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Chapter 10: Problem 12

Rationalize why chalk (calcium carbonate) has a higher melting point than motor oil (large compound made from carbon and hydrogen), which has a higher melting point than water and engages in relatively strong hydrogen bonding interactions.

Short Answer

Expert verified
Chalk (calcium carbonate) has a higher melting point than motor oil and water due to its strong ionic bonding, which requires more energy to break compared to the covalent and London dispersion forces in motor oil. While hydrogen bonding in water is stronger than London dispersion forces in motor oil, it is weaker than the ionic bonding in chalk. This results in an order of melting points: chalk > motor oil > water, which correlates with the strength of their bonding and intermolecular forces.

Step by step solution

01

Identify the types of bonding and intermolecular forces in each substance

For chalk (calcium carbonate, CaCO3), the primary bonding is ionic bonding between calcium ions (Ca2+) and carbonate ions (CO3²-). For motor oil, the primary bonding is covalent bonding (strong) between carbon and hydrogen atoms. Due to the presence of large carbon and hydrogen chains, motor oil molecules also have weak London dispersion forces. For water (H2O), the intermolecular force is hydrogen bonding which is a strong type of dipole-dipole interaction.
02

Compare the strength of the ionic bonding in chalk to the covalent and London dispersion forces in motor oil

The ionic bonding in chalk (CaCO3) is much stronger than the covalent and London dispersion forces in motor oil. This is due to the electrostatic attraction between the oppositely charged ions (Ca2+ and CO3²-) in chalk, which results in a crystalline lattice structure. The covalent bonds within motor oil are relatively strong, but the overall London dispersion forces between the molecules are weaker compared to the ionic bonding in chalk. This means that more energy is required to break the ionic bonds in chalk, resulting in a higher melting point.
03

Compare the strength of the hydrogen bonding in water to the covalent and London dispersion forces in motor oil

Hydrogen bonding in water is a strong type of dipole-dipole interaction due to the electronegativity difference between oxygen and hydrogen atoms. While the strength of hydrogen bonding is more significant than London dispersion forces in motor oil, it is still weaker than the ionic bonding in chalk. Water has a lower melting point than chalk but a higher melting point than motor oil, because breaking the hydrogen bonding interactions takes less energy than breaking the ionic bonds in chalk, but more energy than overcoming the London dispersion forces in motor oil.
04

Rationalize the order of melting points

Chalk (calcium carbonate) has a higher melting point than motor oil due to its strong ionic bonding, which requires much more energy to break compared to the covalent and London dispersion forces in motor oil. Motor oil has a higher melting point than water because, while the hydrogen bonding in water is strong, it is weaker than the covalent bonds found in motor oil. Therefore, the order of melting points is chalk > motor oil > water, which correlates with the strength of their bonding and intermolecular forces.

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Most popular questions from this chapter

Consider the following enthalpy changes: $$ \begin{aligned} \mathrm{F}^{-}+\mathrm{HF} \longrightarrow \mathrm{FHF}^{-} \quad \Delta H=-155 \mathrm{~kJ} / \mathrm{mol} \\ \left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}+\mathrm{HF} \longrightarrow\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}-\mathrm{-HF} \\ \Delta H=-46 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{HOH}(g) \longrightarrow \mathrm{H}_{2} \mathrm{O}--\mathrm{HOH}(\text { in ice }) \\ \Delta H=-21 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$ How do the strengths of hydrogen bonds vary with the electronegativity of the element to which hydrogen is bonded? Where in the preceding series would you expect hydrogen bonds of the following type to fall?

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Rationalize the differences in physical properties in terms of intermolecular forces for the following organic compounds. Compare the first three substances with each other, compare the last three with each other, and then compare all six. Can you account for any anomalies? $$ \begin{array}{|lccc|} \hline & \text { bp }\left({ }^{\circ} \mathrm{C}\right) & \operatorname{mp}\left({ }^{\circ} \mathrm{C}\right) & \Delta H_{\text {vap }}(\mathbf{k J} / \text { mol }) \\ \hline \text { Benzene, } \mathrm{C}_{6} \mathrm{H}_{6} & 80 & 6 & 33.9 \\ \text { Naphthalene, } & & & \\ \mathrm{C}_{10} \mathrm{H}_{8} & 218 & 80 & 51.5 \\ \text { Carbon tetra- } & & & \\ \text { chloride } & 76 & -23 & 31.8 \\ \text { Acetone, } & & & \\ \mathrm{CH}_{3} \mathrm{COCH}_{3} & 56 & -95 & 31.8 \\ \text { Acetic acid, } & & & \\ \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H} & 118 & 17 & 39.7 \\ \text { Benzoic acid, } & & & \\ \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO}_{2} \mathrm{H} & 249 & 122 & 68.2 \\\ \hline \end{array} $$
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