CHM 142 Exam 3 Flashcards
How does bond polarity affect acidity?
The more polar the bond the stronger the acid
How does bond strength affect acidity?
The stronger the bond the weaker the acid
How does the stability of an acids conjugate base affect acidity?
The more stable the conjugate base is the stronger the acid is
Down a group acidity —-
increases bc/ bonds are weaker
Across a period acidity —
increases bc/ polarity increases across the periodic table
acids made of H + O and one other electronegative atom
Oxyacids
How does the addition of more electronegative atoms (like O) affect oxyacid acidity?
The more electronegative atoms bonded to the central atom the more acidic it is
the more O the more acidic it is
-ate changes to
-ic + acid
-ite changes to
-ous + acid
acids that contain a carboxy group
carboxylic acids
Carboxyl group
COOH
electron pair acceptor
gets more negative
Lewis acid
electron pair donor
gets more positive
Lewis base
All bronsted lowry acids and bases are also —
Lewis acids and bases
When a weak electrolyte and a strong electrolyte (with a common ion) are in a solution together causes the weak electrolyte to ionize/ dissociate less than it normally would if it were alone
Common ion effect
Does the common ion effect change Keq?
No it does not
If more base is added to a buffer what is its effect?
More A- is produced
OH- + H+—H2O+A-
If more acid is added to a buffer what is its effect?
More HA is produced
H+ + A- —HA
solutions that contain high concentrations (10^3<) of acid-base pairs that are resistant to pH change
Buffer solutions
Why are buffer solutions resistant to pH change?
Bc they contain both a weak acid and a weak base to neutralize strong acids or bases
What are the two ways to make a buffer?
- Mix a weak acid (or base) with a salt of that acid (or base)
- Make the conjugate acid base pair from mixing a weak base (or acid) with a weak base (or acid)
Henderson Hasselbalch equation
pH=pKa +log([base]/[acid])
the amt of acid/ base that can be added to a buffer before the pH changes significantly
Buffer capacity
when choosing a buffer you chose one that has a — that is close to the desired —
pKa, pH
Titration
an acid or base of unknown concetration is added to a solution of known concentration
pH change is monitored by indicator or by pH probe
Can a titration be done with two weak reactants?
aka add weak base or acid to a diff. weak base or acid
No because that would result in multiple eq points
What should you consider when choosing an indicator for a titration?
The indicator should change color in the general pH that the eq point occurs otherwise the color change provides no useful information
equivalence point
the point where there are stoichiometrically equivalent amounts of acid and base in a solution
the point where and indicator changes color, approximates/slightly overestimates the equivalence point
End poimt
Does not = the equivalence point
a graphical representation of a titration that shows the starting pH, ending pH and equivalence point
Titration curve
explain the main points of a strong acid-strong base titration curve
- s- shaped curve
- pH is at 7
if its a strong base-strong acid - high starting pH and low ending pH
Explain the main points of a weak acid-strong base titration curve
- similar to a strong-strong curve
- rapid rise is shorter than a strong-strong curve
- eq points occurs >7 pH in an weak acid-strong base
- eq point occurs <7 pH in a weak base strong acid
Explain the main points of polyprotic acid curve
- more snake shaped than s shaped bc there is more than one eq point (bc >1 H to remove)
- You can find pka from the halfway point between the eq. points
indicates how soluble a solid is in a aqueous solution
Solubility product constant (Ksp)
what are three factors that affect solublility in ionic compounds?
- Presence of common ions
- pH of the solution
- formation of complex ions
how does the common ion effect have effects on solubility?
the presence of a common ion will decrease the solublity of a compound
aka will dissociate less than it normally would
how does the pH of a solution affect solubility?
For compounds with basic anions the solubility is increased in strong acidic solutions
solubility increases with increasing [H+]
how does the formation of complex ions affect metal ion solubility
complex ions have high Keqs which means they have high solubilitys
aka solubiliity increases with the formation
metal ion + lewis bases
complex ions
what are some ions that are amphoteric?
Al3+, Cr3+, Zn2+,Sn2+
metal oxides/ hydroxides that don’t dissolve in water but will dissolve in very basic or acidic solutions
amphoteric oxides/hydroxides
why do amphoteric hydroxides/ metal oxides dissolve in acidic solutions
their basic anions interact with the H+ in acids
why do amphoteric hydroxides/ metal oxides dissolve in basic solutions
they form complex ions in basic solutions
what does Q =Ksp tell you about a solution
the solution is saturated
what does Q>Ksp tell you about a solution
the solution is super saturated and a precipate will form
what does Q<Ksp tell you about a solution?
the solution is unsaturated and no precipate will form
processes that proceed with no outside assistance
Spontaneous Process
all — processes are real processes
spontaneous
True or False? spontaneous processes can be fast or slow
True
Spontaneous processes proceed in — direction
One
aka non spontaneous in the other direction
Non-spontaneous processes do not equal —
impossible
they only require outside assistance
Examples of state functions
E, H, S G, T
what two factors are not state functions?
work and heat
Reversible processes
Processes that do not experience any change when they are returned to their original state
hypothetical processes
Irreversible Processes
Systems will experience a change when returned to their original state
real processes
The change in heat of a system during constant P.
Enthalpy (H)
state function
the randomness of a system OR the tendency of a particles to disperse and decrease their ability to do work
Entropy (S)
state function
Equation to find the change in Entropy (S)
= qrev/ T
T in Kelvin
Units for Entropy
J/K
second law of thermodynamics
the entropy of the universe increase for any spontaneous process
a specific arragnment of atoms in a substance that depends on their positioning and their kinetic energies
Microstates
Boltzmans equation
S = k*ln(Wfinal/Winitial)
k= 1.38*10^-23`
Entropy — with increasing number of microstates
increases
What are five things that will increase the value of Entropy
- increase temp
- increase volume
- increase in the number of molecules
- a solid being mixed with a liquid to form an aqueous solution
- a solid undergoing sublimation
What are the three molecular motions a real substance will perform?
Translational
Vibrational
Rotation
Translation molecular motion
whole molecule moves in one direction
seen in macroscopic objects
Rotational molecular motion
the molecule rotates about an axis
cant be done with single atoms
Vibrational molecular motion
molecules periodically move towards and away from each other
cant be done with single atoms, need more than one
Third law of thermodynamics
A perfect crystalline solid has an entropy of 0
bc it has one microstate (ln1=0)
equation to find G under standard conditions
deltaG= deltaH-TdeltaS
if G>0…
the system is non spontaneous
and spontaneous in the reverse direction
if G<0…
the system is spontaneous
if G=0…
the system is in equlibrium
in any spontaneous process (at constant P and T) free energy—
decreases
how much work can be done if a process is done 100% efficently
state function
Gibbs free energy
equation to find G under nonstandard conditions
deltaG= Gstandard formation+RTln(Q)
equation to solve for K under non standard conditions
K=e^-Gstandard formation/RT
