IB Chemistry SL 3.2.4 Physical Property Trends Questions

Use real exam questions to rank melting and boiling points and explain trends using chain length, branching, polarity, packing and intermolecular forces.

Exam points

Rank or compare boiling points using chain length, relative molecular mass, branching and the strength of London dispersion forces.
Rank or compare melting points using saturation/unsaturation, cis/trans shape, chain length and how closely molecules pack.
Explain physical-property differences between organic compounds using polarity, hydrogen bonding and other intermolecular forces.

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Study 3.2.4—Physical property trends conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[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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IB Chemistry SL 3.2.4 Physical Property Trends Questions question 1