IB Chemistry SL 3.2.4 Physical property trends Question Bank

Practise IB Chemistry SL 3.2.4 by relating organic structure and intermolecular forces to boiling point, melting point and physical behaviour.

Exam points

Explain how chain length, branching or functional group changes a boiling or melting point.
Use intermolecular forces to compare physical properties of organic compounds.
Distinguish fractional distillation from cracking and link each process to a physical trend.

[Maximum number: 2]

$\quad \mathrm{C}_{5} \mathrm{H}_{12}$ exists as three isomers. Identify the structure of the isomer with the lowest boiling point and explain your choice.

$\quad \mathrm{C}\left(\mathrm{CH}_{3}\right)_{4}$ ;

Marking guidance:

Accept correct name 2,2-dimethylpropane.
Do not penalize missing H atoms.
weakest London/dispersion/van der Waals'/vdW/instantaneous induced dipoleinduced dipole forces because of smallest surface area/contact
OR
weakest London/dispersion/van der Waals'/vdW/ instantaneous induced dipoleinduced dipole forces because of least distortion of the electron cloud OR
weakest London/dispersion/van der Waals'/vdW/ instantaneous induced dipoleinduced dipole forces because polarizability of electrons (in electron cloud) is less;

Accept other words to that effect but student must mention a correct IMF and a correct reason.

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3.2.4—Physical property trends question 1