Question

rank the elements or compounds in the table below in decreasing order of their boiling points. that is, choose 1 next to the substance with the highest boiling point, choose 2 next to the substance with the next highest boiling point, and so on.
substance | chemical symbol, chemical formula or lewis structure | boiling point
a |

h h
| |
h—c—c—o—h
| |
h h

| select
b | cao | select
c | co | select
d |

h h
| |
h—c—o—c—h
| |
h h

| select

Explanation:

Step1: Identify Bond Types and Forces

• Substance A: Lewis structure shows an alcohol (has -OH group), so it can form hydrogen bonds. Also has London dispersion forces (LDF) and dipole - dipole interactions.
• Substance B: \(CaO\) is an ionic compound. Ionic compounds have strong ionic bonds, which are electrostatic attractions between cations and anions.
• Substance C: \(CO\) is a covalent compound. It has dipole - dipole interactions (since it's a polar molecule, \(C\) and \(O\) have different electronegativities) and LDF.
• Substance D: Lewis structure shows an ether? Wait, no, looking at the structure, it's a molecule with \(C - O - C\) and \(C - H\) bonds. It has dipole - dipole interactions (due to the polar \(C - O\) bonds) and LDF. But no hydrogen bonding (since the \(O\) is not bonded to an \(H\) that can participate in H - bonding like in - OH or - NH groups).

Step2: Compare Strength of Intermolecular Forces

• Ionic bonds (in \(CaO\)) are much stronger than hydrogen bonds, dipole - dipole, and LDF. So \(CaO\) (substance B) has the highest boiling point because more energy is required to break ionic bonds.
• Next, substance A (alcohol) can form hydrogen bonds. Hydrogen bonds are stronger than dipole - dipole and LDF. So among the remaining, A has stronger intermolecular forces than C and D.
• Substance D: Let's analyze its molar mass. The formula for D: looking at the Lewis structure, it's \(C_2H_5 - O - C_2H_5\) (diethyl ether? Wait, no, the structure given: \(H - C - H\) (four H around the first C), then \(C - O - C\), then the other C has four H. So molecular formula is \(C_2H_5OC_2H_5\) or \(C_4H_{10}O\). Molar mass: \(4\times12 + 10\times1+16=48 + 10+16 = 74\) g/mol.
• Substance A: The Lewis structure is \(CH_3CH_2OH\) (ethanol), molar mass \(2\times12 + 6\times1+16 = 46\) g/mol. Wait, but hydrogen bonding in A is stronger. Wait, no, maybe I made a mistake. Wait, the structure of A: two C atoms, one with three H, one with two H and an - OH. So \(C_2H_5OH\) (ethanol, molar mass 46 g/mol). Structure of D: \(C_2H_5OC_2H_5\) (diethyl ether, molar mass 74 g/mol). Even though D has a higher molar mass (so stronger LDF), A has hydrogen bonding. The strength of hydrogen bonding is generally stronger than the increase in LDF from molar mass difference here? Wait, no, actually, diethyl ether (D) does not have hydrogen bonding, while ethanol (A) does. But wait, the boiling point of ethanol is about 78°C, diethyl ether is about 35°C. So A has a higher boiling point than D. Then \(CO\) (substance C) has a molar mass of \(12 + 16=28\) g/mol, and it's a polar molecule but with relatively weak dipole - dipole forces compared to A and D.

So the order of boiling points from highest to lowest: \(B (CaO)>A (C_2H_5OH)>D (C_4H_{10}O)>C (CO)\)

Answer:

1. Highest boiling point: B (CaO)
2. Next highest: A (\(CH_3CH_2OH\) or the Lewis structure shown for A)
3. Next: D (the Lewis structure shown for D)
4. Lowest: C (CO)