Alfred Ajibola
- 29th September, 2026 @ 01:35 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
An indicator is a substance (usually a weak organic acid or base) that changes color depending on the pH of the solution it is added to, and is therefore used to detect or estimate whether a solution is acidic, neutral, or alkaline; and in titrations, to signal the end-point (or equivalence point) of a neutralization reaction.
Indicators work because they exist in two (or more) differently colored forms; that is; one predominant in acidic conditions and another in alkaline conditions, with the color change occurring around a specific pH range characteristic of that indicator.
Different indicators show different colors in acidic and alkaline media.
Please read an introduction to acids, basicity and types of acids here.
The table below show the colors of indicators in different media:
| Indicator | Color in Acid | Color in Neutral | Color in Alkali | Approx. pH range of color change |
| Litmus | Red | Purple | Blue | ~5–8 |
| Methyl orange | Red | Orange | Yellow | ~3.1–4.4 |
|
Phenolp- hthalein |
Colorless | Colorless | Pink or magenta | ~8.2–10 |
| Universal indicator | Red or orange (low pH) | Green (pH 7) | Blue or purple (high pH) | 0–14 (full range) |
| Methyl red | Red | Orange | Yellow | ~4.4–6.2 |
| Bromothymol blue | Yellow | Green | Blue | ~6.0–7.6 |
Note: Universal indicator is a mixture of several indicators, designed to give a continuous range of colors across the whole pH scale, compared against a standard reference chart. On the other hand, single indicators such as litmus or phenolphthalein shows only one color change over a narrow pH range.
We have two types of indicators. These are natural Indicators and synthetic indicators.
Please read the introduction to pH scale (relative acidity and alkalinity) here.
Natural Indicators are indicators obtained from natural sources (mainly plants). They were often used traditionally before synthetic indicators were developed. Examples of natural Indicators include:
1. Litmus
It is extracted from lichen (algae and fungus). It turns red when dipped in acid, and blue in alkali. Litmus is probably the most well-known natural indicator, though it is now often manufactured and purified for laboratory use.
The table below show a summary of the color change of a litmus paper when dipped in acid or base.
| Litmus Paper | Color change when dipped in acid or base |
| Blue litmus paper |
Turns red in acids but remains blue in bases |
| Red litmus paper | Remains red in acids but turns blue in bases |
| Neutral litmus paper | It has a purple when dry, turning red in acids and blue in bases |
Please read on preparation of bases and alkalis, test and uses here.
2. Red cabbage extract (anthocyanin)
It changes through a range of colors. It turns red in strong acid,.pink in weak acids, , purple/blue near neutral, and green/yellow in bases. It is commonly used in simple school experiments.
The table below show a summary of the color change of a red cabbage extract.
| pH Value | Color | Solution Type |
| pH 2 | Dark Pink / Red | Strong Acid |
| pH 3 | Rose / Pink | Acid |
| pH 4 | Lavender / Red-Purple | Weak Acid |
| pH 5–6 | Purple / Violet | Weak Acid / Neutral approach |
| pH 7 |
Purple / Blue-Violet |
Neutral (e.g., pure water) |
| pH 8 | Blue | Weak Base / Neutral approach |
| pH 9 | Blue-Green / Teal | Weak Base |
| pH 10 | Emerald Green | Moderate Base |
| pH 11–12 | Greenish-Yellow | Strong Base |
Please read on the physical and chemical properties of acids, test and uses here.
3. Turmeric
It turns from yellow (in acid/neutral) to reddish-brown (in alkali).
In Acid: The color remains yellow. Adding an acid like lemon juice or vinegar to turmeric will not change its natural yellow shade.
In a Neutral solution like pure water: The color stays yellow.
In Base: The color changes to reddish-brown. Adding a basic substance like soap, detergent, or baking soda triggers this change.
The table below show a summary of the color change of a tumeric in an acidic, basic and neutral solution:
| Solution Type | Color Change |
| Acid | Yellow (No change) |
| Water (Neutral) | Yellow (No change) |
| Base | Reddish pink, Red-orange, Reddish brown or Red |
You can attempt various questions with answers in chemistry here.
These are indicators manufactured chemically in a laboratory or industrial setting, generally giving sharper, more precisely defined color changes at specific pH ranges. For this reason, they are more reliable for accurate titration work than natural Indicators.
