Equilibrium

What happens when a salt is added to water?

The salt begins to dissolve, and ions precipitate.

What are the three types of solutions based on saturation?

Unsaturated, saturated, and supersaturated.

What is the equilibrium reaction for a saturated salt solution?

AB (s) ⇌ A⁺ (aq) + B⁻ (aq).

What is the solubility product constant (Ksp)?

Ksp = [A⁺]^coefficient[B⁻]^coefficient, representing the equilibrium constant for a saturated solution.

How can a saturated solution be established?

By starting with excess salt and dissolving until saturation is reached, or by mixing two salt solutions that precipitate.

What is the significance of dynamic equilibrium in a saturated solution?

The dissolved ions form an equilibrium with the precipitated crystals.

How is molar solubility defined?

It is the maximum amount of an ionic compound that will dissolve in a given volume of solvent at a specific temperature.

What does the reaction quotient (Q) indicate?

Q is used to predict whether a precipitate will form when mixing solutions of metal cations and non-metal anions.

What does it mean if Q < Ksp?

No precipitation occurs because there are fewer ions present than needed to saturate.

What does it mean if Q = Ksp?

The solution is saturated, and no precipitation occurs.

What does it mean if Q > Ksp?

The solution is supersaturated, and a precipitate will form.

Weak Acid

Does not completely ionize in water.

Weak Base

Does not completely dissociate in water.

Percent Ionization

Percentage of acid that ionizes in solution.

Ionization Constant (Ka)

Equilibrium constant for weak acid ionization.

Kw formula with Ka and Kb

Kw = ka kb

If we know _, we can calculate the percent ionization

The pH of the weak acid

The percent dissociation of a weak acid (HA) in terms of hydrogen ion concentration ([H+]) and the acid concentration ([HA]

[H+(aq)] = P /100 x [HA(aq)]

Percent ionization formula

P = [ M of acid ionized / M of acid solute ] x 100%

pH of weak acids tends to be closer to ___, whereas strong acids read ___

7, a much lower number

Most weak acids ionize at less than _%

50% (only 50% of the compound split into ions)

Polyprotic acid

have more then one ionizable hydrogen- this means they will ionize in a multi-step process, and each step will have its own Ka

Kw value

1.0 x 10^-14

Acids ____ in water to produce ___

ionize, hydrogen ions

Ionize - makes ____ from molecules that were _____

ions, not ionic

Bases ____ in water to form ___

dissociate, hydroxide ions

Dissociate- separates ___ of ___ molecules

ions, ionic

Acids are proton ___. Bases are proton ____.

donors (give away H+), acceptors (receive the H+)

Amphiprotic/Amphoteric

Amphiprotic/Amphoteric compound is a molecule or ion that can react both as an acid as well as a base. (Ex. Water)

Completely IONIZES in water (not an equilibrium because K is huge)

Strong acid

All OH- containing salts are strong bases (they have different solubility, but the amounts that do dissolve, completely dissociate… Not true equilibrium)

Strong bases

Conjugate acid

an acid that forms when a base gains a proton

Conjugate base

a base that forms when an acid loses a proton

pH formula

pH=-log[H+]

pOH formula

pOH=-log[OH-]

H+ formula

[H+] = 10^-pH

[OH-] formula

10^-pOH

6 strong bases

LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

or

Lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide

8 strong acids

HCl, HBr, HI, HClO4, HNO3, HIO4, H2SO4, HClO3

or

Hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, nitric acid, periodic acid, sulfuric acid, chloric acid

Strong or weak acid: HCl

Strong

Strong or weak acid: CH3COOH

Weak

Strong or weak acid: HI

Strong

Strong or weak acid: HF

Weak

Strong or weak acid: H2O

Weak

Strong or weak acid: HClO3

Strong

Strong or weak acid: H2S

Weak

Strong or weak acid: H2SO4

Strong

What happens after the equivalence point in a titration?

There is excess strong base or strong acid present.

How do you calculate pH after the equivalence point with excess strong base?

Calculate [OH-] directly, then use pOH to find pH.

How do you calculate pH after the equivalence point with excess strong acid?

