National Examinations Board Grade 12 Chemistry — Model Question 2079 (2023)

National Examinations Board · Chemistry (Grade 12) · 2079 (2023) BS · Model Question — 22 questions — a free old question paper on Goodone.club’s exam-paper archive.

  1. Identify the equivalent weight of K₂Cr₂O₇ in the following reaction (Cr = 52, K = 39): K₂Cr₂O₇ + 3H₂SO₄ + 5(COOH)₂ → K₂SO₄ + Cr₂(SO₄)₃ + 10CO₂ + 8H₂O (A) 49 (B) 294 (C) 98 (D) 108 [1 marks]
  2. The addition of a solution of the required concentration in a reaction mixture yields profitable products and saves reactants. (a) A solution of HCl is labelled 2 M. Clarify its meaning. [1] (b) In which aspects is molarity different from molality? [1] (c) List the significance of the normality factor in the preparation of a standard solution. [1] (d) Liquor ammonia kept in a corner of your chemistry lab is 25% (w/w) NH₃ and its specific gravity is 0.91. Find the molarity of liquor ammonia. [2] [5 marks]
  3. Ostwald's dilution law is α = √(Ka/C). (a) Derive it. [3] (b) What information can you obtain from this expression? [2] (c) Will strong electrolytes obey this expression? Why? [1] (d) 0.1 M ethanoic acid is 1.34% ionized. Find its dissociation constant. [2] OR (a) Hess's law is applied to calculate different types of enthalpy of reaction. (i) Illustrate Hess's law of constant heat summation. (ii) Standard enthalpies of combustion of C(s), H₂(g) and C₂H₂(g) are −394, −286 and −1300 kJ mol⁻¹ respectively; calculate the enthalpy of formation of acetylene. [2+4] (b) Draw the energy-profile diagram... [8 marks]
  4. In a solution that is at equilibrium, what happens to the concentration of H⁺ ions if the concentration of OH⁻ ions is increased? (A) The concentration of H⁺ ions increases (B) The concentration of H⁺ ions decreases (C) The concentration of H⁺ ions stays the same (D) It depends on the initial concentration of H⁺ ions [1 marks]
  5. (a) Write the differences between rate of reaction and rate constant. [2] (b) For the reaction 2A + B → product, the following data were obtained: Exp 1: [A]=0.50, [B]=0.50, rate=1.6×10⁻⁴; Exp 2: [A]=0.50, [B]=1.00, rate=3.2×10⁻⁴; Exp 3: [A]=1.00, [B]=1.00, rate=3.2×10⁻⁴ (mol L⁻¹ s⁻¹). Find (i) order with respect to A and B [1]; (ii) the rate constant [1]; (iii) the rate when [A]=0.5 M and [B]=0.4 M [1]. OR Four metals A, B, C and D react as follows: B displaces only A from solution; only D and C displace hydrogen from 1 M HCl; none of the metals displaces C from solution. (i) Make the activit... [5 marks]
  6. An organic compound C₂H₄O₂ has two functional isomers A and B. Isomer A turns blue litmus red and B has a fruity smell. (a) Give the reaction for the formation of A using Grignard's reagent. [1] (b) Convert isomer A into isomer B. [2] (c) Write a suitable test reaction to distinguish A from methanoic acid. [1] (d) Arrange the following in decreasing order of acidic strength and give reasons: CH₃COOH, ClCH₂COOH, FCH₂COOH, C₆H₅COOH. [2] (e) Identify A and B of the given reactions. [2] OR Amines are derivatives of ammonia in which one or more hydrogen atoms are replaced by alkyl or aryl groups. (... [8 marks]
  7. Assuming the rate of a reaction is doubled for every 10 °C rise in temperature, how many times does the rate increase as the temperature rises from 10 °C to 100 °C? (A) 112 times (B) 400 times (C) 512 times (D) 614 times [1 marks]
