Alfred Ajibola
- 22nd September, 2026 @ 08:39 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
A base can be defined via a variety of ways. These definitions are explained below (with chemical equations) through three main theories. They are:
1. Arrhenius Theory
A base is defined a substance that produces hydroxide ions (OH-) as the only negative ions when dissolved in water. This is shown via the equations below:
NaOH(aq) → Na+(aq) + OH-(aq)
Ca(OH)2(aq) → Ca2+(aq) + 2OH-(aq)
NaHCO3(aq) → Na+(aq) + HCO3-(aq)
Examples of bases include sodium hydroxide (NaOH), potassium bicarbonate (KHCO3), calcium hydroxide Ca(OH)2 and ammonia NH3.
2. Brønsted–Lowry Theory
A base is defined as a substance that accepts hydrogen ion or a proton (H+) from another substance.
To accept a proton, a Brønsted-Lowry base usually has a lone pair of electrons available to form a new chemical bond with the incoming hydrogen ion (or proton).
When a base accepts a proton, it becomes a conjugate acid, which can potentially give that proton back in a reverse reaction. This is expressed via the equation below:
From the above equation, when ammonia is dissolved in water, it acts as a Brønsted-Lowry base by accepting a proton from water (the acid). After accepting a proton from the acid (H2O), It forms a conjugate acid NH4+.
Note: The acid (H2O) in the above equation donates a proton to NH3 to become its conjugate base (OH-).
Please read on the definitions of acids, basicity and types of acid here.
3. Lewis Theory
A Lewis base is any chemical species that can donate a pair of electrons to form a coordinate covalent bond. In this definition, the:
Lewis base is the electron-pair donor (nucleophile)
Lewis acid is the electron-pair acceptor (electrophile).
Result: A coordinate covalent bond is formed, termed an adduct.
The equation below show Lewis definition of a base:
Lewis Base + Lewis Acid -> Adduct
HCO3- + H+(aq) ⇌ H2CO3(aq)
From the above equation, one of the lone electron pairs on the oxygen atom of HCO3- forms a new coordinate covalent bond with the electron-deficient hydrogen ion (H+), leading to the formation of carbonic acid (H2CO3).
Note: A base reacts with an acid to form a salt and water only. This reaction is termed neutralization reaction. Bases are typically metal oxides, metal hydroxides, or ammonia. This is shown via the equation below:
CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l)
NH3(aq) + H+(aq) → NH4+ (ammonia accepting a proton to form ammonium ion)
Please read on salts in chemistry here.
An alkali is a base that is soluble in water, forming a solution that contains a high concentration of hydroxide ions, OH-(aq). Simply put, an alkali is a soluble base. This is shown via the equation below:
All alkalis are bases, but not all bases are alkalis. A base is only considered an alkali if it actually dissolves in water. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide Ca(OH)2 are alkali since they dissolve in water. However, note that Ca(OH)2 dissolves only slightly in water.
Please read on the preparation of bases, test and uses here.
Bases are classified via the following ways:
They are put into organic and inorganic bases.
Organic vs Inorganic Bases
Organic bases are nitrogen-containing organic compounds that behave as bases due to a lone pair of electrons present on nitrogen (which is able to accept a proton or H+). They are generally weak bases.
Examples of organic bases include amines (e.g. methylamine, CH3NH2), and biological compounds like amino acids (which have basic –NH2 groups), and naturally occurring, nitrogen-containing basic plant compounds (alkaloids), e.g. caffeine, nicotine and morphine.
Inorganic bases not derived from living organisms. They are typically metal oxides, metal hydroxides, or ammonia; and can be strong or weak, soluble (alkalis) or insoluble.
Examples of inorganic bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide Ca(OH)2, copper(II) oxide (CuO), magnesium oxide (MgO), ammonia (NH3), zinc oxide (ZnO), etc.
You can read on periodic table and classification of elements here.
They are put into strong and weak bases.
Strong vs Weak Bases
Strong bases are bases that ionize or dissociate almost completely in water to release a high concentration of OH- ions. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide Ca(OH)2. This is shown via the equation below:
NaOH(aq) → Na+(aq) + OH-(aq) (essentially completely dissociation)
Ca(OH)2(aq) → Ca2+(aq) + 2OH-(aq)
Weak bases are bases that ionize only partially in water, establishing an equilibrium, and as a result, only a small fraction of the base is converted to ions at any point in time. Examples include ammonia solution (NH3(aq)), and most organic amines. The dissociation of a weak base is shown via the reversible reaction below:
Please read an introduction to chemical (dynamic) equilibrium in chemistry here.
