Alfred Ajibola
- 16th September, 2026 @ 04:38 PM
Topics in Chemistry
Chemistry Scheme of Work, SS1 Third Term Chemical Industries: Petrochemicals, Biodegradable, Non-biodegradable Wastes and Pollutants Chemical Industries: Types, Advantages, Disadvantages and Factors affecting Chemical Industries Hydrocarbons: Fractional Distillation of Crude oil and Uses of its Fractions Hydrocarbons: Sources, Classification and Test for Saturated and Unsaturated Hydrocarbons Trioxocarbonates: Preparation, Physical and Chemical Properties, Tests and Uses of Trioxocarbonates Carbon and its Compounds: Oxides of Carbon, Carbon(IV) oxide Carbon and its Compounds: Oxides of Carbon Amorphous Allotropes of Carbon Carbon: Structure and Allotropes of Carbon Salts in Chemistry: Types, Properties, and Uses of Salts Salts in Chemistry, their Classifications, Solubility, Preparations and Colors pH Indicators, Types of Indicators and Importance of pH and pOH Relative Acidity and Alkalinity (pH Scale), and Calculations on pH Bases and Alkalis: Definitions, Classification, Physical and Chemical Properties Bases: Preparation of Bases and Alkalis, Test and Uses Physical and Chemical Properties of Acids, Preparation, Test and Uses of Acids. Acid: Definition, Basicity, and Types of Acid Families of elements in the periodic table Periodic table and Classification of ElementsAcademic Questions in Chemistry
With regards to redox reactions, which of the following statement is wrong?
A. Redox reaction are examples of chemical change
B. Reduction is the gain of electron
C. Substances that donates election during chemical reaction are termed reductants
D. Oxidizing agents are always reduced in chemical reactions
E. Oxidation occurs at the cathode in electrolysis
F. Hydrogen is a reducing agent
In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.
A. True
B. False
_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.
A. Outer
B. Excess
C. Valence
D. Positive
E. Negative
F. Last
_____ is the negative electrode in electrolysis.
A. Anode
B. Anion
C. Cathode
D. Cation
E. Ion
F. Electrolyte
The above diagram shows the _____ type of bond.
A. Covalent
B. Polar covalent
C. Coordinate covalent
D. Metallic
E. Van dear walls
F. Ionic
Metals are referred to as _____ in their impure state.
A. Diluted
B. Consecrated
C. Coloured
D. Ores
E. Stained
F. Strained
Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.
A. State
B. Ductility
C. Luster
D. Malleability
E. Hardness
F. Inflorescence
The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.
A. Mole
B. Volume
C. Weight
D. Number of moles
E. Mass
F. Amount of substance
Acids has been defined in a variety of ways by various scientist. At senior secondary level, the following definitions are commonly used; and these definitions are explained below:
1. Svante Arrhenius definition of acid
Svante Arrhenius defined an acid as any substance that produces hydrogen ion (H+) as the only positive ion when dissolved in water. In this regard, he stated that an acid refers to any substance that increases the concentration of hydrogen ions {H+), or protons, when dissolved in water.
The definition of Arrhenius acid is shown via the equations below:
HCl(aq) -> H+ + Cl-(aq)
HNO3(aq) -> H+ + NO3-(aq)
H2SO4(aq) -> 2H+ + SO42-(aq)
An acid is a substance that dissociates (or ionizes) in water to produce hydrogen ions, H+(aq) (or more accurately, hydroxonium or hydronium ions, H3O+) as the only positive ion.
The original definition of Arrhenius acid had been modified in modern chemistry. In this slight modification, an acid is defined as a substance that produces hydronium ion (or hydroxonium ion) as the only positive ion when dissolved in water. This is a better definition of an acid. It is shown via the equations below:
HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)
HNO3(g) + H2O(l) → H3O+(aq) + NO3-(aq)
H2SO4(aq) + 2H2O(l) → 2H3O+(aq) + SO42-(aq)
You can read on elements in chemistry here.
