Concentrated and dilute acids and bases

1. Definition of Concentration

• The concentration of an acid or base refers to the number of moles of solute per unit volume of solution.
• Both strong and weak acids/bases can be concentrated or dilute.

2. Key Differences

Type	Definition	Examples
Concentrated Solution	High number of moles of acid/base per unit volume	$1$ $mol·dm⁻³ HCl$ (strong acid), $1$ $mol·dm⁻³ CH₃COOH$ (weak acid), 1 $$mol·dm⁻³ NaOH (strong base)
Dilute Solution	Low number of moles of acid/base per unit volume	$0.01$ $mol·dm⁻³ HCl,$ $0.01$ $mol·dm⁻³ NH₃$ (weak base)

3. Strong vs. Weak Acids and Bases

• Strong acids and bases ionise completely in water.
• Weak acids and bases ionise partially in water.
• Concentration and strength are different concepts!
  • Example: A concentrated weak acid (e.g., $1$ $mol·dm⁻³ CH₃COOH)$ still ionises partially, while a dilute strong acid (e.g., $0.01$ $mol·dm⁻³ HCl$) ionises completely.

4. Effect of Concentration on pH

• pH is affected by concentration:
  • Higher $[H_3O^+]$ → Lower $pH$ (More acidic).
  • Higher $[OH^-]$ → Higher $pH$ (More basic).
• pH Ranges:
  • Strong acid: $pH$ $1 – 2$ (concentrated), $pH$ $3 – 6$ (dilute).
  • Strong base: $pH$ 12 – 14 (concentrated), $pH$ $8 – 11$ (dilute).

5. Electrical Conductivity & Reaction Rate

• Higher concentration = More ions = Greater conductivity.
• Higher concentration = Faster reaction rate.
  • Example: $1$ $mol·dm⁻³ HCl$ reacts faster with a metal than $0.01$ $mol·dm⁻³ HCl.$

6. Key Takeaways

• Concentration refers to the number of moles per volume.
• Strength refers to the extent of ionisation in water.
• Both strong and weak acids/bases can be concentrated or dilute.
• Higher concentration increases conductivity and reaction rate.