This option builds on some of the key ideas in both physical and organic chemistry that were introduced in the core.
A.1 Determination of Structure (5h)
A.1.1 State that the structure of a compound can be
determined by using information from a variety of spectroscopic and
Students should realise that information from only one technique is usually insufficient to determine or confirm a
A.1.2 Describe and explain how information from an
infrared spectrum can be used to identify functional groups in a
Restrict this to using infrared spectra to show the presence of the functional groups :
A.1.3 Describe and explain how information from a
mass spectrum can be used to determine the structure of a compound.
Restrict this to using mass spectra to determine the relative molecular mass of a compound and to identify simple
fragments, for example :
A.1.5 Describe and explain the structure of benzene
using chemical and physical evidence.
Consider the special stability of the ring system (heat of combustion or hydrogenation of C6H6 in comparison to
that of cyclohexene, cyclohexadiene and cyclohexatriene), as well as benzene's tendency to undergo substitution
rather than addition reactions.
A.2 Rate Expression (3h)
A.2.1 Define the terms rate constant and order of reaction.
A.2.2 Derive the rate expression for a reaction from
Rate = k[A]m[B]n
where k = rate constant, [A] = concentration of A in mol dm-3 etc.
m and n = integers, m + n = overall order of the reaction.
A.2.3 Draw and analyse graphical representations for zero-, first- and second- order reactions.
A.2.4 Define the term half-life and calculate
the half-life for first-order reactions only.
The half-life should be calculated from graphs and by using the integrated form of the rate equation. The
integrated rate equation for second-order reactions is not required.
A.3 Reaction Mechanism (1h)
A.3.1 Define the terms rate-determining step, molecularity and activated complex.
A.3.2 Describe the relationship between mechanism,
order, rate-determining step and activated complex.
Limit examples to one- or two-step reactions where the mechanism is known. Students should understand what
an activated complex (transition state) is and how the order of a reaction relates to the mechanism.
A.4 Nucleophilic Substitution Reactions (5h)
A.4.1 Distinguish between primary, secondary and tertiary halogenoalkanes.
A.4.2 Describe and explain the SN1 and
SN2 mechanisms in nucleophilic substitution.
Students must be able to draw a stepwise mechanism. Examples of nucleophiles should include -CN, -OH and
NH3 for each reaction type.
A.4.3 Describe and explain the molecularity for the
SN1 and SN2 mechanisms.
The predominant mechanism for tertiary halogenoalkanes is SN1 and for primary halogenoalkanes it is SN2. Both
mechanisms occur for secondary halogenoalkanes.
A.4.4 Describe how the rate of nucleophilic substitution
in halogenoalkanes depends on both the identity of the halogen and
whether the halogenoalkane is primary, secondary or tertiary.
A.5 Acids, Bases and Buffers (4h)
A.5.1 State the expression for the ionic product
constant of water (Kw).
Kw = [H+ (aq)][OH-(aq)] = 1.0 x 1.0-14 mol2 dm-6 at 298 K, but this varies with temperature.
A.5.2 Deduce [H+(aq)] and [OH-(aq)] for water at different temperatures given Kw values.
A.5.3 Define pH, pOH and pKw.
A.5.4 Calculate [H+(aq)], [OH-(aq)],
pH and pOH from specified concentrations.
The values of [H+(aq)] or [OH-(aq)] are directly related to the concentration of the acid or base.
A.5.5 State the equation for the reaction of any
weak acid or weak base with water and hence derive the ionization constant
In general HA(aq) === H+(aq) + A-(aq)
B(aq) + H2O(l) === BH+(aq) + OH-(aq) (base hydrolysis)
Then Ka = and Kb
Examples used should involve the transfer of only one proton.
A.5.6 State and explain the relationship between Ka and pKa.
A.5.7 Determine the relative strengths of acids or their conjugate bases from Ka or pKa values.
A.5.8 Apply Ka or pKa in calculations.
Calculations can be performed using various forms of the acid ionization constant expression (see A.5.5).
Students should state when approximations are used in equilibrium calculations. Use of the quadratic expression is
A.5.9 Calculate the pH of a specified buffer system.
Calculations will involve the transfer of only one proton. Cross reference with 9.4.
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