2. Brønsted Thomas Lowry Acid
Brønsted Thomas Lowry defined an acid as any substance that donates a proton to another substance (a base) in chemical reaction. A proton in chemistry refers to hydrogen ion (H+). The specie that donates a proton is a termed Brønsted Lowry acid, while that which accepts a proton, a Brønsted Lowry base.
When an acid loses a proton, it forms a conjugate base.The original acid and its resulting conjugate base are considered to work as a pair.
In the above equation, HCl is the Brønsted Lowry acid, and NaOH the Brønsted Lowry base. base. The OH that makes up the Brønsted Lowry base accepted a proton (H+) from the acid HCl, ultimately leading to the formation of H2O. This reaction between an acid and a base is termed neutralization reaction.
You can read on salts in chemistry here.
3. Gilbert Newton Lewis Acid
Gilbert Lewis defined an acid as any chemical specie that can accept a pair of electrons to form a coordinate covalent bond.
The Lewis acid is an electron-pair acceptor, and it usually possesses an empty orbital (or incomplete valence electron) on its shell. A Lewis base is an electron-pair donor, and it has a lone pair of electrons which it chan share. The product formed when a Lewis acid and a Lewis base bind together is termed an adduct. This is described below
Lewis Acid + Lewis Base -> Adduct
Below is an equation showing the Lewis acid and base reaction.
In the above reaction, ammonia (NH3) donates its lone pair of electrons, acting as the Lewis base, while boron trifluoride (BF3) accepts the electron pair into its empty orbital, thus acting as the Lewis acid.
Please read more on the definitions of acids here.
Note: An acid can also be defined in a simple operational and practical manner. In this regard, an acid is defined as a substance that shows the following properties:
Tastes sour (in dilute, solutions like food acids which is safe to taste).
Turns blue litmus paper red.
Has a pH lesser than 7.
Reacts with more reactive metals to liberate hydrogen gas.
Reacts with bases/alkalis in a neutralization reaction to form salt and water only.
Reacts with carbonates to liberate carbon(IV)oxide gas.
You can read the concept of salts in chemistry here.
Acids can be classified based on a variety of independent factors. These include::
Classification by Origin: These are organic and inorganic acid.
Classification by Degree of Ionization or Strength. These are strong and weak acid.
Classification by Concentration: These are concentrated and dilute acid.
Below are explanations of the above classification of acid.
Concentrated and Dilute Acids
When a small amount of water is added to a large amount of acid, the resulting acid solution is said to be concentrated. In this regard, a concentrated acid is defined as a solution that has a large amount of acid molecules and very little water. It therefore contains high ratio of acid to water. Concentrated acids are corrosive, and can thus burn the skin.
When large amount of water is added to a small amount of acid, the resulting solution is said to be dilute. In this regard, a dilite acid is defined as a solution that has a very little amount of acid molecules and very large amounts of water. It therefore contains low ratio of acid to water. Dilute Acids are not corrosive.
Note: Concentrated or dilute acid simply refers to the amount of acid dissolved relative to the amount of water in the solution, and it does not depend on the strength of the acid.
The concentration or dilution of acids should not be confused with pH. The term 'pH' stands for 'potential for hydrogen'. It is a measure of the amount of hydrogen ions (H+) in water; that is , the strength of the acid. It is used to measure how acidic or basic a liquid is.
Please read on mixtures and separation techniques here.
Strong and Weak Acids
This classification is based on the extent to which the acid ionizes (or dissociates) in water. In this regar, an acid is considered to be either strong or weak based on its strength (degree of ionization or dissociation in water); and not based on its concentration.
Strong acids refers to acids that ionizes almost completely in water, producing a high concentration of H⁺ ions for a given concentration of acid. Examples include hydrochloric acid (HCl), sulfuric acid (H2SO4) and nitric acid (HNO3). This is shown via the equation below:
HCl(aq) → H+(aq) + Cl-(aq) (It ionized essentially at 100%; and is denoted by its single forward arrow).
Weak acids refer to acids that ionizes only partially in water. During dissociation of a weak acid, an equilibrium is established between the un-ionized acid and its (ionized) ions, such that only a small fraction of the acid molecules are ionized at any time. Examples of weak acids include organic acids, e.g, ethanoic acid (CH3COOH), carbonic acid (H2CO3). H2S, H2CO3 and H3PO4 are inorganic weak acid.
