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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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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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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d)
Formulate two equations to show how nitrogen(II) oxide, NO, catalyses the destruction of ozone.
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a)
Cyclohexane C6 H12 has a puckered, non-planar shape whereas benzene C6 H6 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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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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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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d)
A molecule of ethanol is shown below.
Deduce the hybridisation of the carbon atom marked in the diagram below.
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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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b)
Explain, with the use of diagrams, how there are three valid structures for the carbonate ion.
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c)
Describe the distribution of pi (π) electrons and explain how this can account for the structure and stability of the carbonate ion, CO3 2– .
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d)
Identify and explain the bond order of the carbonate ion.
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a)
Explain how the concept of hybridisation can be used to explain the triple bond present in propyne.
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b)
Consider the molecule below which contains both sigma and pi bonds.
How many carbon atoms exhibit sp2 hybridisation in this molecule.
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c)
The concentration of ozone in the upper atmosphere is maintained by the following three reactions, I , II and III
Explain which reaction requires the most energy
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d)
Deduce the hybridisation shown by the nitrogen atoms in NF4 + , N2 H2 and N2 H4 .
NF4 + N2 H2 N2 H4
Hybridisation
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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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b)
Explain why ozone can be dissociated by light with a longer wavelength than required to decompose oxygen.
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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, H2 O2 , and in the oxygen molecule, O2
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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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