Acids And Bases Ionization

What is Ionization?

Ionization of a compound is the splitting of a neutral molecule into charged ions when it comes into contact with a solution. When a compound is dissolved in a solvent, it breaks apart into positive and negative ions called electrolytes. The degree of ionization is the ratio of the number of molecules that are breaking apart to the total number of molecules.

𝞪 = number of molecules undergoing dissociation/ total number of molecules

Where 𝞪 is called the degree of ionization

Arrhenius’s concept of Acid and base ionization

Arrhenius’s theory says that acids are compounds that break apart in water to release hydrogen ions (H+) (aq). On the other hand, bases are substances that give off hydroxyl ions (OH–(aq)) in water.

Since most ionization happens in water, Arrhenius’s theory is a key part of explaining how acids and bases become charged. We can figure out how strong acids and bases are by looking at how much ionization they have. Different acidic and basic compounds have different amounts of ionization. Some acids, like perchloric acid (HClO4) and hydrochloric acid (HCl), completely break apart into their individual ions in water. The name for these acids is “strong acids.”

When acids are ionized, they give off hydrogen ions. This means that acids are proton donors. In the same way, some bases, such as lithium hydroxide (LiOH) and sodium hydroxide (NaOH), completely separate into their ions in water. We call these “strong bases.” When these bases are broken down, they give off hydroxyl ions (OH–).

So, the amount of ionization of acids and bases depends on how much compounds break apart into their individual ions. When compared to weak acids and bases, strong acids and bases have a lot of ions. A strong acid also means that it is a good proton donor, while a strong base means that it is a good proton acceptor. For example, the weak acid HA can split apart.

Explanation of Arrhenius acid and base ionization

This reaction shows that the acid dissociation equilibrium is dynamic and that proton transfer can happen both forward and backward. If HA is more likely than H₃O+ to give up a proton, then HA acts as a strong acid compared to H₃O+. Since the acid that is stronger gives a proton to the base that is stronger. The equilibrium moves in the direction of making an acid and a base that are both weaker. Most of the time, the conjugate bases of strong acids are weaker than the conjugate acids of strong bases. This is because strong acids and bases have a lot of ions in them.

Determination of ionization constant of acid and base

Based on what we’ve talked about so far, we can say that when an Arrhenius acid splits, it does so in the following way.

HA (aq) + H₂O (l) ⇌ H₃O⁺(aq) + A⁻(aq)

So according to the equilibrium constant;

K=[H3⁢O+]⁢[A−][H⁢A]⁢[H2⁢O]

K [H₂O] = [H₃O⁺] [A⁻] / [HA]

K_a = [H₃O⁺] [A⁻] / [HA]

Where K_a is known as the ionization constant of acid, for stronger acid K_a value will be higher.

Similarly for Arrhenius’s base

BOH (aq) + H₂O (l) ⇌ B⁺ (aq) + OH⁻(aq)

So according to the equilibrium constant;

K=[B+]⁢[O⁢H−][B⁢O⁢H]⁢[H2⁢O]

K [H₂O] = [B⁺] [OH⁻] / [BOH]

K_b = [B⁺] [OH⁻] / [BOH]

Where K_b is known as the ionization constant of the base, for a stronger base, the K_b value will be higher.

Examples of Acid and Base ionization

The equation for the ionization of CH₃COOH and NH₄OH.

Ionization of acetic acid in aqueous solution: CH₃COOH + H₂O  ⇋  H₃O⁺ + CH₃COO^–

Ionization of ammonium hydroxide in aqueous solution; NH₄OH + H₂O  ⇋  NH₄⁺ + OH^–

Frequently Asked Questions – FAQs

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