Ap Chem Thou Shalt Not Forget

Compounds can be separated into elements by

chemical changes

Mixtures can be separated by

physical changes

Filtering separates mixtures

based on differences in particle size

Distillation separates mixtures based on

differences in boiling point

Chromatography separates mixtures based on

differences in polarity

In paper chromatography,

the component that is most similar in polarity to the "mobile phase" moves up

the farthest.

Mass is conserved during

chemical and physical changes

When reading a volume of a liquid in a container, you can estimate by

reading in between the graduated

markings. That can give you one more sig. fig. in your volume.

Ranking measuring devices from least precise to most precise→

beaker, graduated cylinder, volumetric

flasks, burette

The volumetric flask has ____ on it to measure _____.

only ONE line; one specific volume.

Density =

mass/volume

The % composition by mass for a pure compound

does not change

Oxidation #'s:

H = +1 (except in a hydride when it is -1) O = −2 (except in a peroxide when it is -1).

LEO goes GER

OIL RIG

Losing electrons is oxidation. Gaining electrons is reduction.

Oxidation is loss

Reduction is gain

oxidation occurs at the

Anode (AN OX)

reduction occurs at the

Cathode (RED CAT)

Electrons in a battery flow from

anode (−) to cathode (+).

Salt bridge: Cations flow to the _____, and the anions flow to the ______.

cathode; anode.

the cathode ____ mass and the anode _____ mass.

gains; loses

(Eo): If you reverse a reaction

if you double a reaction

the sign of Eo cell changes; Eo cell DOES NOT change!!

Eo cell = (volts)

Eo cell = (volts)

Eo Red (GER) - Eo Red (LEO)

Eo Reduction + Eo Oxidation

The half-reaction with a more (+) Eo Red (more volts - winner)

is the reaction that takes place at the cathode...GER.

The half-reaction with a more (-) Eo Red (less volts - loser)

is the reaction that takes place at the anode...LEO.

When adding the two half reactions together, the electrons MUST _____________

cancel out

ΔGo =

= -n F Eo

= -(# of electrons transferred)(F constant)(Ecell)

If ΔGo is (−)

then Eo cell is (+)

(electrochem) If Q increases

then the voltage (Eo cell) of the battery goes down.

Electroplating/Electrolysis Calculation:

grams =

(Molar Mass of the metal) (amps)(seconds)/(n)(F)

=(MM)(I)(t)/nF

Thermodynamically favorable (spontaneous) reactions have a

(−)ΔG.

Reactions with (−)ΔH and (+)ΔS are ALWAYS ____________

thermodynamically favorable

"enthalpy driven & entropy driven"

Reactions that increase the # of moles of gas have a

(+)ΔS.

If ΔG is (−)

then Keq >1.

ΔH and ΔS are usually _________

NOT given in the same units!!

When using ΔGo =ΔHo−TΔSo, make sure they match units.

ΔG = 0

at equilibrium (ΔG)

When using ΔGo = −RT lnK, the R is _________________ so ΔG will be in the units of

8.314 J/mol K

Joules.

Sometimes a reaction with a (−)ΔG does not proceed at a measurable rate. They are said to be __________. _______________ is a common reason for a process to be _______________________.

under "kinetic control."; High activation energy; under kinetic control.

Exothermic reactions:

(-) ΔH; heat is a product; temp increases

Endothermic reactions:

(+) ΔH; heat is a reactant; temp decreases

ΔHrxn =

Bonds broken − Bonds formed (reactant bonds are broken; product bonds are formed)

Breaking bonds is ________

Forming bonds is _________

endothermic (takes to break)

exothermic (frees to form)

ΔHrxn=

ΔHproducts− ΔHreactants

(Don't forget to multiply by the coefficients!!)

(bonds) if a reaction is exothermic

produc bonds are stronger/more stable than the

reactant bonds.

ΔH:

a) doubling a reaction

b) revering a reaction

c) adding reactions

a) ΔH will double.

b) The sign for ΔH changes.

c)Add the ΔH's.

Buffers are created by

by a weak acid + CB (salt) or by a weak base + CA (salt).

[H+] =

MaKa / [salt]

You can use # of moles instead of molarity in this formula.