Examples of synthetic indicators include phenolphthalein, methyl orange, methyl red, bromothymol blue and universal indicator.
A universal indicator is a synthetic mixture of several indicator dyes.
The table below show the colors of various synthetic indicators in an acidic, neutral, and alkaline medium, alongside their approximate pH.
| Indicator | Color in Acid | Color in Neutral | Color in Alkali | Approx. pH range of color change |
| Methyl orange | Red | Orange | Yellow | ~3.1–4.4 |
|
Phenolp- hthalein |
Colorless | Colorless | Pink or magenta | ~8.2–10 |
| Universal indicator | Red pr orange (low pH) | Green (pH 7) | Blue or purple (high pH) | 0–14 (full range) |
| Methyl red | Red | Orange | Yellow | ~4.4–6.2 |
| Bromothymol blue | Yellow | Green | Blue | ~6.0–7.6 |
You can read on the families of elements in the periodic table here.
They are more consistent with their color change and results.
They have sharper color transitions.
They have a well-defined and documented pH ranges.
The have longer shelf life.
They are more suitable for precise analytical/titration work in industry and research labs.
Note: Natural indicators remain useful for simple qualitative demonstrations, since they are cheap, readily available, and environmentally friendly.
Please read on the adverse effects of chemistry here.
pH is applied in our daily life under the following headings:
1. Human body
Blood pH must be maintained within a narrow range (~7.35–7.45). Deviations from this narrow range can cause serious illness. Also, stomach acid has a low pH (~1.5–3.5) to aid digestion, while saliva and other body fluids have their own optimal pH ranges.
Please read more on homeostasis here.
2. Skin and hair care products
Soaps, shampoos, and cosmetics are formulated at specific pH levels (often close to the skin's natural slightly acidic pH, ~5.5) to avoid irritation.
3. Food and drinks
pH affects taste, preservation, and safety of food through processes like pickling.
Pickling is a method of extending the shelf life of food by submerging it in an acidic liquid like vinegar, or through anaerobic fermentation in a salt brine.
Pickling relies on low pH to prevent bacterial growth. In this regard, monitoring pH is important in food and beverage quality control.
5. Gardening/agriculture
Soil pH affects nutrient availability to plants. In this regard, farmers test and adjust soil pH (e.g. adding lime to raise pH of acidic soils) for optimal crop growth. For example, cranberries, blueberries and potatoes thrives in acidic soils between the pH 4.5 - 5.5, while crops like barley, sorghum and sugar beet thrives best in alkaline environments.
You can read on soil composition here.
5. Aquariums and fish farming
Water pH must be maintained within a suitable range for aquatic organisms to survive. For example, most sea organisms thrive best in an alkaline pH.
6. Swimming pools
pH must be carefully controlled (usually between the range: 7.2–7.8) for swimmer comfort, safety and effective chlorine disinfection.
Please read on the uses of chemistry here.
1. Pharmaceutical industry
Most drugs are formulated at a specific pH for stability, absorption, and effectiveness in the treatment of diseases.
2. Water treatment
pH monitoring and adjustment is essential in treating drinking water and wastewater, both to ensure safety and to optimize disinfection and coagulation processes.
3. Chemical manufacturing
Many industrial reactions require precise pH control for optimal yield and to avoid unwanted side reactions or equipment corrosion.
4. Textile and dye industries
Dyeing processes are highly pH-dependent for proper color fixation.
Please read on separation techniques of mixtures here.
5. Food processing industry
pH control is crucial in fermentation (e.g. brewing, dairy production), preservation, and canning to prevent spoilage, while also ensuring food safety.
6. Environmental monitoring
Measuring the pH of rivers, lakes, and rainwater helps to monitor pollution (e.g. acid rain) and its consequent impact on ecosystems.
7. Corrosion control
The pH of process water in boilers/pipelines can be measured and controlled to reduce corrosion of metal equipment.
8. Agriculture/fertilizer industry
Monitoring and adjusting soil pH can improve crop yield. For instance, adding lime can help raise the pH of acidic soils (making it alkaline) for optimal growth of crops like barley and sorghum. On the other hand, addition of elemental sulphur can lower a soil's pH (making it acidic) for optimal growth of crops like cranberries and blueberries.
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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:
