DP IB Chemistry: HL

Topic Questions

IBChemistry: HLDPTopic Questions14. Chemical Bonding & Structure (HL only)14.2 Further Aspects of Bonding

Syllabus Edition

First teaching 2014

Last exams 2024

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14.2 Further Aspects of Bonding

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1a1 mark

State what is meant by the term delocalisation of electrons.

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1b3 marks

Delocalisation is common in some types of organic molecule.
 

i)
Identify whether ethanoic acid, CH3COOH, has delocalised straight pi electrons.

[1]

ii)
Identify where the ethanoate ion, CH3COO-, has delocalised electrons.

[1]

iii)
Give a reason for your choices.

[1]

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1c2 marks

Draw two resonance structures for the ethanoate ion, CH3COO-.

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1d1 mark

Deduce the bond order of the C-O bonds in the ethanoate ion.

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2a1 mark

Benzene, C6H6, has two resonance structures. Draw skeletal formulae of these two structures.

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2b2 marks

Benzene is commonly drawn in the following manner:

benzene-ib-hl-sq-14-2-2b

Explain what this represents and why this is a useful way to draw benzene.

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2c2 marks

Some of the sigma bonds in benzene are formed from hybrid orbitals. The type of hybridisation present is sp2.

State which orbitals hybridise to form sp2 orbitals.

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2d2 marks

The sp2 hybridized orbitals form sigma bonds in the benzene molecule. The delocalised electrons from pi bonds.
 

i)
Deduce the number of sigma (straight sigma) bonds in benzene.
[1]
ii)
Deduce the number of pi (straight pi) bonds in benzene.
[1]

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3a2 marks

Ozone, O3, forms two resonance structures, shown below:

ozone-resonance-structuresib-hl-sq-14-2-q3a 
i)
Allocate formal charges to the oxygen atoms in the left-hand diagram.
[1]
ii)
Deduce the bond order for the O-O bond in ozone.

[1]

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3b2 marks

The bond order of oxygen, O2, molecules is 2.

 
i)
State which bonds are easier to break, those in oxygen or those in ozone.

[1]

ii)
Compare the wavelengths of light needed to break the bonds in oxygen and ozone respectively

[1]

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3c1 mark

Ozone, O3, can react to form oxygen, O2. Write an equation to show the overall equation for this depletion.

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3d2 marks

A number of species can catalyse the depletion of ozone, O3.

Write the molecular formulae for two catalysts of ozone depletion.

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4a3 marks

Methane contains sp3 hybridised orbitals.

i)
Explain the formation of sp3 hybridised orbitals.

[2]

ii)
How many sp3 hybridised orbitals are present in methane?

[1]

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4b4 marks

Ethyne, C2H2, is another hydrocarbon, in this case containing sp hybrid orbitals.

 
i)
Explain the formation of the sp hybrid orbitals in ethyne

[2]

ii)
Deduce the number of sp hybrid orbitals in a molecule of ethyne.
[1]
iii)
State if these sp hybrid bonds form sigma (σ) or pi (π) (bonds)

[1]

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4c2 marks

Explain, using the concept of hybridisation, how the triple bond in ethyne, C2H2, forms.

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4d2 marks

Ethanenitrile, CH3CN, is an organic molecule with a tetrahedral molecular geometry around one carbon and a linear molecular geometry around the other carbon. The structure is shown below:

ethanenitrile-ib-hl-sq-14-2-q4d

i)
Identify how many sp3 hybrid orbitals are present in this molecule.

[1]

ii)
Identify how many sp hybrid orbitals are present in this molecule.

[1]

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1a1 mark

Ibuprofen is a common non-steroidal anti-inflammatory drug (NSAID). It contains a benzene ring and a carboxylic acid at the end of one of the branches.

ibuprofen-structure-ib-hl-sq-h-14-2-q1a

Deduce the number of resonance structures possible in the deprotonated form of ibuprofen.

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1b2 marks

Deduce the number of:

 
i)
Sigma (σ) bonds in ibuprofen

[1]

ii)
Pi (π) electrons in ibuprofen

[1]

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1c2 marks

The ibuprofen molecule contains both sp3 and sp2 hybridised orbitals.

 
i)
Identify how many sp3 hybrid orbitals are present.

[1]

ii)
Identify how many sp2 hybrid orbitals are present.

[1]

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1d3 marks

Explain why the benzene ring is a regular, planar hexagon.

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2a2 marks

2-hydroxypropanenitrile, CH3CHOHCN, is a hydroxynitrile that can be formed from ethanal in a nucleophilic addition reaction.

Deduce the number of sigma (σ) and pi (π) bonds in a molecule of 2-hydroxypropanenitrile.

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2b3 marks

Deduce the number of sp3, sp2 and sp hybrid orbitals in a molecule of 2-hydroxypropanenitrile.

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2c5 marks

Describe how the concept of hybridisation can be used to explain the formation of the triple bond and C-C-N bond angle in 2-hydroxypropanenitrile.