The equation for the weak ionization of ethanoic acid is shown below:
CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq).(It is ionized partially as denoted by equilibrium, and thus, the double arrow)
Note: For solutions of the same concentration, strong acids are more acidic, have a lower pH, conduct electricity better (since more ions present), and react faster with metals and carbonates when compared to weak acids.
Please read on the physical and chemical properties of acids, test and uses of acids here.
Below are notable distinctions (differences) between strength and concentration of acids.
Strength refers to the degree of ionization of the acid in water (a fixed chemical property of a given acid), while concentration refers to the amount of acid dissolved in a given volume of solution (can be varied by adding/removing water).
It is possible to have a concentrated weak acid (e.g. glacial ethanoic acid, which is a nearly pure ethanoic acid, but still only partially ionizes), or a dilute strong acid (e.g. dilute hydrochloric acid used in the lab, which is still essentially 100% ionized despite being dilute).
You can read Dalton's atomic theory and its modifications here.
Organic and Inorganic Acids
The word organic primarily means relating to living organisms. In this regard, organic acids are derived from living organisms, and will contain carboxylic (or –COOH) functional groups. Organic acids are generally weak acids. Examples of organic acid include the following:
Ethanoic acid (CH3COOH). It is found in vinegar.
Citric acid, (C6H8O7). It is found in citrus fruits, e.g oranges and lemons.
Lactic acid, CH₃CH(OH)COOH. It is found in sour milk, and is also produced in muscles as a product of anaerobic respiration during strenuous exercise.
Tartaric acid is found in grapes. Malic acid id found in apples. Ascorbic acid (Vitamin C) is found in citrus fruits, while Oxalic acid is found in vegetables like spinach and rhubarb.
Inorganic Acids: They are called mineral acids, and are not derived from living organisms, but are rather manufactured from minerals. Inorganic acids can be strong or weak acids.
Examples of inorganic acids are hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), hydrobromic acid (HBr), hydroiodic acid (HI), chloric acid (HClO3), and perchloric acid (HClO4).
Examples of weak inorganic acid include carbonic acid (H2CO3), phosphoric(V) acid (H3PO4), trioxosulfate(IV) or sulfurous acid (H2SO3), Boric acid (H3BO3), Nitrous acid (HNO2) and Hydrocyanic acid (HCN)
You can read on gas laws in chemistry here.
Note: Acids are present in in various cells, tissues and organs of the human body. They include hydrochloric acid in gastric (stomach) juice which aids digestion, lactic acid produced in muscles during strenuous exercise (associated with muscle fatigue), amino acids as building blocks of proteins, nucleic acids (DNA/RNA) in cells, and uric acid, a waste product of metabolism.
Recall that the presence of hydrogen ion (H+) as the only positive ion in a molecule makes that molecule an acid. In this regard, the basicity of an acid is defined as the number of replaceable (or ionizablle) hydrogen ion (H+) present in one molecule of the acid, that is, the number of H+ ions that one molecule of the acid can release!or donate in a reaction.
Acids are classified into three different types depending on their basicity, that is: how many hydrogen ions a single molecule of acid can release (or can be replaced). Below are types of acid based on their basicity:
1. Monobasic Acid:
They are also called monoprotic acid. These acids contain only one replaceable hydrogen ion (H+) per molecule, giving it a basicity of 1. The react with a base in the mole ratio of 1:1. This is shown via the equation below:
HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)
Examples of monobasic acid include hydrochloric acid (HCl), trioxonitrate(V) acid (HNO3) and ethnoic acid (CH3COOH).
2. Dibasic Acid:
They are also called diprotic acid. These acids contain two replaceable hydrogen ions (2H+) per molecule, giving it a basicity of 2; and can sometimes be neutralized in two stages, forming an acid salt as an intermediate in the process. This is shown via the equations below:
Examples of dibasic acids include tetraoxosulphate(VI) acid (H2SO4), trioxocarbonate(IV) acid {H2CO3), and trioxosulfate(IV)/sulfurous acid (H2SO3).
