pH, pOH, pKa

Ionization of water

Ionization of water leads to a Hydronium ion being formed (H₃O⁺) and a Hydroxide ion being formed (OH^-)

• This is when one water molecule nabs a hydrogen from another water molecule, leading to autoionization of water

How much hydronium is in one liter of water?

One litre has roughly 1×10^-7 M of hydronium

Whats a Molar (M)

M = mole/L

• This is also known as the concentration of something

How to calculate concentration of a substance?

C = mass (in moles or grams) / volume (in liters usually)

Acidic solution

The Concentration of H₃O⁺ > OH^-

Basic solution

The Concentration of H₃O⁺ < OH^-

pH

p is the -log₁₀

so pH is just the -log₁₀[H⁺]

(we use H⁺ and H₃O⁺ synonymously, they mean the same thing)

pOH

This is the -log₁₀ [ OH^- ]

pH and pOH

For any aqueous solution at 25*C pH + pOH = 14

Find concentration of H⁺ or OH^- using pH and pOH

[ H⁺ ] = 10^-pH

[ OH^- ] = 10^-pOH

Ka

This is the acid ionization constant (also known as the acid dissociation constant)

Bronsted-Lawry Base

• If a molecule is acting as a BLB, than it will accept an electron from another molecule

Bronsted-Lawry Acid

• If a molecule is acting as a BLA, then it will donate an electron to another molecule

Weak acid vs Strong acid (K_a)

• As a strong acid fully dissociates in water, it has a large K_a (greater than 1)

• Weak acids, on the other hand, do not dissociate well, thus having a small K_a (less than 1)

Weak base vs Strong base (K_b)

• As a strong base fully dissociates in water, it has a large Kb (greater than 1)

• Weak bases, on the other hand, do not dissociate well, thus having a small Kb (less than 1)

pK_a ( Applies to pK_b )

pK_a = -log[K_a]

• This, unlike K_a, is inversely related to the strength of an acid; a lower pK_a value suggests a stronger acid

% Ionization or dissociation

% = X / HA

• X represents amount of acid that was dissociated (usually the H₃O⁺ concentration and for bases its the OH^- concentration)

• HA is just the concentration of the acid or the base (on the reactant side)

Acetic acid (Weak or Strong acid)

Weak acid

Steps in solving the pH of a weak acid

1. If dissociation constant is given, firstly write the formula out

2. Then, using ICE, write the equation using K_a

3. Solve for x

   1. If K_a is small, in the denominator of the equation, you can ignore the value of X and solve it that way. Otherwise, use the quadratic formula.

4. Use the pH = -log [H⁺] to find the pH using the concentration of hydronium