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In this unit, students learn about the differences between strong and weak acids and bases. Material covered includes Theories of acids and bases, properties of acids and bases, the pH scale. HL students will also study calculations involving acids and bases , buffer solutions, salt hydrolysis, acid base titrations and indicators.

Essential idea

Many reactions are reversible. These reactions will reach a state of equilibrium when the rates of the forward and reverse reaction are equal. The position of equilibrium can be controlled by changing the conditions.

Learning Targets


Moral Citizens - My pollution, your problem?

Topics 8(SL) & 18(HL) Acids and Bases

8.1 Theories of acids and bases

  • Define acids and bases according to the Brønsted–Lowry theory
  • Deduce whether or not a species could act as a Brønsted–Lowry acid or base.
  • Deduce the formula of the conjugate acid (or base) of any Brønsted–Lowry base (or acid).

8.2 Properties of acids and bases

  • Outline the characteristic properties of acids and bases in aqueous solution
  • Identify the acid and base needed to prepare a given salt
  • Experience of titrations with different indicators.

8.3 The pH scale

  • Understanding of the pH scale
  • Problem solving involving pH, [H+] , [OH-] and Kw (the ionic product of water)

8.4 Strong and weak acids and bases

  • Distinguish between strong and weak acids and bases in terms of the extent of dissociation, reaction with water and electrical conductivity
  • State whether a given acid or base is strong or weak
  • Distinguish between strong and weak acids and bases, and determine the relative strengths of acids and bases using experimental data

8.5 Acid Deposition

  • An understanding of the term acid rain and explain why rainwater is naturally acidic
  • An understanding of the process of acid deposition
  • Describe the sources of acid deposition and the effect on the environment
  • Write balanced chemical equations for acid deposition and reactions in the environment
  • Distinguish between re-combustion and post-combustion methods of reducing sulphur oxide emissions

Topic 18: Acids and Bases (HL Students only)


Moral Citizens - Primary pollutants result in acid deposition (secondary pollutants) in regions far from the primary source. Solving this problem requires international cooperation.

18.1 Calculations involving acids and bases

  • State the expression for the ionic product constant of water (Kw)
  • educe [H+(aq)] and [OH-(aq)] for water at different temperatures given Kw values
  • Solve problems involving [H+(aq)], [OH-(aq)], pH and pOH
  • State the equation for the reaction of any weak acid or weak base with water, and hence deduce the expressions for Ka and Kb
  • Solve problems involving solutions of weak acids and bases using the expressions: Ka × Kb = Kw
  • pKa + pKb = pKw
  • pH + pOH = pKw
  • Identify the relative strengths of acids and bases using values of Ka, Kb, pKa and pKb

18.2 Buffer solutions

  • Describe the composition of a buffer solution and explain its action
  • Solve problems involving the composition and pH of a specified buffer system

18.3 Salt hydrolysis

  • Deduce whether salts form acidic, alkaline or neutral aqueous solutions

18.4 Acid–base titrations

  • Sketch the general shapes of graphs of pH against volume for titrations involving strong and weak acids and bases and explain their important features

18.5 Indicators

  • Describe qualitatively the action of an acid–base indicator
  • State and explain how the pH range of an acid–base indicator relates to its pKa value
  • Identify an appropriate indicator for a titration, given the equivalence point of the titration and the pH range of the indicator

The detailed curriculum can be consulted here.

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