  8. An ammonia solution is added to the sulphate of a coinage metal A; a blue precipitate B appears which dissolves in excess reagent to form a deep-blue solution C. (a) Identify A, B and C with the sequence of chemical reactions. [3] (b) Predict the electronic configuration of metal A. [1] (c) Select a suitable method for the purification of metal A. [1] [5 marks]
  9. (a) How are cements classified on the basis of hardening and setting behaviour? [2] (b) Differentiate between: (i) paper and pulp [2]; (ii) artificial and natural radioactivity [2]; (iii) addition and condensation polymers [2]. [8 marks]
  10. For the given reactions: (i) C + O₂ → CO₂, ΔH = −x kJ mol⁻¹; (ii) 2CO + O₂ → 2CO₂, ΔH = −y kJ mol⁻¹. The enthalpy of formation of CO becomes (A) 2y − x (B) 2x − y (C) (y − 2x)/2 (D) (x − 2y)/2 [1 marks]
  11. What is meant by d–d electron transitions? List the characteristics of transition metals. [1+4] [5 marks]
  12. What product would be obtained if red-hot copper wire reacts with steam? (A) CuO (B) Cu₂O (C) Cu₂O₂ (D) CuO₂ [1 marks]
  13. Write the structural formula and IUPAC name of the tertiary alcohol with formula C₄H₁₀O. How would you apply Victor Meyer's method to distinguish 1-propanol and 2-propanol? Explain. [1+4] [5 marks]
  14. For which manufacturing process is a Bessemer converter used? (A) Pig iron (B) Steel (C) Wrought iron (D) Cast iron [1 marks]
  15. An organic compound X reacts with methyl magnesium bromide followed by acidic hydrolysis to yield compound Y. Y on oxidation with acidified KMnO₄ yields Z. All three give a positive iodoform test. (a) Predict X, Y and Z with the sequence of reactions and give their IUPAC names. [3] (b) Give the product of reacting Z with dilute NaOH. [2] OR An organic compound X, when heated with acetone, gives hypnotic and nervous-sedative drugs and forms carbonyl chloride when exposed to air. (a) Predict X [1]. (b) Write the reactions for the formation of X from ethanol [2]. (c) Predict the new compound form... [5 marks]
  16. When sodium phenoxide reacts with methyl bromide it gives (A) Cresol (B) Toluene (C) Benzene (D) Anisole [1 marks]
  17. (a) The nitro group in nitrobenzene is a meta-directing group towards electrophilic substitution reactions — why? How does nitrobenzene react with (i) Zn/NH₄Cl and (ii) LiAlH₄? [2+2] (b) What are the isomers of formula C₂H₇N? [1] [5 marks]
  18. Identify X in the following reaction: nitrobenzene (with two NO₂ groups) → X → product with NH₂ group. (A) Na₂S (B) Sn/HCl (C) LiAlH₄ (D) Na/H₂ [1 marks]
  19. Give an example of each of the following reactions: (a) Reimer–Tiemann reaction; (b) Perkin condensation reaction; (c) Williamson ether synthesis; (d) Cannizzaro reaction; (e) Sandmeyer reaction. [1×5] [5 marks]
  20. Which of the following reagents can be used to distinguish between a phenol and a carboxylic acid? (A) KOH (B) Na (C) NaOH (D) NaHCO₃ [1 marks]
  21. The colourless, sweet-smelling liquid compound A, which on exposure to air forms poisonous phosgene and also reacts with acetone to give a sleep-inducing drug. Predict the product when compound A is reduced in a neutral medium. (A) Methylene chloride (B) Methane (C) Ethyne (D) Ethane [1 marks]
  22. An oxygen-containing organic compound upon oxidation forms a carboxylic acid as the major organic product with its molecular mass higher by 14 units. Identify the organic compound. (A) A primary alcohol (B) An aldehyde (C) A ketone (D) A secondary alcohol [1 marks]