AP Chemistry Final & Exam Review

What is density?

• The mass of a given volume of matter

• D = m/v

What is atomic mass?

The number of protons plus the number of neutrons

What are isotopes?

Different versions of atoms of the same element that have the same number of protons but different number of neutrons and therefore have different atomic masses (the atomic mass listed on the periodic table is the weighted average atomic mass of all isotopes)

How do you calculate the average atomic mass of an element?

Average atomic mass = (mass)(abundance) + (mass)(abundance) …

How can you convert between moles and atoms/molecules?

By multiplying by Avagadro’s number: 1 mole = 6.02 × 10²3 atoms/molecules

What is percent composition?

The total moar mass of one type of element in a compound divided by the total molar mass of the compound

Ex: What is the percent composition of each element in SrCl2?

Sr: 1 × 87.62 =87.62 87.62/158.52 × 100% =55.3% Sr

Cl: 2 × 35.45 = 70.9. 70.9/158.52 × 100% = 44.7% Cl

What is empirical formula?

The simplest, reduced formula for a compound

What is the molecular formula?

The formula for the compound that is actually found

What is the equation for percent yield?

Percent yield = (actual mass / theoretical mass) x 100%

Percent yield will always be equal or less than 100%

What is the excess reactant (ER)?

The reactant with the greater amount of moles

What is the limiting reactant?

The reactant with the smaller amount of moles

How can you find the mass of the excess reactant remaining?

Mass of ER remaining = given mass of ER - mass of ER used

What is pressure?

The amount of force exerted on a surface due to collisions by gas particles. Can be expressed in atm, MMSG, or kPa

What is Boyle’s Law?

• P1V1 = P2V2

• Pressure and volume are inversely related at a constant temperature

• Pressure and volume can be measured in any consistent unit

What is Charle’s Law?

• V1 / T1 = V2 / T2

• Volume and temperature are proportionally related

• Temperature must be measured in Kelvin

What is Gay-Lusscac’s Law?

• P1 / T1 = P2 / T2

• Pressure and temperature are proportionally related

• Temperature must be in Kelvin

What is the equation for molarity?

C = n/v

What is another word for solution?

Homogenous mixture

What is a solute?

The substance that is dissolved

What is a solvent?

The substance that does the dissolving (often water)

What is concentration/molarity?

The amount of solute in a given amount of solution

What is solubility?

The amount of solute that will dissolve in a solvent at a given temperature to form a saturated solution

Saturated:

A solution in which no more solute can be dissolved

Unsaturated:

A solution in which more solute can be dissolved

What is a reversible chemical process?

Chemical process that can proceed in either direction such that the reactants can form products and products can form reactants

What is equilibrium?

Both the forward reaction and the reverse reaction are occurring simultaneously with the forward reaction rate equal to the reverse reaction rate.

What are some of the factors that can cause the forward and reverse reaction to “fall out of balance” and not be at equilibrium?

• Changing the concentration of a product/reactant

• Change in temperature

• Change in volume/pressure

If the pressure is increase (volume is decrease), which side will the equilibrium shift?

Towards the side with fewer molecules

If pressure is decrease (volume is increased), which side will the equilibrium shift toward?

The side with more molecules

What does a catalyst do in a reaction?

It does not shift the position of equilibrium but the reaction will establish equilibrium more quickly with the addition of a catalyst

Which is faster when the equilibrium is shift toward the right (products): the forward reaction or the reverse reaction?

The forward reaction is faster than the reverse reaction until a new state of equilibrium is reached

How can K be calculated?

K is calculated from the concentrations of each chemical at equilibrium

What does equilibrium favor when K>1? What does equilibrium favor when K<1?

• When K>1, equilibrium favors products

• When K<1, equilibrium favors reactants

What factors can change the value of K (equilibrium constant)?

A change in temperature is the only factor that can change the value of K. Increase/decrease in concentration, pressure, or volume will NOT effect the value of K.

Will K increase or decrease for an endothermic reaction (+ΔH)?

The value of K will increase with the increasing temperature in an endothermic reaction

Will the value of K increase or decreased for an exothermic reaction (-ΔH)?

The value of K will decrease with increasing temperature in an exothermic reaction

What is Q and how is it calculated?

The reaction quotient, Q, is calculated using the initial/non-equilibrium concentrations

Describe the shift of the reaction for the following conditions:

• Q = K

• Q > K

• Q < K

• When Q = K, the reaction is at equilibrium, so no shift will occur

• When Q > K, the reaction will shift left (to decease the concentration of the products and increase the concentration of the reactants)

• When Q < K, the reaction will shift left right (to increase the concentration of the products and decrease the concentration of the reactants)

How do you calculate the percent change in concentration?

