Hello students! My name is Francis, and in today’s chemistry class on AllCBTs, we’re diving into common organic chemistry questions. These questions are popular in WAEC, NECO, JAMB, and GCE exams, especially in the organic chemistry section.
So grab your writing materials and let’s begin this powerful revision session. You’ll learn:
- How to identify key organic compounds
- Common chemical tests and reactions
- What to expect in your 2025 Chemistry exams
You can watch the full class in the video below:
Question 1: Test for the Presence of Alkenes
How can you test for the presence of an alkene?
Answer: Use bromine water.
Explanation:
Alkenes are unsaturated hydrocarbons (they have carbon-carbon double bonds). When bromine water is added to an alkene, the solution becomes decolorized, indicating the presence of the double bond. This is because the alkene reacts with the bromine, converting it into a saturated compound.
Question 2: Reagent for Testing Aldehydes
What reagent is used to test for aldehydes?
Answer: Tollens’ reagent or Fehling’s solution
Explanation:
Aldehydes (organic compounds with the functional group –CHO) give a silver mirror with Tollens’ reagent or a brick-red precipitate with Fehling’s solution.
Question 3: Sweet-Smelling Compound with Ethanol and H₂SO₄
Which compound produces a sweet smell when mixed with ethanol and concentrated sulfuric acid?
Answer: Ester
Explanation:
Esters are known for their sweet, fruity aroma. The process is called esterification, and it occurs when ethanol reacts with a carboxylic acid in the presence of concentrated H₂SO₄.
Question 4: Reaction of Ethanol with Acidified Potassium Dichromate
What happens when ethanol is heated with acidified potassium dichromate (K₂Cr₂O₇)?
Answer: Ethanol is oxidized to ethanoic acid (CH₃COOH)
Explanation:
Acidified dichromate is a strong oxidizing agent. It changes the alcohol into a carboxylic acid (ethanoic acid), and the orange color of dichromate changes to green.
Question 5: Test for Proteins
What test is used to confirm the presence of protein?
Answer: Biuret Test
Explanation:
When Biuret reagent is added to a protein solution, it changes to a purple/violet color, confirming the presence of peptide bonds in proteins.
Question 6: Test for Fats and Oils
How do you test for fats and oils?
Answer: Use the grease spot test
Explanation:
Place a drop of the suspected fat or oil on a piece of paper. If the paper becomes translucent, it indicates the presence of fats or oils.
Question 7: Glucose and Benedict’s Solution
What color change occurs when glucose is added to Benedict’s solution and heated?
Answer: A brick-red precipitate is formed
Explanation:
Glucose is a reducing sugar. It reduces Benedict’s reagent from blue to a reddish or brick-red precipitate, confirming the presence of glucose.
Question 8: Test for Phenol
Which reagent confirms the presence of phenol?
Answer: Iron (III) chloride (FeCl₃)
Explanation:
Phenol reacts with Fe³⁺ to form a purple-colored solution, which is a clear indication of phenol in the sample.
Question 9: Starch Confirmation Test
What test is used to confirm the presence of starch?
Answer: Iodine solution
Explanation:
When iodine solution is added to starch, the solution turns blue-black, confirming starch’s presence.
Question 10: Acetic Acid + Sodium Carbonate Reaction
What happens when acetic acid (ethanoic acid) reacts with sodium carbonate?
Answer: A neutralization reaction occurs, producing:
- Sodium ethanoate (CH₃COONa)
- Carbon dioxide (CO₂)
- Water (H₂O)
Explanation:
This is a typical acid-carbonate reaction. Effervescence (bubbling) from CO₂ gas indicates a successful reaction.
Watch more educational videos and past questions: https://youtube.com/@allcbts
Final Takeaway: Why These Questions Matter
These 10 questions cover key areas tested in:
- WAEC Chemistry Paper 1 & 2
- NECO Chemistry Objective
- JAMB Chemistry UTME
- GCE and JUPEB Chemistry
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