Chm 142 exam 3

common ion effect

The common ion effect is a phenomenon in which the addition of a common ion to a solution shifts the equilibrium of a chemical reaction involving that ion. This effect is commonly observed in acid-base and solubility equilibria. The presence of a common ion reduces the solubility of a slightly soluble salt, and decreases the ionization of a weak acid or base.

If a solution contains a weak acid/base and its conjugate base/acid pair ion then….

the weak acid/base won’t dissociate as much as if it were alone in the solution

Buffer

solutions of a weak conjugate acid-base pair that **resist** drastic changes in pH are called buffers

a good buffer contains relatively ___ concentrations of **both** the acid and base. Their concentrations are ______________

high

approximately equal

How to make a buffer

1. mix a weak acid and a salt of its conjugate base
2. mix a weak base and a salt of its conjugate acid
3. add a strong acid and partially neutralize with a weak base
4. add a strong base and partially neutralize with a weak acid

Henderson-Hasselbalch equation

only applies to **buffers**

\[A-\] is the concentration of the conjugate base

\[HA\] is the concentration of the acid

Buffer capacity

the amount of acid or base the buffer can neutralize before the pH begins to change to an appreciable degree

pH range of a buffer

range: pKa +/- 1 pH unit

The addition of a strong acid or base to a buffer is __________

neutralization reaction

First, calculate new values of \[HA\] and \[A-\] using naMbVb = nbMaVa or using an ICE table. Then, use the Henderson-Hasselbalch equation to find pH

Titration

an acid (or base) solution of **known concentration** is slowly added to a base (or acid) solution of **unknown concentration**

Equivalence point

when stoichiometrically equivalent quantities of acid and base have been brought together in a titration

For the titration of a **strong acid** with a **strong base**, at the equivalence point the pH will be _____

pH = 7.0

For the titration of a **weak acid** with a **strong base**, the pH will be determined by ______

Initial pH: will use Ka for the weak acid

**pH after initial but before equivalence point**: First, calculate the moles of weak acid, the moles of base added. Then, subtract moles of base from moles of acid. Finally, use the Henderson-Hasselbalch equation.

pH at equivalence point: use Kb for the conjugate base of the weak acid

For the titration of a **weak acid** with a **strong base**, the equivalence point will be reached at _______

pH > 7

When a polyprotic acid is titrated, there is an _____________ for each dissociation

equivalence

diprotic have two, triprotic have three

pH = pKa when ……..

you have reached halfway to the equivalence point

solubility product constant

\-Ksp

\-can be used when a strong electrolyte is dissociated

\-is NOT the same as solubility

\-is unitless

if one of the ions in a solution equilibrium is already dissolved in the solution, the solubility of the salt will _________

decrease

If a substance has a **basic ion**, it will be more soluble in _______ solution

acidic

the formation of complex ions ________ the solubility of the salt

increases

complex ion

an assembly of a metal ion and a lewis base

lewis acid

electron acceptor

lewis base

electron donor

amphoteric

can act as either an acid or a base

Q = Ksp

the system is at equilibrium and the solution is saturated

Q < Ksp

the solution is unsaturated and more solid can dissolve

Q > Ksp

the solution is supersaturated and a precipitate will form

Enthalpy (H)

is the heat absorbed by a system during a constant pressure process

is a state function

Entropy (S)

is a measure of the randomness in a system

is a state function

Gibbs Free Energy (G)

depends on both H and S. The sign reveals if a process is spontaneous.

is a state function

spontaneous process

a process that proceeds without any outside assistance

can be either slow or fast

processes that are spontaneous in one direction are nonspontaneous in the reverse direction

Reversible process

we can restore the system to its original condition with no change to the surroundings

Hypothetical, there are no real processes that are reversible

Irreversible process

the surroundings are somehow changed when the system is restored to its original state

Isothermal process

a process that occurs at a constant temperature

the entropy (S) of the **universe** _________ in any spontaneous process

increases

Standard enthalpy of formation (ΔH\*)

are measured under standard conditions

298 K and 1 atm

Microstate

a single possible arrangement of the positions and kinetic energies of the molecules when the molecules are in a specific thermodynamic state

Boltzmann’s equation

S = k ln(w)

where W represents the number of microstates

S is entropy

k is Boltzmann’s constant

things that result in increased entropy

\-increased volume

\-increased temperature

\-increased number of molecules

\-more atoms in a molecule

\-entropy of gases > entropy of liquids > entropy of solids

Third law of thermodynamics

the entropy of a pure crystalline substance at absolute zero is 0

For a spontaneous process, ΔG is ____

negative

For a system at equilibrium, ΔG is _______

0

For nonspontaneous reaction in the forward direction (but spontaneous in the reverse), ΔG is ______

positive