3. Tribasic Acid:
They are also termed tripotic acids. These acids contains three replaceable hydrogen ions (3H+) per molecule, giving it a basicity of 3, and can sometimes be neutralized in three stages. This is shown via the equations below.
H3PO4(aq) + 3NaOH(aq) → Na3PO4(aq) + 3H2O(aq) (full neutralization)
H3PO4(aq) + NaOH(aq) → NaH2PO4(aq) + H2O(l) (first stage partial neutralization forming acid salt)
H3PO4(aq) + 2NaOH(aq) → Na2HPO4(aq) + H2O(l) (second stage partial neutralization forming acid salt)*
Examples of tribasic acids include tetraoxophosphate(V) acid, (H3PO4), citric acid (C6H8O7) and trioxoboric(III) acid (H3BO3).
You can attempt questions and answers in chemistry here.
The table below shows the basicity of acids:
| Basicity | Examples of Acid | H+ Liberated |
| Monobasic | HCl, HNO3, CH3COOH | 1 |
| Dibasic | H2SO4, H2CO3, H2C2O4 | 2 |
| Tribasic | H3PO4, H3BO3, C6H8O7 | 3 |
Note: Some acids have more than one hydrogen atom but not all of these in the acid molecule is ionizablle and replaceable. For example, ethanoic acid (CH3COOH) has four hydrogen atoms, but only one of these is replaced or ionized in water; therefore making its basicity 1 (monobasic). Also, citric acid (C6H8O7) has has eight hydrogen atoms, but only three of these can be replaced and ionizes in water; thus making its basicity 3 (tribasic).
Basicity depends strictly on the number of hydrogen ions (H+) liberated during dissociation, and not the total number of hydrogen atoms in the formula.
Please read chemistry SS1 note for week 2 here.
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Amazing facts in Chemistry
Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years
The only letters that failed to appear on the periodic table are letters:
Gold and copper are the only two non-silvery colored metals.
Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools
Water freezes faster when it’s warm than when it’s cold
Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy
If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.
Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre
Notable points in Chemistry
Below are the physical properties of metals:
They exist in solid state.
The have high densities.
They are good conductors of heat and electricity.
The have the ability to be polished, to glow, sparkle and reflect light.
They can be bent, flattened and made into sheets called foils.
They can be drawn into wires.
Iron undergoes magnetism while most metals are poorly magnetized.
They typical have high melting point.
They generally have high boiling point.
With the exception of lithium, sodium and potassium, most metals are generally hard.
They have the ability to make sound when in contact with other objects or metals.
Please read details on the physical properties of metals here
John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.
Below are Dalton's Atomic Theory:
All matter consists of tiny indivisible particles called atoms.
Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.
Atoms are indestructible and can neither be created nor destroyed.
Atoms of different elements can combine with each other in simple whole number ratios to form compounds.
Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.
Meanwhile, understand that the above theories of John Dalton had been modified.
Please read on Dalton's atomic theory and its modifications here
The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.
Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.
The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.
A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)
Step 1: Identify the given parameter from the question.
Fe = 69.94%, O = 30.06%.
Empirical formula = Fe?O?
Step 2: Convert the percentages to gram. (just attribute grams to the %).
Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.
Mole of Fe: 69.94/55.85 = 1.252mol
Mole of O: 30.06/16 = 1.879mol
Step 4: Divide both sides by the smallest mole ratio.
Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1, 1.879/1.252 = 1.5
We now have the formula = Fe1O1.5
Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.
For iron (Fe), we will have 1 x 2 = 2
For oxygen (O), we will have 1.5 x 2 = 3
Step 6: Write the empirical formula.
The empirical formula= Fe2O3
Iron(III)tetraoxosulphate(VI)
In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.
Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:
Alkanes
Alkenes
Alkynes
They are shown in the image below:
It's important to note the followings:
Alkanes have single bonds (only) in their structures.
Alkenes always have a carbon-carbon double bond present in their structure.
Alkynes always have a carbon-carbon triple bond present in their structure.
Aromatic hydrocarbons are classified into:
