Acids and Bases

Acids:

• - Is a substance that donates a proton (H+ ions)
• - In aqueous solutions, these H+ ions combine with H2O molecules to form hydronium ions H3O+ (aq), which are also written as H+.
• - The H3O+ ions make the solution acidic.

EXAMPLE:

• When HCl gas dissolves in water, HCl acts as an acid by donating protons (H+ ions) to water molecules.
• The water acts as a base
• The H+ and Cl- dissociate/ split up
• 
• Caption: Just notice how H20 is the proton acceptor and HCl is the proton donor. Also that the hydronium ion and Cl- is formed.

Some are strong and some are weak...

• Strong acids:
• eg: HCl, NHO3 and H2SO4
• - Completely dissociate into ions in aqueous solution
• - A strong acids reaction with water goes to completion. Meaning all acid molecules are "split up" as they react with water, donating H+ to H2O in order to form H3O+
• eg:
• HCl + H2O --> Cl- + H3O+
• HNO3 + H2O --> NO3- + H30+
• Weak acids:
• eg: CH3COOH, HF, NH4+
• - Weak acids only partially dissociate into ions in aqueous solution.
• - A weak acids reaction with water is incomplete - most acid particles remain "whole" with only a small number reacting with water to form the hydronium ion.
• These reactions are equilibrium reactions that favour reactants. (Small numbers of acid particle dissociate before equilibrium is reached.

Properties of Strong & Weak Acids.

• STRONG ACIDS:
• Because ions completely dissociate in aqueous solution, there is a higher concentration of ions....
• - A high concentration of ions means a high electrical conductivity
• - A high concentration of hydronium ions means a low pH (e.g. pH of 1)
• - A high concentration of hydronium ions means a fast rate of reaction.
• WEAK ACIDS:
• Because weak acids on partially dissociate into ionise aqueous solution...
• - A low concentration of ions means a low electrical conductivity
• - A low concentration of the hyrdonium ions means a higher pH (e.g.: 4)
• - A low concentration of the hydronium ions means a slow rate of reaction.

Dilute and concentrated acids.

• "Weak" and "Strong" acids refer to the amount of acid dissociations whereas "dilute" and "concentrated" refer to the number of acid particles (mol/L)

Dilute and Concentrated acids:

• Dilute:
• -Diluting an acid results in less hydronium ions per unit of volume, so the pH increases
• eg: a 0.1 mol/L HCl solution has [Hydronium ion] of 0.1 mol/L resulting in a pH of 1
• a 0.01 mol/L HCl solution has [Hydronium ion] of 0.01 mol/L resulting in a pH of 2
• - A dilute strong acid (meaning the ions have completely dissociated), is still a strong acid. Diluting any acid just simply reduces the concentration of hydronium ions (acidity/pH)
• Concentrated:
• - Concentrating an acid results in more hyrdonium ions per volume, so the pH decreases.
• - A concentrated weak acid (meaning ions have partially dissociated) is still a weak acid. Concentrating any acid just simply increases the concentration of hydronium ions (acidity/pH)

Acids with metals- rates of reaction...

• A concentrate acid reacts more rapidly as it has a higher concentration of hydronium ions.
• A strong acid reacts more rapidly as it has a higher concentration of hydronium ions.

Bases:

• - A base is a substance that accepts protons (H+)
• - In an aqueous solution, molecular bases accept H+ ions donated by H2O molecules, converting them into hydroxide ions OH- (aq).
• - The OH- ions make the solution alkaline.