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 111:

  CO_(g) + H₂O_(g) → CO_2(g) + H_2(g)

  From the reaction above, calculate the standard enthalpies of formation of CO_2(g), H₂O_(g) and CO_(g) in kJ mol^-1 are -394, -242, and -110 respectively.

  Options:
  A) -262 kJ mol^-1
  B) -42 kJ mol^-1
  C) +42 kJ mol^-1
  D) +262 kJ mol^-1
  Show Answer
  The correct answer is B .
• Question 112: CO_g + H₂O_g $\to$ _2g + H_2g $\mathrm{\Delta }$H = -4100J. Which of the following factors favour the formation of hydrogen in the above reaction? i. high pressure. ii. low pressure iii. high temperature iv. use of excess steam Options:
  A) i, iii and iv
  B) iii only
  C) ii, iii and i
  D) iv only
  Show Answer
  The correct answer is D .
• Question 113: Alkanals can be differentiated from alkanones by reaction with? Options:
  A) 2,4-dinitrophenylhydrazine
  B) hydrogen cyanide
  C) sodium hydrogen sulphite
  D) Tollen's reagent
  Show Answer
  The correct answer is D .
• Question 114: An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. The empirical formula of the compound is Options:
  A) C₈H₂₂O₃
  B) C₆H₁₀O₃
  C) C₁₂H₁₂O
  D) C₆H₁₂O
  E) C₃H₆O
  Show Answer
  The correct answer is D .
• Question 115: In which of the following reactions does reduction takes place Options:
  A) Fe²⁺ - e^- → Fe³⁺
  B) 2O^2- →O₂ + 4e^-
  C) Cr – 2e^- → Cr²⁺
  D) 2H⁺ + 2e^- → H₂
  Show Answer
  The correct answer is D .
• Question 116: The process by which atoms are rearranged into different molecular structure in the petroleum refining process is referred to as Options:
  A) catalytic cracking
  B) hydrocracking
  C) polymerization
  D) reforming
  Show Answer
  The correct answer is D .
• Question 117: Magnesium ribbon was added to each of the following aqueous solution in turn: H₂SO₄, AgNO₃, HNO₃, HCl, NH₃, HCl, NH₃. In which case does the magnesium become covered with a dark precipitate? Options:
  A) H₂SO₄
  B) AgNO₃
  C) HNO₃
  D) NH₃
  E) HCl
  Show Answer
  The correct answer is B .
• Question 118:

  If the quantity of oxygen occupying 2.76L container at a pressure of 0.825 atm and 300k is reduced by one-half, what is the pressure exerted by the remaining gas?

  Options:
  A) 1.650atm
  B) 0.825atm
  C) 0.413atm
  D) 0.275atm
  Show Answer
  The correct answer is A .
• Question 119: 35 cm³ of hydrogen was sparked with 12 cm³ of oxygen at 110°C and 760mm Hg to produce steam. What percentage of the total volume of gas left after the reaction is hydrogen? Options:
  A) 11%
  B) 31%
  C) 35%
  D) 69%
  Show Answer
  The correct answer is B .
• Question 120: Mineral acids are usually added to commercial hydrogen peroxide to Options:
  A) oxidize it
  B) decompose it
  C) minimize its decomposition
  D) reduce it to water and oxygen
  Show Answer
  The correct answer is C .