Percent change in concentration = (change in concentration / initial concentration) x 100%

What is validity?

Used to check assumptions (x is negligible), percent change of concentration must be < 5% for assumption to valid

How can you calculate the resulting equilibrium constant is the equilibrium is multiplied by a number?

By raising the original equilibrium constant to that number as a power

How can you calculate the resulting equilibrium constant if an equilibrium is reversed?

The value of the resulting equilibrium constant is found by taking the reciprocal of the original equilibrium constant

How can you calculate the resulting equilibrium constant.if the two equilibriums are added to give a new equilibrium reaction?

The values of the original equilibrium constants for both reactions are multiplied to obtain the new equilibrium constant for the new equilibrium reaction

What is solubility?

The amount fo solute that will dissolve in a solvent at a given temperature to form a saturated solution

What is a unsaturated solution?

A solution in which more solute can be dissolved

What is a saturated solution?

A solution in which no more solution can be dissolved and excess solute in a supersaturated solution will form a precipitate

A solute with a high solubility (soluble salt) will result in equilibrium that favors the products or the reactants? What happens to the solid salt as a result?

Equilibrium will favor the products and all of the solid salt is converted to ions

A solute with low solubility will result in an equilibrium that favors the products or reactants? What happens to the solid salt as a result?

The equilibrium will favor the reactants, so it will only undergo a small amount of dissociation in water and only a small amount of the salt will be converted to ions, resulting in a solid in solution as a precipitate.

What is a saturated solution an indicator of?

A saturated solution indicates the solution is at equilibrium

What is solubility defined as?

The maximum number of solute that will dissolve in water, such that at equilibrium there will be no excess solid remaining so the equilibrium concentration of the salt should be 0

What is the degree of dissociation for soluble salts?

100% (soluble salts completely dissociate in water)

Are soluble ionic salts strong or weak electrolytes? Why?

Soluble ionic salts that dissociate completely in water are strong electrolytes because they efficiently conduct an electrical current.

What effect does changing the volume of a saturated solution have on molarity solubility and ion concentration?

None because molar solubility and ion concentration in a saturated solution are independent of volume

If all the solutes dissolve to give the same number of ions, how can you determine which solute has the highest solubility?

The solute with the highest Ksp value will have the highest solubility

What is the common ion effect?

It describes the decrease in solubility of a compound that results from dissolving the compound in a solvent that contains one of the ions in that compound

Will the presence of a common ion increase or decrease the solubility of a salt?

It will decrease the solubility of a salt

What is the formula equation?

A balanced double replacement reaction labeled soluble compounds as “aq” and insoluble compounds as “s”

What is the complete ionic equation?

All aq compounds are dissociated and solid compounds remain undissociated

What is the net ionic equation?

Identical ions are cancelled

What are spectator ions?

Ions that do not participate in the reaction

What are SNAP ions?

Ions that are always soluble in water. This includes Na, K, NH3, and NO3.

How can you determine if a precipitate forms?

To determine if a precipitate will form, calculate Q.

• If Q > Ksp, ion concentrations are high enough for a precipitate to form

• If Q < Ksp, ion concentrations are NOT high enough for a precipitate to form (use dilution formula: C1V1 = C2V2)

What is selective precipitation?

If the ions in the solution precipites with the same ions, relative solubility can be used to separate them. The ion present that requires a lower concentration of added ion will be precipitated first.

What is pH?

A measure of acidity of a solution. The lower the pH, the more acidic the solution is.

When is a solution considered to be acidic?

When pH<7 and [H⁺] > [OH^-]

When a solution considered to be basic?

When pH > 7 and [H⁺] < [OH^-]

What is pOH?

A measure of basicity/alkalinity of a solution: the lower the pOH, the more basic the solution is

What are some of the equations used for strong acids and strong bases?

• pH = -log[H⁺]

• [H⁺] = 10^-pH

• pH + pOH = 14

• pOH = -log[OH^-]

• [OH^-] = 10^-pOH

• 1.0 × 10^-14 = [H⁺][OH^-]

Do strong acids and bases completely dissociate in water?

YEs

List the strong acids:

• HCl

• HBr

• HI

• HClO₄

• HNO₃

• HIO₄

• H₂SO₄

• HClO₃

List the strong bases:

• LiOH

• NaOH

• KOH

• RbOH

• CsOH

• Ba(OH)₂

• Sr(OH)₂

• Ca(OH)₂

How do significant figures work in pH and pOH?

When calculating pH and pOH, only the digits after the decimal place are significant

Describe the 4 parts of the Bronsted-Lowry Model (acid, base, conjugate acid, and conjugate base)

• Acid: proton (H⁺) donor

• Base: proton (H⁺) acceptor

• Conjugate acid: has one more proton

• Conjugate base: has one fewer proton

Do weak acids or weak bases completely dissociate in water?

