Ionisation in Water
Ionisation Process: When acids and alkalis dissolve in water, they undergo a special change called ionisation. In this process, the substances break apart into two types of charged particles: positive ions and negative ions. This breaking apart into ions is what makes acids and alkalis behave the way they do, showing their special chemical properties like sourness in acids and slipperiness in alkalis.
Complete vs Partial Ionisation: Ionisation can happen in two different ways. Complete ionisation is when every single molecule in a solution splits into ions, with none left unbroken. Partial ionisation is when only some of the molecules split apart, while others stay whole and do not turn into ions. This difference affects how strong or weak the acid or alkali is.
Ionisation and Strength: The strength of an acid or an alkali depends on how much it ionises when mixed with water. Strong acids and alkalis ionise almost completely, meaning most of their molecules break apart. Weak acids and alkalis ionise only a little bit, so many molecules stay together without splitting.
Strong Acids
Definition of Strong Acids: Strong acids are special kinds of acids where almost all the acid molecules break apart completely when they are mixed with water. This complete ionisation produces a lot of free hydrogen ions (H⁺) floating around in the solution.
Characteristics of Strong Acids: Because strong acids make a lot of hydrogen ions (H⁺), they cause the solution to have a very low pH number. A low pH means the solution is very acidic and can react strongly with other substances.
Examples of Strong Acids: Some common examples of strong acids are hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃). When you put them into water, they completely split into their ions, meaning no whole acid molecules are left.
Weak Acids
Definition of Weak Acids: Weak acids are acids where only a small number of molecules break apart into ions when they dissolve in water. Most of the molecules stay together and do not form hydrogen ions (H⁺).
Characteristics of Weak Acids: Weak acids produce fewer hydrogen ions (H⁺) in the solution compared to strong acids, even if the amount of acid you add is the same. Because there are fewer hydrogen ions, weak acids have a higher pH value than strong acids.
Examples of Weak Acids: Examples of weak acids include ethanoic acid (CH₃COOH) and methanoic acid (HCOOH). In water, they create a mix where some molecules turn into ions while others stay the same, leading to a balanced state called equilibrium.
Strong Alkalis
Definition of Strong Alkalis: Strong alkalis are substances that, when dissolved in water, completely break apart into ions, especially forming lots of hydroxide ions (OH⁻).
Characteristics of Strong Alkalis: Since strong alkalis produce many hydroxide ions (OH⁻), their solutions have a very high pH. A high pH means the solution is very basic, or very alkaline, and can feel very slippery.
Examples of Strong Alkalis: Some strong alkalis are sodium hydroxide (NaOH), potassium hydroxide (KOH), and barium hydroxide (Ba(OH)₂). These substances break down fully into ions when put into water.
Weak Alkalis
Definition of Weak Alkalis: Weak alkalis are substances that do not completely break apart into ions when they dissolve in water. Only some of their molecules turn into hydroxide ions (OH⁻).
Characteristics of Weak Alkalis: Because weak alkalis produce fewer hydroxide ions (OH⁻) compared to strong alkalis, their solutions are less basic. Their pH values are lower than those of strong alkalis.
Examples of Weak Alkalis: A good example of a weak alkali is aqueous ammonia (NH₃). When ammonia dissolves in water, it creates a balance between ammonium ions (NH₄⁺) and hydroxide ions (OH⁻), with many ammonia molecules remaining unbroken.