Acids and Bases

Acid

Produces H+ in solution;

Accepts an electron pair in a reaction

Donates H+ (hydrogen proton) - Gives away H+

Base

Creates OH- in solution

Donates an electron pair in a reaction

H+ acceptor (hydrogen proton)

Is Water a Acid or a Base?

It can act as both an acid and a base! It depends on what else is present!

Conjugate Acid–Base Pairs in reactions

HCl - The Big 6

Hydrochloric acid

HBr - The Big 6

Hydrogen Bromide

HI - The Big 6

Hydrogen Iodine

HClO4 - The Big 6

Perchloric Acid

HNO3 - The Big 6

Nitric Acid

H2SO4 - The Big 6

Sulfuric Acid

Factors Affecting Acid Strength in Binary Acids

The more polar the H-X bond (the bond between hydrogen (H) and a halogen or another nonmetal (X) in a binary acid), the weaker the binary acid.
- (This means that if the difference in electronegativity between H and X is large (i.e., the bond is highly polar), the acid is weaker because the bond holds onto the hydrogen more tightly, making it harder to ionize (release H⁺ in solution).

The weaker the H-X bond, the stronger the binary acid

Factors Affecting Acid Strength in Oxoacids

H—O—Y

The more electronegative the element adjacent to the oxygen (Y), the stronger the acid

Factors Affecting Acid Strength

The more oxygen atoms in an anion, the greater stability, and the weaker the H-O-Y bond

Delocalization of the negative charge over more electronegative atoms - Stronger the acid

More oxygen atoms affect the oxidation number of adjacent elements in the polyatomic anion

The higher the oxidation number of element adjacent to oxygen, the stronger the acid. (slide 15)

pH = -log[H3O+]

Used to calculate the pH of a solution based on the concentration of hydronium ions (H₃O⁺) in moles per liter (M). It expresses the acidity of a solution on a logarithmic scale.

Kw = 1 × 10^-14 = [H3O+]*[OH-]

Degree of Ionization

Indication of Acid Strength expressed as a decimal

Ionized Acid (H+)/ Initial Acid(HA)

Percent Ionization

Degree of ionization expressed as a percentage

[Ionized Acid (H+)/ Initial Acid(HA)] * 100%

pH of Mixtures of Weak Acids (or Bases)

The pH of the strong acid alone can estimate the pH of a mixture of strong and weak acids. So if you have to estimate the PH of a mix of strong and weak acids then just use the strong acid to make that estimate

Checking the ‘x is small’ assumption

Multiply the Ka value by the initial concentration, then take the square root of the result.

Next, divide that value by the initial concentration and multiply by 100 to get a percentage.

• If the percentage is less than 5%, the assumption is valid, so you can ignore x in the denominator and skip the quadratic equation.

• If it's more than 5%, the assumption is invalid, and you need to solve using the quadratic formula.

Strong Bases

Most oxides (O2-) and hydroxides (OH-) of Groups 1 and 2 (Alkaline Metals and Alkaline Earth Metals)

Completely dissociate in solution

Weak Bases

Nitrogen-containing compounds

Do not completely dissociate from the solution

Difference between pH and pOH

Both pH and pOH measure the concentration of ions in a solution, but they focus on different aspects of acidity and basicity

• If pH = 3, then pOH = 14 - 3 = 11 (acidic solution).

• If pOH = 2, then pH = 14 - 2 = 12 (basic solution).

Relationship between Ka and Kb

Kw = Ka*Kb

If we know one, we can figure out the other one, Kw is given

Polyprotic Acids

They can donate more than one proton (H⁺) in solution

• Harder to dissociate the second proton

Diprotic Acids

Can donate two protons (H⁺)

Ka1 > Ka2

• More difficult to remove H+ ion from negatively charged anion

• Typically, only first H+ dissociation affects pH (Ka1)

Triprotic Acids

Can donate three protons (H⁺)

Ka1 >> Ka2 & Ka3

Triprotic Acids: Phosphoric Acid

Formula: H3PO4

Triprotic Acids: Citric Acid

Formula: C6H8O7

What ions are always soluble in compounds with no exceptions?

• Li⁺, Na⁺, K⁺, NH₄⁺

• NO₃⁻, C₂H₃O₂⁻

Are Cl⁻, Br⁻, and I⁻ soluble?

• Yes, generally soluble.

• Exception: Insoluble when paired with Ag⁺, Hg₂²⁺, or Pb²⁺.

Is SO₄²⁻ (sulfate) soluble?

• Yes, generally soluble.

• Exceptions: Insoluble when paired with Sr²⁺, Ba²⁺, Pb²⁺, Ag⁺, or Ca²⁺.

Are OH⁻ and S²⁻ soluble?

• Generally insoluble.

• Exceptions:

  • Soluble with Li⁺, Na⁺, K⁺, NH₄⁺.

  • S²⁻ is soluble with Ca²⁺, Sr²⁺, Ba²⁺.

  • OH⁻ is slightly soluble with Ca²⁺, Sr²⁺, Ba²⁺.

Are CO₃²⁻ (carbonate) and PO₄³⁻ (phosphate) soluble?

• Generally insoluble.

• Exception: Soluble with Li⁺, Na⁺, K⁺, NH₄⁺.