No, instead they form equilibrium with water

Weak Acid: HA (aq) + H₂O (l) ←→ H₃O⁺ (aq) + A^- (aq)

K_a = ( [H₃O⁺][A^-] ) / [HA]

Weak Base: B (aq) + H₂O (l) ←→ OH^- (aq) + BH⁺ (aq)

K_b = ( [OH^-][BH⁺] ) / [B]

How can you calculate pKa/pKb and K_a/K_b conversions?

• pKa = -log(K_a)

• K_a = 10^-pKa

• pK_b = -log(K_b)

• K_b = 10^-pKb

What is the equation for percent change in concentration?

Percent change in concentration = (change in concentration (x) / initial concentration) x 100%

What is percent dissociation / percent ionization?

A measure of the degree of dissociation

What is the percent dissociation/ionization for strong acids and bases?

100%

How can you determine the percent dissociation/ionization for weak acids and bases?

By using an ICE table and the equation percent dissociation = (amount dissociated (x) / initial concentration) x 100%

Which would have a lower pH (with the same initial concentration): a solution of a strong acid or a weak acid?

A solution of a strong acid

Which would have a lower concentration with the same pH: a solution of a strong acid or a weak acid?

A solution of a strong acid will have a much lower concentration than a solution of a weak acid with the same pH

What does amphoteric mean?

A compound that can act as an acid or base

Describe water’s autoionization (self ionization) process:

Water is amphoteric and undergoes autoionization (self ionization) such that some water molecules act as acids and some will act as bases according to this equation:

H₂O (l) + H₂O (l) ←→ H₃O⁺ (aq) + OH^- (aq)

This process produces both hydronium and hydroxide at equal concentrations ( [H₃O⁺] = [OH^-] ) , so the resulting solution is neutral.

The equilibrium expression is K_w = 1.0 × 10^-14 or pKw = 14

What must be true for a solution to be neutral at non-standard temperatures?

[H₃O⁺] = [OH^-], not that pH = 7

Is the autoionization of water an endothermic or exothermic process? How does this affect the value of K_w, [H⁺], [OH^-], and pH?

It is an Endothermic process, such that at higher temperatures, equilibrium shifts right and the value of Kw increases. Since Kw increased with temperature, [H⁺] and [OH^-] in a neutral solution will increase as well, and the pH of a neutral solution will decrease with the higher temperature

Is pH + pOH = 14 always true? When does it apply?

pH + pOH = 14 only applies to solutions at 25 degrees celcius, the more general equation that is always true is pH + pOH = pKw

What is the equation that related the acid dissociation constant, the bas dissociation constant, and the dissociation constant of water?

K_a x K_b = K_w. This equation can be rewritten as pKa + pKb = 14.00

The stronger the acid, the _______ its conjugate base. The stronger the base, the ______ its conjugate acid

• Weaker

• Weaker

What are some other amphoteric substances?

• HCO₃^-

• HSO₄^-

• HSO₃^-

• H₂PO₄

• HPO₄^2-

• HS^-

What happens to the equilibrium constant if you reverse the equilibrium in a weak acid and weak base equilibrium? If you add the equilibria to get the overall equilibrium?

• If an equilibrium is reversed, the reciprocal of the equilibrium constant is taken

• When you add the equilibria to get the overall equilibrium, multiply K by each of the reactions (multiple equilibrium constants together)

Which acid significantly contributes in a mixture of acids?

In a mixture of acids, only the strongest acid will significantly contribute to the concentration of hydronium ions and the pH

Which base significantly contributes in a mixture of bases?

In a mixture of bases, only the strongest base will significantly contribute to the concentration of hydroxide ions and the pOH

Which side will the equilibrium be shifted toward to in the presence of a common ion (when the concentration of the conjugate ion is not zero)?

The equilibrium is shifted to the left, decreasing the concentration of H₃O⁺ or OH^- in the presence of a common ion

Will cations found in strong bases hydrolyze?

No

Will cations that are conjugate acids of weak bases hydrolyze?

Yes, they will hydrolyze (react with water) to produce an acidic solution

Will anions found in strong acids hydrolyze?

No

Will anions that are conjugate bases of weak acids hydrolyze?

Yes, they will hydrolyze to produce a basic solution

What happens if neither the cation or anion hydrolyzes?

The solution will be neutral

What happens if both the anion and cation hydrolyze?

The Ka and Kb values for the resulting equilibria must be compared

How do you calculate the pH and pOH of a salt where both the anion and cation hydrolyze?

An ICE table is used to determine the [OH^-] from the conjugate base and the [H₃O⁺] from the conjugate acid. The ion in excess can then be used to calculate the pOH/pH of the solution