WASSCE / WAEC Chemistry Objective Questions & Answers
Practice Quiz: Carbohydrates, Proteins, Fats and Oils
Theme 1: Carbohydrates
Question 1
Which of the following carbohydrates is classified as a disaccharide?
- A. Glucose
- B. Sucrose
- C. Cellulose
- D. Fructose
Correct Answer: B
Explanation: Sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$) is a disaccharide formed by the condensation of two monosaccharide units: glucose and fructose. Glucose and fructose are single monomer units (monosaccharides), while cellulose is a complex polysaccharide.
Question 2
The complete acid hydrolysis of starch yields which of the following monomers?
- A. Fructose
- B. Maltose
- C. Glucose
- D. Sucrose
Correct Answer: C
Explanation: Starch is a natural polymer made up of repeating $\alpha$-glucose units. When heated with dilute acid, the glycosidic linkages are completely broken down, yielding only glucose molecules.
Question 3
A sample of food substance turned blue-black when treated with a few drops of iodine solution. This observation confirms the presence of
- A. Glucose
- B. Reducing sugar
- C. Fatty acid
- D. Starch
Correct Answer: D
Explanation: The iodine test is a specific qualitative test for starch. Amylose in starch forms a characteristic deep blue-black insertion complex with iodine molecules. Monosaccharides like glucose do not react.
Question 4
Which of the following statements is a characteristic property of monosaccharides?
- A. They can be broken down into simpler sugars by hydrolysis
- B. They are highly insoluble in water
- C. They cannot be further hydrolyzed into simpler carbohydrates
- D. They fail to reduce Fehling's solution on heating
Correct Answer: C
Explanation: Monosaccharides are the simplest structural units of carbohydrates. Because they are already monomers, they cannot be broken down into smaller carbohydrate molecules by water or acid hydrolysis.
Theme 2: Proteins
Question 5
The two functional groups present in all amino acid monomers are
- A. Hydroxyl and Carboxyl groups
- B. Amino and Carboxyl groups
- C. Amide and Ester groups
- D. Amino and Alkyl groups
Correct Answer: B
Explanation: As the name implies, every amino acid contains a basic amino group ($-\text{NH}_2$) and an acidic carboxylic acid group ($-\text{COOH}$) bound to the same central alpha-carbon.
Question 6
The specific linkage that holds amino acid units together in a polypeptide or protein is the
- A. Glycosidic bond
- B. Ester bond
- C. Peptide bond
- D. Hydrogen bond
Correct Answer: C
Explanation: Amino acids polymerize via condensation reactions to form peptide bonds ($-\text{CO}-\text{NH}-$). Glycosidic bonds are found in carbohydrates, and ester bonds are found in fats and oils.
Question 7
The irreversible coagulation of egg white albumin when heated during boiling is an example of protein
- A. Denaturation
- B. Hydrolysis
- C. Saponification
- D. Hydrogenation
Correct Answer: A
Explanation: Denaturation is the disruption of a protein's native three-dimensional conformation (secondary, tertiary, or quaternary structure) by physical factors like heat. It alters its properties without breaking the primary peptide bonds.
Question 8
Which of the following test reagents yields a violet or purple coloration to confirm the presence of proteins?
- A. Benedict's reagent
- B. Biuret reagent
- C. Iodine solution
- D. Freshly prepared $\text{FeSO}_4$ solution
Correct Answer: B
Explanation: The Biuret test detects peptide links. Treating a protein solution with dilute sodium hydroxide ($\text{NaOH}$) and a few drops of copper(II) sulfate ($\text{CuSO}_4$) creates a coordination complex that appears violet or purple.
Theme 3: Fats and Oils
Question 9
From a chemical standpoint, natural fats and oils are classified as
- A. Simple hydrocarbons
- B. Long-chain alkanols
- C. Esters of glycerol and fatty acids
- D. Carbohydrate derivatives
Correct Answer: C
Explanation: Fats and oils are triglycerides. They are formed through an esterification reaction linking one molecule of propane-1,2,3-triol (glycerol) with three molecules of long-chain carboxylic acids (fatty acids).
Question 10
Vegetable oils are liquid at room temperature because their structural chains possess
- A. Only single carbon-to-carbon bonds
- B. A high degree of unsaturation with carbon-to-carbon double bonds
- C. Very short hydrocarbon branches
- D. High molecular weight ionic clusters
Correct Answer: B
Explanation: The presence of carbon-to-carbon double bonds ($\text{C}=\text{C}$) in vegetable oils introduces kinks in the fatty acid chains, preventing tight molecular packing. This keeps their melting points low, making them liquids at room temperature.
Question 11
The commercial process of boiling fats or oils with an alkali like sodium hydroxide to produce soap is termed
- A. Esterification
- B. Saponification
- C. Fermentation
- D. Dehydration
Correct Answer: B
Explanation: Saponification is the alkaline hydrolysis of an ester. When a lipid is heated with $\text{NaOH}$, it breaks down into glycerol and sodium salts of fatty acids, which is what we call soap.
Question 12
In the food manufacturing industry, liquid vegetable oils are hardened into solid margarine through hydrogenation using
- A. Hydrogen gas and a finely divided Nickel catalyst
- B. Oxygen gas and a Platinum catalyst
- C. Nitrogen gas and an Iron catalyst
- D. Carbon monoxide gas and a Copper catalyst
Correct Answer: A
Explanation: Industrial hardening of oils involves adding hydrogen gas ($\text{H}_2$) across the unsaturated double bonds to make them saturated single bonds. This raising of the melting point requires a heated, finely divided **Nickel ($\text{Ni}$)** catalyst.
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