Chemistry - Acid/Base Equilibria

Bronsted-Lowry theory

theory that states that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base

conjugate pair

a pair of substances that only differ through a single proton that are formed in a reversible reaction between a Bronsted-Lowry acid and a Bronsted-Lowry base, where a pair consists of one of the reactants and one of the products

conjugate acid

a compound formed when a Bronsted-Lowry base accepts a proton in a reversible acid-base reaction

conjugate base

a compound formed when a Bronsted-Lowry acid donates a proton in a reversible acid-base reaction

strong acid

an acid which has a high tendency to donate its proton and fully ionizes in solution

weak acid

an acid that has a lower tendency to donate its proton and partially ionizes in solution

strong base

base that has a high tendency to accept a proton and fully ionizes in solution

weak base

that which has a lower tendency to accept a proton and partially ionizes in solution

p notation (2)

a logarithmic scale used to express chemical values simply and draw comparisons rooted in concentration

-log[number]

pH (2)

a scale that measures the concentration of hydrogen ions in a substance and is generally used to scale acidity

-log[H⁺]

pOH (2)

a scale that measures the concentration of hydroxide ions in a substance and can be used to scale acidity but rarely as hydroxide ions less evidently/relevantly relate to changes in acidity

-log[OH⁻]

Describe the pH and pOH scales (2)

pH typically follows a scale of 0-14, where lower values are more acidic and higher values are more basic

pOH typically follows a scale of 0-14, where lower values are more basic and higher values are more acidic

Kᵥᵥ (3)

an equilibrium constant that expresses the concentration of water’s ion relative to neutral water at equilibrium

[H⁺][OH⁻]

@25⁰C = 1×10⁻¹⁴

Define Kᵥᵥ in terms of pH and pOH

pKᵥᵥ = pH + pOH = 14 @25⁰C

Kₐ (2)

an equilibrium constant that expresses the equilibrium ratio of an acid’s disassociated ions to its associated form

For the reaction, HA ↔ H⁺ + A⁻, Kₐ = [H⁺][A⁻]/[HA] or [H⁺]²/[HA]

Describe how Kₐ and pKₐ scale acidity (2)

In Kₐ larger values means the acid ionizes more and is stronger

In pKₐ lower values means the acid is stronger

K₆ (2)

an equilibrium constant that expresses the equilibrium ratio of a base’s disassociated ions to its associated form

B + H₂O ↔ BH⁺ + OH⁻, Kₐ = [BH⁺][OH⁻]/[B] or [OH⁻]²/[B]

Describe how K₆ and pK₆ scale acidity (2)

Higher values of K₆ means the base ionizes more and is stronger

Lower values of pK₆ means the base is stronger

Describe Kᵥᵥ in terms of Kₐ and K₆

pKₐ + pK₆ = pKᵥᵥ

Describe this graph

pH titration curve for a strong acid being added to a strong base

Describe this graph

pH titration curve for a strong base being added to a strong acid

Describe this curve

pH titration curve for a strong acid being added to a weak base

Describe this curve

pH titration curve for a weak base being added to a strong acid

Describe this curve

pH titration curve for a weak acid being added to a strong base

Describe this curve

pH titration curve for a strong base being added to a weak acid

Describe this curve

pH titration curve for a weak acid being added to a weak base

Describe the curve

pH titration curve of a weak base being added to a weak acid

indicator

a substance which changes colour when the pH changes within a certain range of pH values

pH range of an indicator

the intermediate point between two pH values at which the indicator changes colour

Denote the pH ranges and colour changes of methyl orange, screened methyl orange, bromophenol blue, litmus and phenolphtalein

How do you choose a suitable indicator for a reaction?

The indicator must fall between the range in which the most rapid pH change occurs in the reaction

Denote the ranges of the various acid-base reactions and the suitable indicators for each (1/5/1/4/1/2/1/1)