AP Exam tips!

things you don't wanna miss that are all memorization! 1. when in doubt: cancel units out/always MATCH UNITS, think back to labs/equipment in class, don't justify if you don't need to, make SMART answers! it's the same test over and over again :)

to avoid getting units or SF points off

BOX OR CIRCLE YOUR FINAL ANSWER

FRQ basics strategies

1. pick the best, most concise answer!

2. only answer stem of the problem

3. try to immediately assign topic/unit relevant to question so you can focus brain

4. UNITS and SF (be careful, check for constants)

5. think back to in class labs and examples!

there are no negative…

equilibrium constants, Kelvin temperatures, bond energies/enthalpies (energy it takes to break a bond)

drawing/modeling particle diagrams

things to consider:

states of matter, relative amounts of particles, changes to size of container, if particles will react

remember your addition and subtraction rules

ALL ABOUT # of DECIMAL PLACES not total number of digits!!

equilibrium constant (K) rules:

1. when reversing the reaction, take the inverse of the K value

2. when multiplying the reaction by a coefficient, raise the K value to the power of that coefficient

3. when adding reactions with given K values, multiply their K values for overall K

@ equilibrium all reactant and product concentrations

are CONSTANT!

this is like a key characteristic/sign you’re dealing w/ equilibrium when concentration reaches constant value

never include solids/liquids in

equilibrium constant expressions or ICE tables

as acid or base strength DECREASES

its conjugate species strength INCREASES

properties of ionic compounds

• form crystals (arranged in lattice of + / - ions)

• HIGH melting and boiling points

• low vapor pressures

• hard, BRITTLE due to repulsion of like charges caused when 1 layer slides across another layer

• conduct electricity when dissolved and molten

• good insulators as solid

properties of metals:

• metallic attractions b/c of multiple metallic cations being attracted to a delocalized sea of valence electrons

• shiny/lustrous

• malleable and ductile

• conduct heat and electricity

when listing IMF for the first time…

don’t use any abbreviations

formal charge

valence electrons - (number of lone electrons + bonds)

dilution equation!!

ViMi = VfMf

increasing vol w water will decrease concentration, increase percent ionization

relationships between Gibbs free energy, enthalpy, entropy:

ΔG = ΔH - TΔS

1. if -H and +S →spontaneous at ALL temperatures

2. if +H and -S →not spontaneous at any temp.

3. if both negative →only spontaneous @ low temp.

4. if both positive →only spontaneous @ high temp.

nernst equation

→cell potential depends on ratio of concentration/concentrations!!

Ecell = Ecell° - (0.0592/n)log Q

→Q is products over reactants

things to remember for net ionic equations

• you can only break up strong electrolytes

  • strong acids/bases, aqueous solutions, etc.

• keep everything else together!! (NEVER SEPARATE WEAK ACIDS/BASES)

• cancel out common ions

• write states of matter and correct rxn arrows

solubility rule must haves

group 1, nitrates, acetates, ammonium, perchlorate are always soluble

factors that affect entropy

1. STATE OF MATTER TAKES precedence!!

   • gas > liquid > solid

2. number of moles

3. temperature

units for free energy, entropy, enthalpy

ΔG and ΔH →usually kj/mol

ΔS →usually J/mol*K

when in doubt for units

see what cancels out!!

units of K per overall rxn order

M^1-nt^-1

any time given bond enthalpies

BIG INDICATOR FOR BONDS BROKEN - BONDS FORMED

collision theory states

for a rxn to occur: molecules must collide with sufficient energy and proper orientation

for gases: density can be found by

d = MP/RT

• M is molar mass

FOR EQUILIBRIUM

set up ice tables!!! so you don’t make basic math mistakes

when to assume rxns go to completion?

precipitation, neutralization, producing water

carbonate as an acid reaction

2H⁺ + CO₃^2- →CO₂ + H₂O

best conditions for ideal gases

HIGH temperature, LOW pressure

the only time you use 0.08206 as the value for R

is PV = nRT, otherwise check what units need to be cancelled out!

CONTAMINATION for gas collection by water displacement

either water vapor present OR other gases in the air if tube wasn’t previously evacuated

avg. KE is not the same as

avg. molecular speed!!! (molecular speed just depends on how heavy molecule is, heavier = slower)

avg. KE is directly proportional to

TEMPERATURE

key first order rxns characteristic

CONSTANT half life!! independent of concentration OR PRESSURE

• 0.693/k

beer’s law

absorbance = molar absorptivity*concentration*path length

• usually path length/molar absorptivity are held constant, so absorbance is directly proportional to concentration

  • this means their ratios are also constant!

hybridization is all about

steric number!! solely based on this

definition of equilibrium

when rates of forward and reverse reactions are equal

“justify with a calculation”

puts both units and SF on the table so double triple check!

break ionic compounds apart when

assigning oxidation numbers →makes it easier!

when asked to write Ka, Kw, Kb expressions

WRITE AS EQUALITIES

STP

1.00 atm, 273 K, 22.4 L = 1 mol

when removing electrons

ALWAYS remove electrons from VALENCE (OUTERMOST) shell →esp. remember this when writing electron configurations

buffer systems = automatic sign for

HENDY HASS!!!

always check units for enthalpy for

mol/rxns or mol/g etc. because this really affects stoichiometry of answer!!!!

taking log SF rule

however many total digits there are = number of decimal places in answer

taking antilog SF rule

however many decimal places = total number of SF in answer

wavelength usually given in units of

NANOmeters, might have to convert to cancel out!!

→1 nm = 1×10^-9 m

only one wavelength for maximum absorbance

every other wavelength used will give a lower absorbance!!

absorbance

how much light can be absorbed

• helps us measure concentration of a colored substance

• more concentrated solution = the less light that will pass through

for electromagnetic spectrum

Energy = J/photon!

be careful w/ units and alter → one of few times you may have to use avogadros number

network covalent solid

to break network covalent solid, you have to break ALL the covalent bonds which takes a lot of energy

@ equivalence point when you have to WMX

make sure you divide moles of salt by TOTAL VOLUME because you need molarities!!

calculating pH in an overtitration

treat excess titrant as strong acid/base, just get pH from this!!

[FOR ACIDS] more oxygen atoms means

a stronger acid