GCE Chemistry

Many students should already have studied this topic at IGCSE or IBMYP. A-Level is very similar in terms of content and question style. Calculating moles is therefore an easier topic to get marks in. Students can make a checklist of all the mathematical relationships regarding mole. You can then classify the data provided by the question and substitute them into the equations.

In this topic, students learn about atomic structure and the periodic table. To gain more marks you need to memorise chemical terms and their definitions: e.g. isotopes, relative molecular mass, the spectrometer’s inner components, ionisation energy, etc. Exam questions on topic 2 are easy to get marks in, but require your time and effort to memorise definitions. Besides definitions, you should also make a checklist for periodic trends since this is frequently asked in the exam.

Students will learn some difficult concepts here: electronegativity, polarising power, polarisability, etc. If you want a B or C, certain areas need more attention. For example, focus on familiarising yourself with the ionic structure and covalent structure; you must be able to draw them well. Practice dot and cross diagrams, Lewis structure, and molecular geometry, as they are an important foundation to understand harder concept in the upcoming topics

Topic 4 focuses on organic chemistry, especially alkanes, which are a particular class of hydrocarbons. The easiest way to get marks here is by revising alkanes’ free radical substitution mechanism. Exam questions related to this mechanism are usually the same each year, with students having to write these few equations. Also, it is necessary to classify the chemical equations provided into three different steps in the mechanism - i.e. Initiation, Propagation and Termination.

Alkenes are another class of hydrocarbons. Here are the most important areas to learn in order to get marks:Alkenes are another class of hydrocarbons. Here are the most important areas to learn in order to get marks:

• Alkenes have 5 different addition reactions; students should revise these 5 reactions, what reagents and conditions are used, and what products are produced.
• Practice drawing electrophilic addition reaction mechanisms until you can do it confidently.

Exam questions are generally the same each year for the subjects above.

• Understand how to determine the chemical structure of the major product, according to the stability of carbocation intermediate.

Energetics is a relatively difficult topic which involves equations and calculations. However, you can still get some easy marks.

• The 6 definitions you need to know are: enthalpy change of reaction, formation enthalpy, combustion enthalpy, neutralization enthalpy, atomization enthalpy and mean bond enthalpy.
• The meaning of standard condition
• The 3 types of calculations you will likely encounter are:
1. Experiment questions, using E = mc∆T to calculate the experiment’s enthalpy change. Pay attention to the units used in these equations
2. Hess’ Law, calculating a specific reaction’s enthalpy change.
3. Enthalpy change of reaction = Bond break - Bond form

Students need to memorise the 3 major types of intermolecular forces, including London dispersion force, dipole-dipole, and Hydrogen bond. You must know how they arise between molecules.

Additionally, students should recognise that there are 3 important molecules that include a hydrogen bond - water, ammonia, and hydrogen fluoride. If you see any of these 3, you must immediately know they have a hydrogen bond.

Students are frequently asked about the factor that affects the physical properties of compounds, and they are mainly affected by the strength of intermolecular forces. In these kinds of questions, there are three significant requirements to fulfil:

1. Point out what kind of intermolecular force they have.
2. Compare what kind of intermolecular force is stronger (by comparing the type of intermolecular forces, molecular size and contact surface area).
3. State that the stronger intermolecular force needs more energy to break down the forces; so, the boiling point/melting point will be higher.

Here, the easiest way to get marks is by knowing how to calculate different substances’ oxidation number. Then, use the changes in oxidation number to interpret which of the element in the reaction oxidized or reduced.

Another way to get straightforward marks is by memorising how group 1 and group 2 oxides react with water or acid, and knowing the chemical equations associated with each.

The most common topic within kinetics is undoubtedly collision theory, while the Le Chatelier’s principle is the area you are most likely to be asked in equilibriums. Make sure you can explain why different factors like concentration, temperature, pressure or surface area, will result in the rate and yield of reaction being different. If you use past paper exams and mark schemes to revise the sentence patterns well, you can get the marks easily in these kinds of questions.

Moreover, students must be able to recognise the Maxwell-Bowman diagram and know the shapes of the curves. Exams may ask you to redraw these graphs.

You will also have to understand how the reaction conditions for industrial processes are decided based on the compromise between rate and yield of reaction.

Topic 10 is comparatively more challenging and covers a lot of ground. Even so, there are some common questions that always pop up, such as oxidation of alcohol. Students have to understand the differences between the experimental techniques of distillation and reflux.

Another important question type will be in relation to the reaction mechanism of nucleophilic substitution. Learn the standardised way to draw them.

