Welcome to the second session of the Chemistry Practical tutorial by AllCBTs!
In this guide, we tackle Questions 31 to 40 from the NECO Chemistry Practical past papers — breaking them down clearly with explanations that help you understand not just the what, but the why behind each correct option.
You can watch the full class in the video below:
Question 31: Confirming the Presence of Nitrate Ion
Question:
Which of the following tests confirms the presence of the nitrate ion (NO₃⁻)?
Options:
A. Add sodium hydroxide and warm
B. Add iron(II) tetraoxosulphate(VI) and concentrated H₂SO₄
C. Add barium chloride solution
D. Add silver nitrate solution
Correct Answer: B
Explanation:
This is known as the brown ring test. Adding Fe²⁺ solution followed by concentrated H₂SO₄ forms a brown ring, indicating the presence of nitrate ions.
Question 32: Phenolphthalein in a Basic Solution
Question:
What color does phenolphthalein turn in a basic solution?
Options:
A. Pink
B. Red
C. Yellow
D. Colorless
Correct Answer: A. Pink
Explanation:
Phenolphthalein is colorless in acidic solutions but turns pink in basic (alkaline) environments.
Question 33: Identifying a Colorless Gas with Pungent Smell
Question:
A colorless gas with a pungent smell that turns red litmus paper blue is:
Options:
A. HCl
B. Sulphur dioxide
C. Ammonia
D. Carbon(IV) oxide
Correct Answer: C. Ammonia
Explanation:
Ammonia is a basic gas, so it turns red litmus paper blue. It’s also pungent and colorless.
Question 34: Metal Reaction with Cold Water and Steam
Question:
Which metal reacts slowly with cold water but faster with steam?
Options:
A. Sodium
B. Calcium
C. Zinc
D. Potassium
Correct Answer: C. Zinc
Explanation:
Zinc reacts slowly with cold water but much faster with steam. Sodium and potassium react violently even with cold water.
Question 35: Factor That Doesn’t Affect Reaction Rate
Question:
Which of these does not affect the rate of a chemical reaction?
Options:
A. Catalyst
B. Surface area
C. Color of reactants
D. Temperature
Correct Answer: C. Color of reactants
Explanation:
Color is unrelated to the rate of reaction. Catalysts, temperature, and surface area all affect how fast a reaction proceeds.
Question 36: Test for Sulphate Ions (SO₄²⁻)
Question:
Which test confirms the presence of sulphate ions?
Options:
A. Add barium chloride to form white precipitate
B. Add HCl to give gas
C. Add silver nitrate to form precipitate
D. Add sodium hydroxide to give brown precipitate
Correct Answer: A
Explanation:
Adding barium chloride to a solution containing sulphate ions gives a white precipitate of barium sulphate — a standard test for sulphates.
Question 37: Blue-Green Flame in Flame Test
Question:
Which ion gives a blue-green flame during a flame test?
Options:
A. Sodium
B. Copper(II)
C. Potassium
D. Calcium
Correct Answer: B. Copper(II)
Explanation:
Copper(II) ions produce a blue-green flame, which helps in identifying them during flame tests.
Question 38: Test for Iron(III) Ions
Question:
The presence of Iron(III) ions is confirmed by:
Options:
A. Reddish-brown precipitate with sodium hydroxide
B. White precipitate with ammonium solution
C. Blue precipitate with sodium hydroxide
D. Green solution
Correct Answer: A
Explanation:
Fe³⁺ (Iron(III)) reacts with sodium hydroxide to give a reddish-brown precipitate, confirming its presence.
Question 39: Gas That Gives a Pop Sound with Flame
Question:
Which gas gives a pop sound when tested with a burning splint?
Options:
A. Hydrogen
B. Carbon dioxide
C. Oxygen
D. Ammonia
Correct Answer: A. Hydrogen
Explanation:
Hydrogen gas gives a characteristic ‘pop’ sound when ignited — a classic confirmatory test.
Watch more educational videos and past questions: https://youtube.com/@allcbts
Final Tips for NECO Chemistry Practical 2025
- Memorize confirmatory tests for ions like nitrate, sulphate, iron(III), and ammonia.
- Understand the color changes and precipitates expected in common reactions.
- Practice flame tests and solubility trends to identify metal ions confidently.
- Use keywords like brown ring test, blue-green flame, and precipitate formation during your exams.
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