CHEM 112 - MIDTERM III Flashcards
When titrating a weak acid (HA) with a strong base (OH-) what is left in the solution & equivalence point?
- left in the solution: H2O + A- (weak conjugate base)
-equivalence point: moles OH- added = moles HA in original solution
When titrating a weak base (A-) with a strong acid (H+) what is left in the solution & equivalence point?
-left in the solution: H20 + HA (strong conjugate acid)
-equivalence point: moles H+ added = moles A- in original solution
When we add a strong acid to the buffer, what happens?
Neutralization reaction occurs; acid is neutralized, consuming the conjugate base and producing conjugate acid –> [A-] decreases and [HA] increases
When we add a strong base to the buffer, what happens?
[A-] increases and [HA] decreases
- Divide moles by total volume of solutions to find new concentrations of [HA] and [A-] AFTER neutralization is complete
- Plug in equilibrium equations in Henderson-Hasselbalch equation to find pH
Calculation of pH in the buffer region
- Write out dissociation rxn (find out which reagent is being consumed, in a weak acid (first) and strong base, the base will be consumed)
- Calculate the moles of HA (initial HA)
- Calculate moles of OH- (initial OH-)
- Use modified ICE table (using moles and subtract OH- from initial weak acid moles)
- Use total volume of solutions to find new concentrations of the weak acid and conjugate base
- Use H-H equation
Calculation of pH at the equivalence point
- Determine # of moles of OH- to get to the equivalence point
- Determine the volume of OH- needed to get the moles calculated in (1)
- Determine the new total volume
- Determine the new concentration of the conjugate base (A-)
- Complete a pH calculation for a weak base with the initial concentration determined in (4)
Calculation of pH beyond equivalence point
- Beyond the equivalence point, OH- is in excess. Calculate [OH-] by subtracting the initial number of moles of H3O+ from the number of moles of added OH- and by dividing by the current total volume
- Calculate pOH and use this to find pH
Between the initial pH and equivalence point, the solution becomes a _____.
buffer
Halfway to the equivalence point the pH = ____
pKa
In the buffer region, we use the stoichiometry and the _____ equation to calculate the pH
Henderson-Hachelbach
At the equivalence point, the acid has been converted to conjugate base. We calculate pH by _____
Working an equilibrium problem for the ionization of water by the ion acting as a weak base
Beyond the equivalence point, OH- is in excess, we calculate the pH by ____
Calculating [OH-] by calculating moles of OH- and subtracting from the acid (HA) and dividing the moles by the total volume. Find pOH and subtract from 14 for pH
Salts are ____
ionic compounds dissolved in water to form aqueous solutions
The extent of a dissociation describes the _____ of the ionic compound
solubility
If an ion does NOT have a Ksp value, what does that mean?
They are fully soluble in solutions
Salts that contain _____ are almost always soluble
Na+, K+, Cl-, and NO3-
Most other salts are ____ to some degree
insoluble
Ksp
Solubility product constant; measures how soluble a compound is
If Ksp is very small then ____
the ion concentrations are very small and the compound is not very soluble
Solubility products are usually highlighted by ____ arrows
double
Molar solubility
the number of moles of solute per 1 L of a saturated solution (mol/L)
Solubility
the number of grams of solute in 1 L of a saturated solution
When Q is ____ than K, a precipitate will form
>
If there are two possible precipitates that can form, the one with the ____ Ksp will precipitate first
smallest
If the concentrations of ions in solution of a slightly soluble salt (one with a Ksp) exceed the value of the ____ of that salt, a precipitate will form
molar solubility
Entropy (S)
The level of disorder in the system (ie. disordered bedroom - positive entropy because it takes energy to put your room back in order)
Entropy increases if the state of matter changes in the following directions:
Favoring free particle movement!!
solid -> liquid
solid -> gas
liquid -> gas
Entropy also increases if the _____
number of gas particles increases (or level of disorder for particles increases)
Entropy increases if the ____ of a reaction increases
temperature
Entropy increases specifically with a _____ reaction
exothermic (releasing energy to surroundings)
Entropy decreases with a _____ reaction
endothermic (heat is taken from surroundings)
Enthalpy (Delta H)
Describes how much heat is exchanged with the surroundings
A spontaneous process is one that _____
occurs without outside intervention
Entropy of the universe
Entropy of the rxn + Entropy of the surroundings
Entropy of a rxn can be spontaneous if the ____ increases to a great extent
Delta S of the surroundings (ie. freezing water)
Gibbs Free Energy (Delta G)
Describes total energy change for the system
G < 0
spontaneous
G > 0
non-spontaneous
Delta G will move in the direction that is _____ to reach equilibrium
spontaneous (ie. the negative forward rxn vs. the positive reverse, etc.)
If the rxn is ALWAYS spontaneous, we can assume that entropy and enthalpy are ____
both negative!
If the rxn is ALWAYS non-spontaneous, we can assume that entropy and enthalpy are ___
both positive!
If the temperature of the surroundings increase, the rxn must be ____
exothermic
If the temperature of the surroundings decrease and absorb heat, the rxn must be _____.
endothermic
Changing from liquid to gas will result in a ____ enthalpy
positive (endothermic) bc it takes energy to vaporize
G Naut indicates the ____
Gibbs free energy change under STANDARD conditions (ie. 25 degrees Celsius)
Oxidation
When an atom/element LOSES electrons (LEO)
Reduction
When an atom/element GAINS electrons (GER)
Oxidizing agent
Oxidizes another substance (and itself is reduced)
Reducing agent
Reduces another substance (and itself is oxidized)
Procedure for Balancing Redox Reactions
- Determine what is being oxidized and reduced
- Write separate half reactions to balance
- Balance atoms by adding H2O to balance O, balance H by adding H+ and balance the charge of each half reaction by adding electrons
- Make the number of electrons in each half reaction the same to cancel them out of the entire reaction
- Add the two half reactions together
- (IF BASIC): add OH- to each side to neutralize H+
In a Galvanic Cell, electrons are produced at the _____
anode
Oxidation occurs at the _______ in a galvanic cell
anode
In a Galvanic Cell, electrons are accepted at the _____
cathode
Reduction occurs at the ____ in a galvanic cell
cathode
Salt Bridge
allows bystander cations and anions to move from one compartment to the other
Electrodes
the solid metal bars connected by the conductive wire of a battery (allows electrons to flow)
In the galvanic cell, electrons flow from the _____ to the ____
anode to cathode (ACE)
Cell diagram convention w/ single and double lines
(anode solid) l (anode ion) ll (cathode ion) ll (cathode solid)
where the double line represents the salt-bridge separating the two half reactions
Standard cell potential (emf)
Ecell = E (cathode) - E (anode) ; the difference of the standard reduction potentials of the cathode and the anode
Standard reduction potentials are _____ prooperties
intensive properties; independent of the stoichiometry applied with balancing the redox reaction
The more positive Ecell value is the _____, which includes the ____ reaction
cathode (pawwwsitive); reduction
The reduction reactions have the electrons on the ____ side of the reaction
reactant
Diagonal Rule Of Ecell Half Reactions
A species on the left of a given half-cell reaction will oxidize the product of the second reaction
The more positive the Ecell potential, will oxidize the other rxn’s solid and will reduce itself
Ecell > 0, the redox reaction is _____
spontaneous (G < 0)
Ecell < 0, the redox reaction is _____
nonspontaneous (G > 0)