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2d3 marks

Explain why, despite the high electron density in the triple bond, the triple bonded nitrile group is a more stable structure than the following alternative Lewis structure:

alternative-lewis-structure-for-2-hydroxypropanenitrile-ib-hl-sq-h-14-2-q2d

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3a4 marks

Predict whether ozone, O3, is a polar or non-polar molecule. Explain your choice.

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3b2 marks

Ozone can be both formed and depleted by reactions with an oxygen radical, which is an oxygen atom.

Draw a diagram to support an explanation of why an oxygen atom is a radical.

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3c3 marks

Ozone can be made and depleted in reactions involving other forms of oxygen only.

 
i)
Write one equation to show the natural formation of ozone in the atmosphere.

[1]

ii)
Write two equations to show the steps in the natural depletion of ozone in the atmosphere.

[2]

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3d6 marks

For each of the equations in part c), deduce whether the reaction is endothermic or exothermic and explain your choices.

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4a3 marks

Trichlorofluoromethane is a banned CFC, as it can lead to accelerated ozone depletion.

Write equations to show the mechanism of catalysis of ozone depletion by trichlorofluoromethane.

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4b4 marks

It is possible for the chlorine radical to undergo a termination reaction where it joins with another organic radical available, and can reform the original molecule:


Cl• (g) + CCl2F• (g) → CCl3F (g)

Explain why this is not a solution to the depletion of ozone.

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4c3 marks

CFCs have been replaced by other inert compounds, including FCs, which are fluorocarbons.

Explain why these do not pose a threat to ozone depletion.

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4d4 marks

Compounds containing iodine and carbon are usually broken down lower in the atmosphere, beneath the ozone layer. Suggest why iodocarbons are not popular alternatives to CFCs.

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1a3 marks
a)

Harmful UV radiation from the Sun is absorbed by the ozone layer. 

Explain how the bonding in O2 and O3 affects the wavelengths of UV light they absorb

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1b4 marks
b)

The chemical balance of the stratosphere is disrupted by the presence of chlorofluorocarbons (CFCs) and other ozone-depleting compounds. 

Describe, using equations, how CFCs contribute to ozone depletion using   dichlorodifluoromethane and explain the initial step by reference to the bonds in the CFC.

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1c2 marks
c)

Although the use of harmful CFCs is being phased out, suggest why these compounds are expected to remain in the atmosphere for the next 80 – 100 years.

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1d2 marks
d)

Formulate two equations to show how nitrogen(II) oxide, NO, catalyses the destruction of ozone. 

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2a4 marks
a)

Cyclohexane C6H12 has a puckered, non-planar shape whereas benzene C6H6 is planar. 

Explain this difference by making reference to the C–C–C bond angles and the type of hybridisation of carbon in each molecule.

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2b4 marks
b)

Urea, CO(NH2)2, is present in solution in animal urine. 

What is the hybridisation of C and N in the molecule, and what are the approximate bond angles?

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2c4 marks
c)
Describe the hybridisation of the carbon atom in methane and explain how the concept of hybridisation can be used to explain the shape of the methane molecule

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2d1 mark
d)

A molecule of ethanol is shown below.q2d_14-2_ib_hl_medium_sq

Deduce the hybridisation of the carbon atom marked in the diagram below.

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3a1 mark
a)
Carbonation is the process of increasing the concentration of carbonate ions in water to produce carbonated drinks. 

Identify the hybridisation of the central carbon atom.

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3b3 marks
b)

Explain, with the use of diagrams, how there are three valid structures for the carbonate ion.

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3c3 marks
c)

Describe the distribution of pi (π) electrons and explain how this can account for the structure and stability of the carbonate ion, CO32–.

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3d2 marks
d)

Identify and explain the bond order of the carbonate ion.

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4a3 marks
a)

Explain how the concept of hybridisation can be used to explain the triple bond present in propyne.

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4b1 mark
b)

Consider the molecule below which contains both sigma and pi bonds.

q4b_14-2_medium_ib_hl_sq

 How many carbon atoms exhibit sp2 hybridisation in this molecule.

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4c4 marks
c)

The concentration of ozone in the upper atmosphere is maintained by the following three reactions, I, II and III

q4c_14-2_ib_hl_medium_sq

 Explain which reaction requires the most energy

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4d3 marks
d)
Deduce the hybridisation shown by the nitrogen atoms in NF4+, N2H2 and N2H4.

   NF4+ N2H2 N2H4
Hybridisation      

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5a2 marks
a)

Sea spray is generated by the breaking of waves and releases bromine into the atmosphere. 

Write two balanced equations to show how a bromine radical could cause the destruction of ozone.

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5b3 marks
b)

Explain why ozone can be dissociated by light with a longer wavelength than required to decompose oxygen.

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5c2 marks
c)

The two oxygen-oxygen bonds in ozone are in fact of equal length. Deduce why this is the case and how the length of these would compare to oxygen-oxygen bond lengths in hydrogen peroxide,  H2O2, and in the oxygen molecule, O2

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5d3 marks
d)

One CFC, Freon-13 (chlorotrifluoromethane), which can be used as a refrigerant, has been phased out by the Montreal Protocol. 

Describe, using equations, the mechanism of the catalysis of ozone depletion by this particular CFC.

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