [excess ion] using total volume 4) use pH square to find pH
How to calculate pH of the solution after the addition of mL of compound in a titration
1) calculate moles OH- and moles ----- initial 2) use ICE table to find limiting and excess reagents 3) calculate [excess ions] using total volume 4) calculate pH using HH eqn
What factors influence acidity of carboxylic acids?
1) increased polarity of O-H bond due to presence of second O atom 2) conjugate base exhibits resonance which leads to stabilization of the anion
What are the steps to calculate the concentration of OH- in a solution and the pH of the same solution?
1) write balanced eqn 2) construct ICE table & fill in known values 3) use variables to represent initial [ ] 4) assume change << initial [ ], ignore change in x 5) find variable using kb 6) use stoichiometry
Calculate the # of grams steps
1) write reaction for substance reacting with H2O and kb expression 2) convert pH to [OH-] 3) find [ ] using kb expression 4) use stoichiometry to convert [ ] to get grams of substance
what is Kw equal to at 25ºC?
1.00 x 10^-14
If Ka values differ by at least 1000, only the ____ proton influences pH
1st
Neutralization
A reaction between an acid and a base
Polyprotic
Acids that have more than 1 acidic proton (diprotic, triprotic)
Lewis acids/bases
Broadest, most general definition of acids and bases, the concept of what it means to be an acid can now be expanded beyond H+
How do you tell if acid-base pairs will function as a buffer?
Buffers need a weak base and the conjugative acid
What is a buffers pH range?
Defined as the pH range over which the buffer acts effectively ; buffers typically have a range within +- 1 pH unit of the pKa
Perk of HH eqn
NO ICE TABLE
Conjugate pair is differ by...
One H+
Monoprotic
One acidic proton (H+) ex: (HC2H3O2, HCl, HNO3)
Buffers
Solutions of a weak conjugate acid-base pair the resist drastic changes in pH
Buffer capacity
The amount of acid or base that a buffer can neutralize before the pH changes appreciably
The common-ion effect
The solubility of weak electrolyte will decrease when a soluble compound containing a common ion is added to solution
How do buffers work?
They resist changes in pH
Indicators
Weak acids that differ in color from conjugate base
at the half equivalence point [HA] = ______ and pH = ______
[A-] ; [pKa]
_____ and ____ in the buffer determine the buffer capacity
[HA] ; [A-]
Lewis acid
acts as an electron-pair acceptor
Lewis base
acts as an electron-pair donor
Two examples of buffers...
blood is buffered and so is the ocean!
Within a group...H-A ______ is the most important
bond strength
Henderson-Hasselbach eqn
can calculate the pH of a buffer using this equation if Ka and ration of conjugate acid to base known
As concentration of weak increases, pH _____
changes as well
Binary acids
consist of H and one other element
Oxyacids
consist of H, O, and another nonmetal or metalloid ex: HNO3, HClO4, H2SO4
Titrations are used to...
determine reactant concentrations or the equilibrium constant (k)
end point _______ ______ ______ the equivalence point
does not equal
The place where indicator changes color is the...
endpoint
Weak acid and conjuagte base will be in ______
equilibrium
Relationship between Ka & Kb
for a conjugate acid-base pair: Ka • Kb = Kw
Titration curve
graph of solution pH vs volume of titrant added
an increase in Ka results in acid strength...
increase
As Kb increases, base strength...
increases
H-A bond strength decreases, acid strength...
increases
as electronegativity of 'Y' increases, electron density...
increases
increased stability of A- = acid strength...
increases
polarity increases, acid strength...
increases
Solubility equilibria
ionic compounds are generally strong electrolytes that dissociate when dissolved in water ex: NaCl, BaSO4, CaF2
H-A bond polarity
is there is a positive charge on H and negative of A, the molecule HA will act as an acid
As protons decrease, solutions becomes ____ acidic
less
For a weak acid, the initial pH is ______ than titration of a strong acid
less acidic
indicators should be chosed so the change in color...
occurs near the equivalence point of a titration
Carboxylic acids
organic acids which contain a carboxyl group (-COOH) ex: HCOOH, CH3OOH
Equivalence point
pH at which the moles of acid equals the moles of base
Half equivalence point
pH where 1/2 of the solution has reacted with the titrant
Within a period...H-A _______ is most important
polarity
Strong acid - strong base titration
produces a neutral salt and pH (7.00) at the equivalence point
Weak acid - strong base titration
produces a solution at the equivalence pt with a pH greater than 7
Weak bases
react with water to form a conjugate acid and OH-
Titrant
reactant being added (can be acid or base)
Titrations
reactants are slowly added together while equilibrium concentrations are monitored
increased Ksp = solids ____ dissolve
readily
Characteristics of acid and base will change....
shape of titration curve and pH of equivalence point
When H+ are removed it is a _____ function
step-wise
Conjugate base stability
the more stable the conjugate base A-, the stronger the acid
H-A bond strength
weaker H-A bonds can be broken more easily making HA a stronger acid