In terms of analytical techniques for organic compounds, you will have to analyze the IR spectrum and mass spectrum. Remember that the IR spectrum is used in determining bond type and functional group, while the mass spectrum is used for organic structure determination.

Questions concerning advanced kinetics tend to be more complex, so focus on the places you can definitely get marks in. For example, students must be able to select and justify the correct experimental techniques to find the rate of reaction. You could use titration, colorimetry, mass change, volume of gas involved, etc. to find easy answers. However, you must know which type of reaction matches with which method.

You will also have to compare the graphs for the chemicals with different orders of reaction. Similarly, understanding that the slope of “ln k - 1/T graphs” = -Ea/R for activation energy determination is an easy way to get marks.

You must know a few, less common, enthalpy definitions. They are lattice enthalpy, hydration enthalpy and solution enthalpy. Also, students will be required to calculate enthalpy changes based on the Born Haber Cycle and Solution Cycle.

Besides enthalpy changes, entropy change is another main focus of this topic. There are three equations for entropy changes

1. Entropy of system = entropy of products - entropy of reactants
2. Entropy of surrounding = -∆H/T
3. Total entropy change = entropy of system + entropy of surrounding

From the calculated total entropy change, students can determine whether the reaction is feasible or not at a particular temperature.

In topic 13, students should be able to calculate the equilibrium constant, including Kc and Kp. They should also know the difference between Kc and Kp.

For Kc, remember that students must use the equilibrium concentration to do their equations. It is not possible to use initial concentration, or anything other than equilibrium concentration, to calculate your answer.

For Kp, remember how it differs from Kc. P stands for partial pressure. When calculating Kp you cannot put concentration into your calculations. You need to find each reaction or product and the partial pressure of each gas reactant and product to put into your calculations to find Kp.

Also, do not forget how to deduce the unit for all equilibrium constants in this topic

Topic 14 also contains many definitions to memorise but also the opportunity for easy marks. A few of the most commonly asked definitions are as follows: What is Brønsted-Lowry acids and bases? What is pH? What is the strength of strong and weak acids? What is a buffer solution? You are also required to identify conjugate acid and base pair in a reaction. By using equilibrium concept, you can identify the color change of indicator during titration as well.

Review these five reactions and chemical tests of carbonyl compounds closely, including the chemical equations and positive observations:

1. Carbonyl compound reactions, including Fehling’s solution, Benedict’s solution, and Tollens reagent.
2. Adding lithium aluminium hydride to reduce aldehydes and ketones.
3. Adding potassium cyanide and hydrogen cyanide to create an nucleophilic addition reaction (*practice more about the reaction mechanism of this reaction as well).
4. Conducting a 2,4-Dinitrophenylhydrazine test, to examine whether a substance is or is not a carbonyl compound.
5. Conducting an iodoform test.

This topic goes over organic reactions of carboxylic acid, including:

1. Reduction by lithium aluminium hydride
2. Addition of base to produce salt
3. Addition of phosphorus trichloride to produce an acyl chloride.
4. Addition of alcohol to make an ester.

For all the above reactions, you must remember their reagents, conditions, and know how to name the products to get full marks.

It is important for students to know the common definitions, e.g. ligand, coordinate bond (aka. dative covalent bond), coordination number, etc. Also, make sure you are able to explain why transition metals all have different colours. A good example answer explains the splitting of d-orbital and absorption of energy, which promotes it to a high energy level, resulting in transmission of some visible complementary colours. It is important to memorize the colors of some typical transition metal ion, such as iron (II), iron (III), copper (II), manganese (II), chromium (III). Acid base behavior of these transition metal ions are frequently asked as well, based on the observation after addition of sodium hydroxide and ammonia solution.

Here, remember at least one physical evidence and chemical evidence, respectively, which shows the delocalization of electrons in the benzene ring. the benzene chemical reactions including combustion, bromination, nitration, sulphonation, and Friedal-Crafts reaction. You must know how to write each reaction out, with the matching reagents, catalysts, and reaction conditions.

Another common question regarding reaction mechanisms is electrophilic substitution of benzene. Remember the name and reaction mechanisms.

This final topic includes reactions of organic nitrogen compounds. There are 5 major types of reactions involving amine that you should know:

1. Adding water
2. Adding acid
3. Adding halogenoalkane (nucleophilic substitution)
4. Adding ethanoyl chloride (nucleophilic addition elimination)
5. Adding copper (II) ions.

Students should know what products will result from adding each of these substances. We can use the reaction mechanism learnt before to explain the organic reactions that happen in this section.