WAEC chemistry: 10 Key Topics that WAEC set every year with some worked examples

Firstly I will implore all the waec candidate reading this article to follow and comment for regular and more update in different subject as regards 2020 WAEC Examination.

Chemistry is one of the core subject which all the secondary school science students should pass before they can gain admission in their various higher institution of choice.

At least last credit should be obtained i.e C6.

It has been visible to the blinds that WAEC start on 17th of August.

Here are the 10 key Topics in chemistry all science students need to prepared for before going into the end of hall.

1 pH and pOH

pH is a measure of hydrogen ion concentration, a measure of the acidity or alkalinity of a solution.

The pH scale usually ranges from 0 to 14. Aqueous solutions at 25°C with a pH less than 7 are acidic, while those with a pH greater

than 7 are basic or alkaline.

A pH level of 7.0 at 25°C is defined as “neutral” because the concentration of H O equals the concentration of OH in pure water. Very strong acids might have a negative pH, while very strong bases might have a pH greater than 14.

pOH

pOH is a measure of hydroxide ion (OH-) concentration. It is used to express the alkalinity of a solution. Aqueous solutions at 25 degrees Celcius with pOH less than 7 are alkaline, pOH greater than 7 are acidic and pOH equal to 7 are neutral.

2 Electronic Configuration

The electron configuration of an atom is written with the help of subshell labels. These labels contain the shell number (given by the principal quantum number), the subshell name (given by the azimuthal quantum number), and the total number of electrons in the subshell in superscript.

3 State of Matter ( Solid, Liquid and Gas)

Solid

In a solid, constituent particles (ions, atoms, or molecules) are closely packed together. The forces between particles are so strong that the particles cannot move freely but can only vibrate.

As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by an outside force, as when broken or cut. In crystalline solids , the particles (atoms, molecules, or ions) are packed in a regularly ordered, repeating pattern.

There are various different crystal structures , and the same substance can have more than one structure (or solid phase). For example, iron has a body-centred cubic structure at temperatures below 912 °C (1,674 °F), and a face-centred cubic structure between 912 and 1,394 °C (2,541 °F). Ice has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures.

Liquid

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if the temperature and pressure are constant. 

GAS

A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.

In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas ), and the typical distance between neighboring molecules is much greater than the molecular size.

4

Ideal Gas Law

The ideal gas law , also called the general gas equation , is the equation of state of a hypothetical ideal gas .

It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stated by Benoit Paul Emile Clapeyron in 1834 as a combination of the empirical Boyle’s law , Charles’s law, Avogadro’s law , and Gay-Lussac’s law .

The ideal gas law is often written in an empirical form:

5 Entalpy change

Enthalpy change is the name given to the amount of heat evolved or absorbed in a reaction carried out at constant pressure. It is given the symbol ΔH, read as” delta H”.

6 Redox Reaction

Redox reactions can occur relatively slowly, as in the formation of rust , or much more rapidly, as in the case of burning fuel. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), and more complex processes such as the oxidation of glucose (C 6 H 12 O 6 ) in the human body. Analysis of bond energies and ionization energies in water allow calculation of the redox potentials. 

7 Electrolysis

Electrolysis , process by which electric current is passed through a substance to effect a chemical change.

The chemical change is one in which the substance loses or gains an electron (oxidation or reduction). The process is carried out in an electrolytic cell , an apparatus consisting of positive and negative electrodes held apart and dipped into a solution containing positively and negatively charged ions. 

8 Homologous series

A homologous series is a family of hydrocarbons with similar chemical properties who share the same general formula.

We will look at three hydrocarbon series: alkanes, alkenes and the cycloalkanes. Hydrocarbons are compounds that contain only hydrogen and carbon

9 Benzene

Benzene is an organic chemical compound with the

molecular formula C 6 H 6 . The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon .

10 Alkanols

Alkanol. Aliphatic alcohols represent a family of organic compounds containing one or more hydroxyl group (–OH) bonded to an alkyl.

Alkanols belong to a group of organic (carbon) compounds known as alcohols. · Alcohols contain the OH, hydroxyl 

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