Acids and Bases
Classifying Acids and Bases
Electrolytes are substances that form ions in solution (via ionisation or dissociation)
All substances can be categorised into one of the three strengths:
Strong electrolytes ⇒ will fully form ions in solution (strong acids and ionic substances)
Weak electrolytes ⇒ will partially form ions in solution (weak acids and NH₃)
Non-electrolytes ⇒ will not form any ions in solution (most covalent molecular substances (excluding acids or NH₃))
What's the Difference Between Ionisation and Dissociation
Ionisation occurs when covalent bonds (in covalent compounds) are broken to form ions in solution (e.g. HCl 🠒 H⁺ + Cl⁻)
Dissociation occurs when ionic bonds (in electrovalent or ionic compounds) are broken to form ions in solution (e.g. NaOH 🠒 Na⁺ + Cl⁻)
Acid and Base Strength
Acid/Base Strength is effectively the extent to which the substance will dissociate/ionise
A strong acid fully ionises in solution
A weak acid partially ionises in solution
A strong base fully reacts with water to form OH⁻
A weak base partially reacts with water to form OH⁻
Monoprotic and Polyprotic Acids
Some acids are able to donate multiple protons (H⁺ ions), these are called "polyprotic acids"
An Acid molecule contains a polar bond between a hydrogen atom and an electronegative atom. This bond is disrupted when the acid is added to water, producing a H⁺ ion.
A monoprotic acid contains just one of these bonds, as such it only produces one H⁺ ion when added to water.
Diprotic acids (such as H2SO4) contain two of these bonds, producing two H⁺ ions, while Triprotic acids produce three H⁺ ions.
any ionic substance that does not contain H⁺, OH⁻ or O2⁻
an ionic product derived in an acid-base reaction
Salts may be neutral, acidic or basic
neutral salts are formed from the reaction between a strong acid and a strong base; they do not hydrolyse in water
basic salts are formed from the reaction between a strong base and a weak acid; they undergo hydrolysis to produce a basic solution
acidic salts are formed from the reaction between a strong acid and a weak base; they undergo hydrolysis to produce an acidic solution
Amphoteric and Amphiprotic Substances
Amphoteric substances are molecules or ions that are able to react with acids and bases.
Amphiprotic salts are ionic substances that can act as an acid or a base.
For example: HCO3⁻ (an amphiprotic salt) can react with the Water (an amphoteric substance) as either an acid or a base
Acting as an acid, HCO3⁻ reacts with H₂O to produce a HCO⁻ ion and a H₃O⁺ion
Acting as a base, HCO3⁻ reacts with H₂O to produce H₂CO₃⁻ and an OH⁻ ion