Calculate [H+] directly and use pH = -log[H+].

What should you use if you're dealing with a weak acid before or at the start of a titration?

Use the acid dissociation constant, Ka.

What is the significance of the equivalence point in a titration?

It's the point where the original acid or base is no longer present; only the conjugate salt remains. Mols are equal.

What type of salt is formed from a strong acid and strong base?

Neutral salt (e.g., NaCl).

What type of salt is formed from a weak acid and strong base?

Basic salt (e.g., NaC₂H₃O₂, KCIO).

What type of salt is formed from a strong acid and weak base?

Acidic salt (e.g., NH₄Cl).

What do you use in the buffer region before the equivalence point?

Use Ka if the solution contains a weak acid; use Kb if it contains a weak base.

What is the pH when there is no hydrolysis occurring?

pH = 7

What constant is used for anion hydrolysis?

Use Kb derived from Ka.

What constant is used for cation hydrolysis?

Use Ka derived from Kb.

What is the first step in analyzing a titration?

Determine if a weak acid or base is present.

Weak acid strong base at equivalence

Anion hydrolysis (produces OH)

Weak base strong acid at equivalence

Cation hydrolysis (produces H3O)

Strong base strong acid at equivalence

No hydrolysis

Magnitude of K

Shows how much the reaction has gone to completion when equilibrium is reached.

Heterogeneous Equilibria

Equilibria involving different forms of matter (ex. liquid, gas or aqueous, solid)

Homogeneous Equilibria

Equilibria with reactants and products in same form (ex. all gasses)

Concentration of Pure Liquid

= 0; does not change in equilibrium.

Q = K

Indicates system is at equilibrium.

Q < K

Products need to increase to reach equilibrium. More reactants present. Therefore reactants are negative

Q > K

Products need to decrease to reach equilibrium. More products present. Therefore products are negative

Small K Simplification / 100 Rule

When K is at least 100 times smaller than the non-zero initial concentration, x becomes negligible and can be interpreted as "0" with significance.

Perfect Square Simplification

Used when reaction yields perfect square results; does not need quadratic formula. Solved via basic algebra.

Quadratic Equation

Used for solving equilibrium concentrations when necessary.

Equilibrium Expression

When given aA + bB -> cC + dD: K= [C]^c[D]^d/[A]^a[B]^b

Example of K Calculation

K = [products]^[coefficients] / [reactants]^[coefficients].

K Value Interpretation

High K indicates products favored; low K indicates reactants favored.

Equilibrium Shift Direction

Determined by comparing Q and K values.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [N₂] is increased

N2 ⬆ H2 ⬇ NH3 ⬆. Shifts the equilibrium to the right. Products.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [H₂] is increased

N2 ⬇ H2 ⬆ NH3 ⬆. Shifts the equilibrium to the right. Products.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [NH₃] is increased

N2 ⬆ H2 ⬆ NH3 ⬆ Shifts the equilibrium to the left. Reactants.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; Temp is increased

N2 ⬆ H2 ⬆ NH3 ⬇ Shifts the equilibrium to the left. Reactants.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [N₂] is decreased

N2 ⬇ H2 ⬆ NH3 ⬆. Shifts the equilibrium to the left. Reactants.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [H₂] is decreased

N2 ⬆ H2 ⬇ NH3 ⬇ Shifts the equilibrium to the left. Reactants.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; [NH₃] is decreased

N2 ⬇ H2 ⬇ NH3 ⬇ Shifts the equilibrium to the Right. Products.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; Temp is decreased

N2 ⬇ H2 ⬇ NH3 ⬆ Shifts the equilibrium to the right. Products.

N₂ (g) + 3H₂ (g) <-> 2NH₃ (g) + 92kJ; A catalyst is added

Does not shift the equilibrium.

Ka =

[H⁺] [A^-] / [HA] or [H₃O⁺] [A^-} / [HA]

Kb =

[OH^-] [HB⁺] / [B]

H2O + H20 →

H₃O⁺ + OH^-

Kw =

[H₃O⁺] [OH^- ] or [H⁺] [OH^- ]

Kw is the value

14

pkw formula

14 = pOH + pH