Chemistry Quiz 3

What is the common ion effect?

Addition of a salt to suppress the ionization of a weak acid or base

What makes up a buffer solution

- Weak acid and its conjugate base

- Weak base and its conjugate acid

What is the Henderson equation?

pH = pKa + log [A-]/[HA]

Strong Acid + Strong Base Titration Curve

- Equivalence Point/pH = 7

- Graph starts around 1

Weak Acid + Strong Base Titration Curve

- Equivalence Point/pH > 7

- Graph starts above 1

Weak Base + Strong Acid Titration Curve

- Equivalence Point/pH < 7

- Starts below 1

What are buffers?

Substances that minimize changes in pH even with exposure to acids and bases

How do you pick a buffer?

The best buffer has a pKa +/- 1 of the target pH

What is your pH at the half equivalence point?

pH = pKa

Formation Constant (Kf)

The rate of the forward reaction

Kf = products/reactants (reactants are usually a metal and a ligand)

Solubility Product Constant (Ksp)

The equilibrium constant for the dissolution of a solid to aqueous ions

Ksp = reactants (no products because its a solid)

When do you use formation constant (Kf)?

When forming a complex ion

- A (aq) + B (aq) -> AB (aq)/(s)

When do you use solubility product constant?

When you dissolve a solid to make soluble ions

- AB (s) -> A (aq) + B (aq)

What is precipitation?

Whenever we form a solid

- Use Q to do this

What happens when Q is greater than Ksp?

Precipitation happens because reaction goes to the left (reverse direction)

What happens if Q < Ksp?

No precipitation will happen because the reaction will go to the right (forward direction)

Selective Precipitation

If two possible complexes share an ion, one will precipitate first

- usually the complex that is the least soluble (smallest Ksp)

What is a spontaneous process?

A process that moves a reaction system toward equilibrium

Entropy (triangle S)

Disorder or randomness

- Increased by heat or vibration

How do you find entropy?

Sum of products - sum of reactants

Gibbs Free Energy

The energy of a system that is available to do work at a constant temperature and pressure

- G = H - TS (add the triangles if it is the change)

Gibbs Free Energy + Spontaneous

G < 0 = spontaneous

G > 0 = not spontaneous

G = 0 = at equilibrium

Entropy + Spontaneous

S < 0 = not spontaneous (endo)

S > 0 = spontaneous (exo)

S = 0 = at equilibrium

Enthalpy + Spontaneous

H < 0 = spontaneous (exo)

H > 0 = not spontaneous (endo)

H = 0 = at equilibrium

How to find the equilibrium value of G?

Triangle G^0 = sum of products - sum of reactants

What is a salt bridge and wire ?

Salt Bridge - Channel that ions pass through

Wore - Pathway for electrons

How does the complete circuit for an electrical system work?

Electrons pass through the wire and the charges balance as the ions pass through the salt bridge

What are the two electrodes?

Anode = oxidation (losing electrons)

Cathode = reduction (gaining electrons)

Cell Potential (E)

Driving force of an electrochemical cell

- Sum of two half reactions of an anode and cathode

Voltaic/Galvanic Cell

A spontaneous electrochemical cell

How do you make a reaction go if not spontaneous?

Heat the reaction up

- ex. electrolytic cell uses heat to push a reaction against its potential

What does +E mean?

The cell is spontaneous

- If E < 0 = not spontaneous