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This question is about structure and bonding - AQA - A-Level Chemistry - Question 8 - 2019 - Paper 1
Question 8
This question is about structure and bonding. 1. Draw a diagram to show the strongest type of interaction between two molecules of ethanol (C2H5OH) in the liquid ph... show full transcript
Worked Solution & Example Answer:This question is about structure and bonding - AQA - A-Level Chemistry - Question 8 - 2019 - Paper 1
Step 1
Draw a diagram to show the strongest type of interaction between two molecules of ethanol in the liquid phase.
Answer
To represent the strongest type of interaction between two ethanol molecules, we need to draw hydrogen bonding. In each ethanol molecule (C2H5OH), the oxygen atom has two lone pairs of electrons and is partially negative, while the hydrogen atom bonded to oxygen is partially positive. The following diagram illustrates this:
H H
| |
H-C---C
| |
O---H
||
:O:
H-bonding
This diagram shows two ethanol molecules interacting through hydrogen bonds.
Step 2
In terms of the intermolecular forces involved, explain the difference in boiling points.
Answer
Ethanol has a boiling point of 78 °C, while methoxymethane has a much lower boiling point of -24 °C. This significant difference can be attributed to the types of intermolecular forces at play. Ethanol molecules are capable of forming hydrogen bonds due to the presence of an -OH group, which leads to stronger interactions between molecules. In contrast, methoxymethane primarily experiences weaker van der Waals forces, making them less effective in keeping the molecules together at room temperature. Consequently, the energy required to break these weaker interactions in methoxymethane is much lower, resulting in a lower boiling point compared to ethanol.
Step 3
Draw the shape of the POCl3 molecule and the shape of the ClF3⁻ ion. Include any lone pairs of electrons that influence the shapes.
Answer
For the POCl3 molecule, the shape is based on a tetrahedral geometry because the phosphorus atom is bonded to three chlorine atoms and one oxygen atom. The lone pair from oxygen does not significantly influence the molecular shape.
The structure can be represented as:
Cl
|
P----O
/ \
Cl Cl
For the ClF3⁻ ion, which has a distorted tetrahedral shape due to the presence of two lone pairs of electrons, it can be depicted as:
F
|
F-Cl
|
:O:
The suggested bond angle in ClF3⁻ is approximately 90° due to the repulsion caused by the lone pairs.