CHapter 7 flashcards
QA
what Solvent is widely used?
Water
Electrolyte
form ions when dissolved in water and produce solutions that conduct electricity
A Bronsted acid
is a proton donor (H+ ion)
Bronsted acid
proton is an acceptor (H+ ion)
What happens when an HCl molecule dissolves in water?
A hydrogen bond forms between the H atm of HCl and the O atom of a neighboring H20 molecule, and the nucleus of the hydrogen atom (H+) is pulled out of the HCl molecule
When an oxide ion is added to water?
it exerts such a strong attraction on the nucleus of a hydrogen atom in the neighboring water molecule that that nucleus is pulled out of the molecule. As a result, the oxide ion and water form two hydroxide ions
Conjugate Base
is the species formed when an acid loses a proton. EX: acetate ion is the conjugate base of acetic acid
Conjugate acid
species formed when a base accepts a proton. EX: ammonium ion is the conjugate acid of ammonia
Amphiprotic solvents
solvent that can act either as an acid or as a base, e.g. water, methanol
Autoprotolysis
self-ionization
As a result of autoprotolysis, pure water consists of hydronium ions and hydroxide ions as well as water molecules. The concentration of ions that results from autoprotolysis is only about 10^-7 mol/L, so only about 1 molecule in 200 million is ionized.
Differentiating Solvent
various acids dissociate to different degrees and thus have different strengths
leveling solvent
several acids are completely dissociated and are thus of the same strength
equilibrium reaction
reactions never result in complete conversion of reactants to products. Instead they proceed to a state of chemical equilibrium in which the ratio of concentrations of reactants and products is constant
Equilibrium Constant Expressions
wW+xX->yY+zZ
K=([Y]^y[Z]^z)/([W]^w[X]^x)
The square bracketed terms have the following meaning: 1. Molar concentration if the species is a dissolved solute
2. partial pressure in the atmosphere if the species is a gas
3. If one (or more)species is a pure liquid, a pure solid, or the solvent present in excess, no terms for this species appear in the equilibrium constant expression
Le Chatelier Principle
States that the position of an equilibrium always shifts in such a direction as to relieve a stress ( caused by changing concentration, temp, pressure, etc.,) that is applied to the system
Mass action affect
is a shift in the position of an equilibrium caused by changing the concentration of one of the reactants or products in a system
Common ion effect
If the concentration of one of the ions in solution is increased then the concentration of the other is decreased to maintain a constant value of Ksp
Solubility Product Constants
for sparingly soluble salts
P functions
of a numerical datum is the negative logarithm to the base 10 of that datum
pX =-log X
Weak acid constants
incomplete dissociation
Ka=(h30+)(NO2)/(HNO2)
weak base constants
Incomplete dissociation
Kb=(NH4+)(OH-)/(NH3)
Kw=KaKb
KB=(NH4+)(H3O+)/(NH4+)
Ka=(NH3)(H3o+)/NH4+
KaKb=(OH-)(H3o+)=Kw
dissociation constants for conjugate acid/base pairs
Kw=KaKb
pKw=14=pKa+pKb
buffer solutions
buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid that resists changes in pH of a solution
Buffer action
depends on the donation of protons by the weak acid molecules, HA, when a strong base is added and the acceptance of protons by the conjugate base ions, A-, when a strong acid is added.
A buffer solution contains a?
Sink for protons (a
weak base) that are supplied when a strong
acid is added and a source of protons (a weak
acid) to supply to a strong base that is added.
The joint action of the source and the sink
keeps the pH constant when a small amount of
either strong acid or strong base is added
Properties of buffer solutions- effect of dilution
pH of buffer remains independent of dilution until the concentrations of the species it contains are decreased to the point where the approximations become invalid
Buffer capacity
of a buffer is the number of moles of strong acids or strong bases that 1L of the buffer can absorb without changing pH by more than 1. When conjugate acid and base are present at similar
concentrations, the pH changes very little as more strong
base (or strong acid) is added.
