A solution forms when a solute dissolves in a solvent. The concentration of a solution is a measure of how ‘crowded’ the solute particles are. The more concentrated the solution, the more solute particles it contains in a given volume.
Solutions are described as dilute or concentrated, depending on the ratio of dissolved solute to volume of solution:
Take care to use the word ‘dilute’ correctly. It can be used to describe the concentration of a solution (as here), or to describe the process of adding more water to a solution to reduce its concentration.
Strong acids completely dissociate in solution. For example, hydrochloric acid is a strong acid. It completely dissociates to form hydrogen ions and chloride ions:
HCl(aq) → H+(aq) + Cl-(aq)
Nitric acid and sulfuric acid are also strong acids.
Weak acids only partially dissociate in solution. For example, ethanoic acid is a weak acid. It only partially dissociates to form hydrogen ions and ethanoate ions:
CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)
The ⇌ symbol is used in the equation to show that the reaction is a reversible reaction, and does not go to completion.
The pH of a solution is a measure of its concentration of hydrogen ions. The higher the concentration of H+ ions in an acidic solution, the lower the pH.
If the hydrogen ion concentration in a solution increases by a factor of 10, the pH of the solution decreases by 1.
pH of alkaline solution
The higher the concentration of OH- ions in an alkaline solution, the higher the pH.