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