Module 4 Flashcards
Units of Molarity (M)
moles per liter
Units of Molality (m)
moles of solute per kg of solvent
Units of Mole Fraction (X)
Moles of solute / total moles in solution
Units of solubility
grams / liter
When is the delta H of solution greater than zero?
During cooling
When is the delta H of solution less than zero?
During heating
Calculate mass ratio
mass of solute / mass of solution
No units
Henry’s Law: the concentration of a gas dissolved into a liquid is proportional to the pressure of the gas in question
C = (k)(P)
C’s units are M, molarity
k is a constant, different for each system. units are M/atm or mol/Latm
P’s units are atm
What do colligative properties depend on?
The amount of solute in a solution
NOT the identity of the solute!
How is concentration most often given?
As % (w/v), implied units are g/mL
Molecules inside brackets, for example [O2], denotes the concentration of the substance
What states of matter should you NOT use when calculating Keq?
Liquid and solid.
Keq is really only designed for aqueous and gaseous states
When Keq > 1 …
…products are favored more than the reactants
When Keq < 1 …
…reactants are favored more than the products
How do partial pressures behave in ideal solutions?
In ideal solutions the partial pressure of each compound is proportional to its mole fraction
Pi = (xi)(Pi0)
Increasing solubility will allow…
…more of the solute to dissove
Decrease solubility will allow…
….less of the solute to dissolve, or if the solution is already saturated some of the solute will fall out of the solution and form a precipitate
In a liquid solvent, a decrease in temp of a gaseous solute…
Increases solubility
In a liquid solvent, an increase in temp of a gaseous solute…
Decreases solubility
In a liquid solvent, a decrease in pressure of a gaseous solute…
Decreases solubility
In a liquid solvent, an increase in pressure of a gaseous solute…
Increases solubility
In a liquid solvent, an increase in temp of a liquid or solid solute…
Increases solubility
In a liquid solvent, a decrease in temp of a liquid or solid solute…
Decreases solubility
In a liquid solvent, an increase in pressure of a liquid or solid solute…
Has no effect on solubility
In a liquid solvent, a decrease in pressure of a liquid or solid solute…
Has no effect on solubility
How does osmotic pressure, temperature, and volume relate to solubility?
Π = (n/V)RT = MRT
Π is osmotic pressure
n = moles
V = volume in liters
R = gas constant, Latm/molK
T = temp in Kelvin
M = concentration in mol/L
How does the reaction quotient Q differ from Keq?
Q tells us the concentrations of reactants and productsunder any circumstances.
Keq reflects concentrations of reactants and products only at equilibrium
What will happen to the system when Q > Keq?
The system will reverse and favor the reactants
What will happen to the system when Q < Keq?
The system will go forwards and favor the products
How do systems in equilibrium respond to stress? (also what defines stress?)
The system will try to remove or lower the effect of the stress by favoring the reactants or products more.
Stress includes changes in concentrations, volumes, temps, and pressure, etc
What units should you use for the stuff in brackets when calculating Kc?
mol/L
What units should you use for the stuff in brackets when calculating Kp?
atm
Never divide by volume with Kp, just use the atm!
Calculate percent ionization
(M ion / M acid) x100
concentration of ion /
concentration of acid
Why can water behave as both an acid and a base?
Water is amphoteric, it can both accept and donate protons
It is autoionizing. It can interact with itself to ionize
ex: H2O + H2O <–> H3O+ + OH-
Definition of a conjugate acid/base pair
Two molecules that are related by the loss of a proton (H+)
Mathematically, how is conjugate acid/base strength related?
Inversely.
A strong acid’s conjugate base is so weak that it’s a non base (et vice versa)
The stronger the acid, the weaker the conjugate base
Definition of acid dissociation
When an acid dissociates and transfers a H+ onto water, turning itself into its conjugate base.
Note that the breaking apart of the acid and the addition of the H+ to water is simultaneous. The H+ is never free floating.
Acid dissociation is an example of a proton-transfer reaction
Properties of strong acids
Completely dissociates in H2O
No strong acid left at equilibrium
Conjugate bases are non-bases
HCl, HBr, HI, HClO, HNO3, H2SO4
What does it mean when we say that water is leveling?
It means that there cannot be an acid stronger than the conjugate acid of the solvent.
In the presence of an acid stronger than hydronium, water will behave as an acid and turn into hydronium cations
In the presence of a base stronger than hydroxide, water will behave as a base and turn into hydroxide anions
What is the definition of a strong acid or a strong base?
Acid: being stronger than hydronium
Base: being stronger than hydroxide
Properties of weak acids
Only partially dissociates in water, creating an equilibrium
The conjugate base of a weak acid is another weak base
Exists between the strengths of H3O+ and OH-
All four species (weak acid, conjugate weak base, water, water’s conjugate) are present at equilibrium
What is Ka?
The designated equilibrium constant for a weak acid
What is Kb?
The designated equilibrium constant for a weak base
When will the addition of salts to a solution change the solution’s pH?
When the components that the salt dissolves into have conjugate weak acids and bases
Will this change the pH of a solution?
NaBr –> Na+ + Br-
No.
Conjugate acid of Br- is HBr, a strong acid. Strong acid’s won’t affect the pH here.
Conjugate base of Na+ is Na(OH)2, a strong base. Won’t affect pH
Will this change the pH of a solution?
NaOBr –> Na+ + OBr-
Yes.
OBr-‘s conjugate acid is HOBr, a weak acid. Weak acids change the pH here
