Chemistry Exam Past Questions and Answers | JAMB, WAEC and NECO

Chemistry is the study of the substances that make up matter. It looks at their properties, how they react with each other, and how these reactions can create new substances.

• Question 2021: A substance Z reacts with NaOH to give salt and water only. When Z is treated with dilute HCl, a gas is evolved which gives a yellow suspension on passing into concentrated H₂SO₄. Substance Z is? Options:
  A) NaHS
  B) Na₂SO₃
  C) Na₂S
  D) NaHSO₃
  Show Answer
  The correct answer is A .
• Question 2022: 50 cm³ of carbon (II) oxide was exploded with 150 cm³ of air containing 20% oxygen by volume. Which of the reactants was in excess? Options:
  A) Carbon (II) oxide
  B) Carbon (IV) oxide
  C) Oxygen
  D) Nitrogen
  Show Answer
  The correct answer is C .
• Question 2023:

  A radioactive nucleus has a half-life of 20 years, starting with 100,000 particles, how many particles will be left exactly at the end of 40 years

  Options:
  A) 75,000 particles
  B) 35,000 particles
  C) 25,000 particles
  D) 50,000 particles
  Show Answer
  The correct answer is C .
• Question 2024: 2.0g of a monobasic acid was made up to 250 cm³ with distilled water. 25.00 cm³ of this solution required 20.00cm³ of 0.1 M NaOH solution for complete neutralization. The molar mass of the acid is? Options:
  A) 200 g
  B) 160 g
  C) 100 g
  D) 50 g
  Show Answer
  The correct answer is C .
• Question 2025: When cathode rays are deflected onto the electrode of an electrometer, the instrument becomes Options:
  A) negatively charged
  B) positvely charged
  C) neutral
  D) bipolar
  Show Answer
  The correct answer is A .
• Question 2026:

  Oxygen is absent in?

  Options:
  A) Kerosene
  B) Soil
  C) Glass
  D) Cement
  Show Answer
  The correct answer is A .
• Question 2027: Which of the following methods may be used to prepare trioxonitrate (V) acid (nitric acid) in the laboratory? Options:
  A) Heating ammonia gas with tetraoxosulphate (VI) acid
  B) Heating ammonium trioxonitrate (V) with tetraoxosulphate (VI) acid
  C) Heating sodium trioxonitrate (V) with tetraoxosulphate (VI) acid
  D) Heating potassium trioxonitrate (V) with calcium hydroxide
  E) Heating a mixture of ammonia gas and oxygen.
  Show Answer
  The correct answer is C .
• Question 2028: Alloys are best prepared by? Options:
  A) high temperature weilding of the metals
  B) electrolysis using the major metallic component as cathode
  C) reducing a mixture of the oxies of the elements
  D) cooling a molten mixture of the necessary elements
  Show Answer
  The correct answer is D .
• Question 2029:

  An example of a polysaccharide is?

  Options:
  A) Dextrose
  B) Mannose
  C) Glucose
  D) Starch
  Show Answer
  The correct answer is D .
• Question 2030:

  The solubility of Na₃AsO₄(H₂O)₁₂ is 38.9g per 100g H₂O. What is the mass percentage of Na₃AsO₄ in the saturated solution?

  (As = 75, Na = 23, O = 16, H = 1)

  Options:
  A) 87.27%
  B) 38.9%
  C) 19.1%
  D) 13.7%
  Show Answer
  The correct answer is C .