Adding a common ion to a weak acid (or base)

decreases the % ionization & therefore the pH gets closer to 7.

(at the equivalence point) MaVa=

MbVb (at the equivalence point)

M1V1=

M2V2=

Titrations: Weak acid + Strong Base has a pH at the equivalence point

(titrations) that's above 7

Titrations: Weak Base + Strong Acid has a pH at the equivalence point that's

(titrations) below 7

Titrations: Strong Acid + Strong Base has a pH ______ at

the equivalence point.

(Titrations) at 7

(1⁄2 equivalence point for a "weak + strong" titration.) pH=

=pKa & [HA]=[A-]

More buffer capacity=

more moles of weak acid/weak base & CB/CA

Solubility Equilibrium: 2 ions

Ksp= X^2

Solubility Equilibrium: 3 ions

Ksp = 4X^3

Solubility Equilibrium: "x" =

molar solubility in units of moles/liters

the larger the "x vaule"

the more soluble the salt is

if Q> Ksp

precipitate will form

Always soluble in water - usually the spectator ions

sodium Na

nitrate NO3-

ammonium NH4+ potassium K

& Group I cations

The pH of acids are

less than 7

the pH of bases are

greater than 7

the pH of pure water is only ___ at ___

7; a temperature of 25 C

Brønsted-Lowry acids

donate [H+]

Brønsted-Lowry bases

accept [H+]

Hydronium ion is

[H3O+]

[H+] is a

proton

Strong Bases

Group 1 hydroxides & Group 2 hydroxides (Some Group II hydroxides are only slightly

soluble, but whatever dissolves can completely ionize.)

Strong acids

HNO3 - Nitric

H2SO4 - Sulfuric

HClO4 - Perchloric

HBr - Hydrobromic

HI - Hydroiodic

HCl - Hydrochloric

pH=

-log[H+]

[H+]=

10^-pH

The weaker an acid/base

The stronger the conjugate base/acid

The stronger the acid/base

The weaker the conjugate base/acid

Acid-Base reactions favor the direction of

the strong side

(k>1 ~ reactants strong)

(k<1 ~ products strong)

"x" in the ice box calculation is

[H+] for a weak acid & [OH−] for a weak base.

% Ionization of a weak acid =

[H+] / Ma

% ionization increases as

acid concentration decreases (adding more water increases the amount of ionization)

if a salt contains a conjugate base of a weak acid

the salt is going to be slightly basic basic

(CBOWA's are (-) ions.)

if a salt contains a conjugate of a weak base

the salt is going to be slightly acidic

(CAOWB's are (+) ions.)

If a salt contains conjugates of strong acid/bases

the ion is neutral. ex: KBr is a neutral salt (KOH

+ HBr)

A larger Ka value means

a stronger acid

A larger Kb value means

a stronger base

Relative strengths of acids:

a. smaller cations are

b. more (+) charge on a cation

c. more oxygens (or electronegative atoms) on an anions make it

a. more acidic

b. more acidic

c. more acidic since the proton is more ionizable

Keq =

[products]^x

/[reactants]^y

x and y represent the coefficients in the balanced chemical equation.

Only states of matter that appear in an equilibrium expression:

(aq) & (g)

equilibrium expression: brackets

[molarity]

equilibrium expression: paratheses

(Pgas) - atm

Large Keq

more products at equilibrium

small Keq

more reactants at equilibrium

Reversing a reaction

1/Keq

doubling a reaction

(Keq)^2

Adding reactions

Multiply the K's together

Le Chatelier's Principle:

States that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress.

If Q >Keq

reaction shifts to the left: toward the reactants

Q < Keq

then the reaction shifts to the right: toward the products

Catalysts and inert gases __________ an equilibrium

Do NOT shift

Changes in pressure (by changing volume of a container) can shift an equilibrium ONLY IF

The number of moles of gas particles are different on each side

An increase in pressure favors a shift in the equilibrium towards

the side with less moles of gas (volume decrease, pressure increase)

In order for a reaction to occur:

- particles must collide

- at the correct orientation

- with a minimum energy to break bonds (activation energy)

How to write a rate law for an elementary step:

2A + B → C + D

Rate =k[A]^2 [B]^1

Rate constant (k) Units:

1st order = s^-1

2nd order = M^-1 s^-1