All my love for Chem Pt.2

Arrhenius Concept

Acid - produce hydrogen ion in an aqueous solution
Base - produce hydroxide ion in an aqueous solution

Bronstead Lowry Concept

Acid - proton donor
Base - proton acceptor

Conjugate Acid & Base

Conjugate Acid - species formed when proton transferred to the base
Conjugate Base - what remains of acid molecule after proton is lost

Lewis Acid & Lewis Base

Acid - any substance that accepts a lone pair of electrons
Base - Any substance that donates a lone pair of electrons

Lewis Acid/Base Examples

Acid is usually a cation or something that has an incomplete octet or central atoms can hold more than 8 valence electrons
Base is usually anion (Polyatomic Ions)
Or unpaired electrons

Strong Acid Relative Strengths

Strong acid wants to give away proton; the more readily it wants to give it away, the strong the acid (higher dissociation)
Creates a weak C. Base
Strong Base creates weak C. Acid because it does not want to give it away

Common Strong Acids

HCl, HBr, HI, HNO3, HCLO4, H2SO4

Common Strong Bases

LiOH, KOH, NaOH, RbOH, CsOH, Sr(OH)2, Ba(OH)2

Determining Strength Using Equil Constant

Larger Ka value, stronger the acid & the weaker the base
Smaller Ka value, weaker the acid & the stronger the base

Binary Acid

acid containing hydrogen as well as nonmetallic element

Oxyacid

acid containing oxygen, hydrogen, and another element
General Formula: HnYOm
Y is a polyatomic anion that contains metal or nonmetallic atom

Binary Acid Strength

For elements in same group of periodic table: shorter bonds are stronger → directly related to atomic radius
For elements in same period of periodic table: more electronegative, stronger the acid

Oxyacid Strength

For oxyacids with same # of OH groups & same # of O atoms, acid strength increases as electronegativity of Y increases
Oxyacids with same Y atom but different # of oxygen atoms, acid strength increases as # of oxygen atoms increase

Significant difference between acid strength values

Know its significant if different by 3 order of magnitude or more for Ka values

Monoprotic

one dissociable proton

Diprotic

two dissociable protons

Calculating Polyprotic Acids

Ka gets significantly weaker (only consider 1st when calculating pH)

Relationship between Ka and Kb

Ka * Kb = Kw = 1×10^-14

Acid Base Properties of Salts

Acid + Base → Salt + H2O
Can go backwards to determine what acid/base created the salt

Salt of strong base + strong acid

No hydrolysable ions and gives neutral solution (neutral)

Salt of strong base & weak acid

Anion of salt is conjugate of weak acid so it will hydrolyze and give a basic solution (basic salt)

Salt of weak base and strong acid

Cation is conjugate of base, so it will hydrolyze and give an acidic solution (acidic salt)

Salt of weak base & weak acid

Both ions hydrolyze, so pH depends on relative acid-base strength of two ions (depends on Ka/Kb values)

Determining Salt Acidity from Weak Base and Weak Acid

Which ever value is larger, that is the ion that will dominate the equilibrium
EX: CN- > NH4+ (BASIC SOLUTION)
Kb > Ka

Acidic Buffer

Consists of weak acid and its salt (conjugate base)

Basic Buffer

Consists of a weak base and its salt (conjugate acid)

A-/HA Ratio & Buffering Capacity

The closer the A-/HA ratio is to 1, the buffering capacity increases; all solutions that have the same A/HA ratio will have the same pH

Choosing & Preparing Buffer Solutions

The best buffer solution is the one where the pKa of the weak acid is as close as possible to the desired pH

Strong Acid-Strong Base Titration regions

1. Initial pH

2. Between initial & equivalence point

3. Equivalence Point

4. After EP

Equivalence Point Equation

d²pH/dV² = 0

When pH = pKa

Vb = 1/2Vc

Weak Acid - Strong Base Titration Regions

1. Initial pH

2. Buffer region (HH equation)

3. Equivalence Point

4. After EP

Two distinct inflection points

Titration Curve Dependencies

Strength of acid/base

- As strength decreases, rapid rise decreases
- pKa > 8
Concentration of original solution
- As concentration increases, rapid rise increases
- HA EP becomes blurred when HA too diluted

Titrations in Multi-protic Systems

Starts out with low pH value
Go through titration curve multiple times

When titrating acid, how much In- must be present to detect color change

In-/HIn - 1/10

When titrating base, how much In- must be present to detect color change

In-/HIn = 10/1

Choosing Indicator

Ideally, want endpoint of indicator to be as close to EP as possible