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A LevelChemistryCIEExam Questions3. Chemical Bonding3.6 Intermolecular Forces, Electronegativity & Bond Properties

Intermolecular Forces, Electronegativity & Bond Properties (CIE A Level Chemistry)

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3.6 Intermolecular Forces, Electronegativity & Bond Properties

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3.6 Intermolecular Forces, Electronegativity & Bond Properties

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1a2 marks

There are a number of different types of intermolecular forces possible between molecules.

Name the three main types and place them in ascending order of strength.

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1b2 marks

Methanol (CH3OH) is a small alcohol molecule with many uses. 


Draw a diagram to show how two methanol molecules interact with each other through hydrogen bonding in the liquid phase.

Include all partial charges and all lone pairs of electrons in your diagram.

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1c4 marks

Methanol, CH3OH can be oxidised to methanal, CH2O and then to methanoic acid, HCOOH.

Identify the strongest type of intermolecular force between:

i)
Methanal molecules
[1] 
ii)
Methanoic acid molecules
[1] 
iii)
Water and methanal
[1] 
iv)
Water and methanoic acid
[1]

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1d3 marks

Methanoic acid reacts with sodium hydroxide to form sodium methanoate:

HCOOH + NaOH rightwards arrowHCOONa + H2O

Explain why sodium methanoate is a solid at room temperature and methanoic acid is a liquid.

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1e2 marks
Complete the dot-and-cross diagram of methanol, CH3OH.

2-4_q4c-ocr-a-as--a-level-easy-sq

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1a3 marks

Ammonia, NH3, and methane, CH4, are the hydrides of elements which are next to one another in the Periodic Table.

In the boxes below, draw the ‘dot-and-cross’ diagram of a molecule of each of these compounds.

Show outer electrons only.

State the shape of each molecule.

NH3

 

 

 

 

CH4

 

 

 

 

shape

  

shape 

  

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1b3 marks

Ammonia is polar whereas methane is non-polar. The physical properties of the two compounds are different.

i)
Explain, using ammonia as the example, the meaning of the term bond polarity.

[2]

ii)
Explain why the ammonia molecule is polar.
[1]

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1c1 mark

State one physical property of ammonia which is caused by its polarity.

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1d3 marks

When ammonia gas is mixed with hydrogen chloride, white, solid ammonium chloride is formed.

State each type of bond that is present in one formula unit of ammonium chloride and how many of each type are present.

You may draw diagrams.

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2a2 marks

The structural formulae of water, methanol and methoxymethane, CH3OCH3, are given below. 

1-3-chemical-bonding-2a

i)
How many lone pairs of electrons are there around the oxygen atom in methoxymethane?
[1]

ii)
Suggest the size of the C–O–C bond angle in methoxymethane.
[1]

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2b4 marks

The physical properties of a covalent compound, such as its melting point, boiling point, vapour pressure, or solubility, are related to the strength of attractive forces between the molecules of that compound.

These relatively weak attractive forces are called intermolecular forces. They differ in their strength and include the following.

 A  interactions involving permanent dipoles
 B  interactions involving instantaneous dipole-induced dipoles
 C  hydrogen bonds

By using the letters A, B, or C, state the strongest intermolecular force present in each of the following compounds.

For each compound, write the answer on the dotted line:

 ethanal  CH3CHO ...................
 ethanol  CH3CH2OH ...................
 methoxymethane  CH3OCH3 ...................
 2-methylpropane  (CH3)2CHCH3 ...................

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2c4 marks

Methanol and water are completely soluble in each other.

i)
Which intermolecular force exists between methanol molecules and water molecules that makes these two liquids soluble in each other?
[1]

ii)
Draw a diagram that clearly shows this intermolecular force. Your diagram should show any lone pairs or dipoles present on either molecule that you consider to be important.
[3]

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2d2 marks

When equal volumes of ethoxyethane, C2H5OC2H5, and water are mixed, shaken, and then allowed to stand, two layers are formed.

Suggest why ethoxyethane does not fully dissolve in water. Explain your answer.

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3a2 marks

Based on the type of intermolecular force present, explain why butan-1-ol has a higher boiling point than butanal.

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3b2 marks

Ethane, C2H6, and disilane, Si2H6, are both hydrides of Group 4 elements with similar structures but different chemical properties.

Explain why disilane has a higher boiling point than ethane.

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3c4 marks

Based on the type of intermolecular force present, explain the difference in solubility in water between ethane and ethanol.

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1a3 marks

Paperclips have a higher density than water. However, if a paperclip is lowered carefully onto the surface of water, the paperclip can float. When a drop of liquid soap is added to the water, the paperclip sinks.

Suggest explanations for these observations.

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1b4 marks

Ammonia is highly soluble in water. Draw diagrams to show the two ways that intermolecular forces can form between a molecule of water and a molecule of ammonia to explain this.

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1c5 marks

NH3, HCl and F2 all exist as gases at room temperature and pressure.

NH3 has the highest boiling point of -33 °C .


Predict whether HCl or F2 has the lowest boiling point and explain why there is a difference between their boiling points.

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