Note: The classification of bases as strong and weak applies specifically to alkalis, i.e. bases soluble enough to test ionization in solution. Insoluble bases like CuO, MgO are not usually described as "strong" or "weak" in the same ionization sense, since they don't significantly dissolve to release ions in the first place.
They are put into concentrated and dilute bases.
Concentrated vs Dilute Bases
Just as with acids, concentration regarding bases (and alkalis) refers to the amount of base dissolved per unit volume of solution.
The concentration of a base is a separate property from the strength of a base (i.e, degree of ionization).
Concentrated bases contain a high proportion of base relative to water. Simply put it contain very little water and more base. An example of a concentrated base is molten sodium hydroxide solution, or fused NaOH.
Dilute bases contain a high proportion of water relative to base. Simply put, it contains excess water and little base. An example of a dilute base is dilute ammonia solution which is commonly used in the laboratory.
Note: As with acids, it is possible to have a dilute strong base (e.g. dilute NaOH since it still fully dissociates into ions, except that only just less of the base is present). It is also possible to have a concentrated weak base (e.g. concentrated ammonia solution which will still only partially ionizes even though it contains a large amount of the base, i.e, at high concentration).
Caution: Concentrated strong alkalis like concentrated NaOH are extremely corrosive and dangerous to handle, often more damaging to skin/eyes than acids of similar concentration, as they can cause deep tissue damage.
Please read on the physical and chemical properties of acids, test and uses of acids here.
Bases/alkalis generally have a bitter taste. They also feel soapy or slippery to the hands when touched. In this regard, they should never be tasted or touched directly in the laboratory.
They turn red litmus paper blue. A red litmus paper turns blue when dipped in a basic or alkaline solution.
Alkalis (soluble bases) conduct electricity in aqueous solution due to free-moving ions.
Most solid bases (e.g. NaOH and KOH) are deliquescent; that is: they absorb moisture from the air and dissolve (or turn into solution).
With the exception of sodium, potassium and calcium, most metal oxides/hydroxides are insoluble bases and solids at room temperature.
Ammonia is a pungent gas with a sharp and suffocating smell. It is a base that dissolves in water to form an alkaline solution.
Bases and alkaline solutions have a pH greater than 7, and up to pH 14 for strong concentrated alkalis.
You can read on the physical property of matter here.
1. Reaction with acids (neutralization)
Bases reacts with acids to form a salt and water only. This reaction is termed neutralization reaction. It is shown via the equations below:
Base + Acid → Salt + Water
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
2. Reaction with ammonium salts
When heated, bases react with ammonium salts to release ammonia gas. This is shown via the equation below:
3. Reaction with amphoteric metals
Amphoteric metals are chemical elements whose oxides and hydroxides can react with both acids and bases to form complex salts. Examples of amphoteric metals include zinc, aluminum and lead.
Alkalis can react with these metals to release hydrogen gas, forming a complex salt (as this is a special property of amphoteric metals, not typical of most metals). This is shown via the equation below:
Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g) (sodium zincate and hydrogen gas)
2Al(s) + 2NaOH(aq) + H2O(l) → 2NaAl(OH)4(aq) + 3H2(g)
You can attempt various questions (with answers) in chemistry here.
4. Reaction with non-metal (acidic) oxides
Non-metallic oxides are acidic oxides and gases (at room temperature). Examples of non-metallic oxides include CO2 and SO2. Bases can absorb or react with these acidic gases to form salt and water.
The equations below shows the reaction of bases with acidic (or non-metallic) oxides:
Base + Non-metallic oxide -> Salt + Water
2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l)
Ca(OH)2(aq) + SO3(g) → CaSO4(aq) + H2O(l)
5. Reactions with metal salt solutions
The reaction of alkalis with metal salt solution is a precipitation reaction since an insoluble metal hydroxide precipitate (solid) is formed. This is shown via the equations below:
CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)
FeCl3(aq) + 3KOH(aq) → Fe(OH)3(s) + 3KCl(aq)
Note: In the above reactions, Cu(OH)2(s) and Fe(OH)3(s) are precipitates (or insoluble solids in solution). The color of the precipitates can help us identify the metal ion present.
6. Effect on indicators
Bases change the color of acid-base indicators. This is summarized via the table below:
You can read on Boyle's law in chemistry here.
| Indicator | Color in Base/Alkali |
| Red litmus | Turns blue |
| Blue litmus | Stays blue (no change) |
| Methyl orange | Yellow |
| Phenolphthalein | Pink/magenta |
| Universal indicator | Blue to purple (pH > 7) |
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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:
