The Ozone Story | OCR A-Level Chemistry B (Salters) (H433)

The Ozone Story

355 questions
21 subtopics
The ten storylines, examined across all three papers
Component 01, Component 02 and Component 03

The storyline that carries intermolecular forces, kinetics and the haloalkanes: electronegativity and polarity, the Boltzmann distribution and catalysis, nucleophilic substitution, radical chain reactions, and the destruction of stratospheric ozone..

It covers electronegativity and bond polarity, intermolecular bonds, boiling points and intermolecular bonds, activation enthalpy and enthalpy profiles, collision theory and the Boltzmann distribution, following a reaction and finding the rate from a graph, catalysts and alternative reaction routes, homogeneous catalysis and intermediates, composition of gas mixtures by volume, recognising and naming haloalkanes, primary, secondary and tertiary haloalkanes, and the amines, properties and nucleophilic substitution of haloalkanes, substitution, nucleophiles and the SN2 mechanism, relative reactivity of the haloalkanes, homolytic and heterolytic fission, radicals and half curly arrows, initiation, propagation and termination in a radical chain reaction, ozone depletion by haloalkanes, ozone in the stratosphere and troposphere, radiation of the Earth and the Sun, effects of UV and visible radiation on molecules and calculations with frequency, wavelength and energy.

Sample questions from The Ozone Story

Answer each one closed book first, then open the answer.

Electronegativity and bond polarity

What does the label δ+ on an atom mean?

Show the answer
It means the atom carries a small partial positive charge because the bonding electrons have been drawn away from it.
Boiling points and intermolecular bonds

Butane and propanone both have Mr 58.0, so why does butane boil at −0.5 °C and propanone at 56 °C?

Show the answer
With the same Mr their instantaneous dipole–induced dipole bonds are similar, but propanone is polar and so has additional permanent dipole–permanent dipole attractions that need more energy to overcome.
Following a reaction and finding the rate from a graph

Why must a kinetics experiment be carried out in a thermostatted water bath?

Show the answer
Rate is extremely sensitive to temperature, so the temperature must be held constant if the effect of the variable actually being changed is to be seen.
Homogeneous catalysis and intermediates

Roughly how many ozone molecules can a single chlorine radical destroy?

Show the answer
Of the order of 10⁵ ozone molecules, before the radical is finally removed from the cycle.
Primary, secondary and tertiary haloalkanes, and the amines

Name the functional group of a primary amine and give its formula.

Show the answer
It is the amino group, –NH₂.
Substitution, nucleophiles and the SN2 mechanism

From which direction does the nucleophile approach the carbon atom?

Show the answer
From the side directly opposite the halogen, as far as possible from the electrons of the carbon–halogen bond.
Initiation, propagation and termination in a radical chain reaction

Write the two propagation steps for methane and chlorine.

Show the answer
•Cl + CH₄ → •CH₃ + HCl, then •CH₃ + Cl₂ → CH₃Cl + •Cl.
Ozone in the stratosphere and troposphere

Where does the nitrogen dioxide come from?

Show the answer
Mainly from vehicle engines and other high-temperature combustion, where nitrogen and oxygen from the air combine.

The 21 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Electronegativity and bond polarity	Recall questions on the definition and trends of electronegativity, Pauling values, and when a bond and a molecule are polar.	20
Intermolecular bonds	Recall questions on instantaneous dipole-induced dipole bonds, permanent dipole bonds and hydrogen bonding, and their relative strengths.	22
Boiling points and intermolecular bonds	Recall questions on what is broken when a molecular substance boils, the halogen boiling point trend, and why ammonia boils above phosphine.	18
Activation enthalpy and enthalpy profiles	Recall questions on the definition, symbol and units of activation enthalpy, why most collisions fail, and reading a profile.	18
Collision theory and the Boltzmann distribution	Recall questions on the two conditions for a successful collision, what the Boltzmann curve shows, and how heating changes it.	15
Following a reaction and finding the rate from a graph	Recall questions on ways of following a reaction, why a thermostatted bath is used, and finding a rate from the gradient of a curve.	9
Catalysts and alternative reaction routes	Recall questions on how a catalyst lowers the activation enthalpy, why the reactant and product levels are unchanged, and why ΔH is unaffected.	16
Homogeneous catalysis and intermediates	Recall questions on what makes catalysis homogeneous, what an intermediate is, and the two steps of the chlorine radical cycle.	18
Composition of gas mixtures by volume	Recall questions on parts per million by volume, converting between ppm and a percentage, and applying it to atmospheric gases.	18
Recognising and naming haloalkanes	Recall questions on the general formula and the halogen prefixes, naming a haloalkane, and the order in which prefixes are written.	13
Primary, secondary and tertiary haloalkanes, and the amines	Recall questions on classifying a haloalkane and an amine, and why the two classification rules are not the same.	10
Properties and nucleophilic substitution of haloalkanes	Recall questions on why ethanol is added as a solvent, the boiling point trend, and the equations for hydrolysis by hydroxide, water and ammonia.	21
Substitution, nucleophiles and the SN2 mechanism	Recall questions on what a nucleophile is, the curly arrows of the mechanism, and which bond breaks and which forms.	18
Relative reactivity of the haloalkanes	Recall questions on the carbon-halogen bond enthalpies, the silver nitrate rate experiment, and why bond strength rather than polarity decides the rate.	19
Homolytic and heterolytic fission, radicals and half curly arrows	Recall questions on the two kinds of fission and what each produces, how a radical is written, and what a half curly arrow shows.	10
Initiation, propagation and termination in a radical chain reaction	Recall questions on the three stages, why ultraviolet light is needed, and why the reaction gives a mixture of products.	14
Ozone depletion by haloalkanes	Recall questions on what a CFC is, its photodissociation, the two-step catalytic cycle, and why an HCFC was an improvement.	20
Ozone in the stratosphere and troposphere	Recall questions on where ozone sits, the equations that form and destroy it naturally, the steady state, and ozone at ground level.	21
Radiation of the Earth and the Sun	Recall questions on how the radiation the Earth receives differs from what it emits, and which regions of the spectrum do what.	16
Effects of UV and visible radiation on molecules	Recall questions on what absorption does to a molecule, why ultraviolet causes chemical change when infrared does not, and why one photon must carry the energy.	17
Calculations with frequency, wavelength and energy	Recall questions on the relationships linking speed, frequency, wavelength and photon energy, and converting a photon energy to kJ mol⁻¹.	22

The Ozone Story is 355 of the 3,430 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.