National Examinations Board Grade 12 Chemistry — Grade Increment (Supplementary) 2080 (2023) (Set A)

National Examinations Board · Chemistry (Grade 12) · 2080 (2023) BS · Grade Increment (Supplementary) Examination — 22 questions — a free old question paper on Goodone.club’s exam-paper archive.

  1. Give an example of each of the following reactions: (i) Coupling reaction; (ii) Hydroboration oxidation; (iii) Clemmensen's reduction; (iv) Fehling test; (v) Carbonylation reaction. [1×5] [5 marks]
  2. Phenol is heated with CHCl₃ and aq. KOH to produce salicylaldehyde. This reaction is called (A) Friedel-Crafts reaction (B) Rosenmund's reaction (C) Reimer-Tiemann reaction (D) Carbylamine reaction [1 marks]
  3. Normality factor and titration error are important in analytical chemistry for determining the variation of the observed result for the same experiment. (i) Distinguish between normality factor and titration error. [2] (ii) A chemistry lab-boy weighed 1.31 g of Na₂CO₃ to prepare 250 ml of its decinormal solution. (a) Calculate the actual strength of the solution indicating the normality factor. (b) Find the volume of water required to be evaporated to make it exactly normal solution. (c) Calculate the mass of oxalic acid crystals required to neutralise the solution completely. [2+1+2] (iii) Ho... [8 marks]
  4. Which of the following reactions is used to distinguish a carboxylic acid from other organic compounds? (A) reaction with sodium metal (B) reaction with bicarbonate (C) reaction with magnesium metal (D) reaction with chlorine [1 marks]
  5. An organic compound A (molecular formula C₄H₈O₂) undergoes acid hydrolysis to produce a carboxylic acid B and an alcohol C. When B is reduced with LiAlH₄, the alcohol C is produced. (i) Draw the molecular structures of A, B and C with proper reactions. (ii) What products would you expect when A is reduced with LiAlH₄? [4+1] [5 marks]
  6. An alcohol A of molecular formula C₃H₈O undergoes Victor Meyer's reaction to give a blue colour at the end of the reaction when KOH solution is added. (i) Draw the structural formula and IUPAC name of A. [1] (ii) Give the complete chemical reaction for the Victor Meyer's test of A. [2] (iii) Starting from CH₃MgBr, how would you prepare compound A? [2] (iv) What happens when A is oxidised? [1] (v) Convert A into propene. [2] OR (i) Give proper chemical reactions for the preparation of benzaldehyde from (a) benzyl chloride (b) toluene. [2] (ii) Convert benzaldehyde into (a) toluene (b) cinnamic... [8 marks]
  7. Silver gets tarnished in air due to reaction with (A) O₂ (B) CO₂ (C) H₂O (D) H₂S [1 marks]
  8. You are given a bottle containing a mixture of R-NH₂, R₂NH and R₃N. How would you apply Hoffmann's method to separate each compound in a pure state? [5] [5 marks]
  9. (The full text of Question 22 — the final 8-mark long-answer question of this supplementary paper — was not legible in the available source scan; the scanned copy ends before it. Refer to the original NEB paper for this question.) [8 marks]
  10. Lithopone is a mixture of (A) ZnSO₄, BaSO₄ (B) ZnS, BaSO₄ (C) ZnCO₃, BaCO₃ (D) ZnS, Na₂SO₄ [1 marks]
  11. Describe the rusting theory of iron. Name the process of preventing iron from rusting. [4+1] [5 marks]
  12. The correct decreasing order of acidic strength of a 0.1 M solution of the following acids is (A) F₂CHCOOH > FCH₂COOH > ClCH₂COOH > CH₃COOH (B) FCH₂COOH > F₂CHCOOH > ClCH₂COOH > CH₃COOH (C) ClCH₂COOH > FCH₂COOH > F₂CHCOOH > CH₃COOH (D) CH₃COOH > ClCH₂COOH > FCH₂COOH > F₂CHCOOH [1 marks]
  13. (i) What is meant by transition metal? [1] (ii) Justify, giving proper reasons: (a) Transition metals mostly form coloured compounds. (b) Zinc is regarded as a non-typical transition metal. [1+1] (iii) Draw the splitting of d-orbitals in an octahedral field showing the eg set and t2g set. [2] [5 marks]
  14. Another name for grain alcohol is (A) wood alcohol (B) methyl alcohol (C) ethyl alcohol (D) propyl alcohol [1 marks]
  15. An electrochemical cell is connected using an aluminium (Al) electrode and a silver (Ag) electrode whose standard electrode potentials are −1.67 V and +0.80 V respectively. (i) Write the cell notation indicating anode and cathode. [2] (ii) Write the oxidation-half and reduction-half reactions occurring in the cell. [2] (iii) Calculate the e.m.f. of the cell. [1] [5 marks]
  16. Primary and secondary amines are distinguished by (A) Br₂/KOH (B) HClO (C) HNO₂ (D) NH₃ [1 marks]
  17. Enthalpies of formation of H₂O(l), CO₂(g) and C₂H₅OH(l) are −286, −394 and −2010 kJ/mol respectively. (i) What is meant by enthalpy of formation? [1] (ii) Write balanced thermochemical reactions for each of the above processes. [1] (iii) Calculate the enthalpy of combustion of C₂H₅OH(l) from the above data. [3] OR (i) Deduce the relation between pH and pOH at 25°C. [2] (ii) The solubility product of AgCl is 1.8×10⁻¹⁰. What mass of AgCl (molecular mass = 143.5) will be precipitated if 0.2 mole of HCl solution is added to the saturated solution of AgCl? [3] [5 marks]
  18. The specific rate constant of a 1st-order reaction depends on (A) concentration of reactant (B) temperature (C) time (D) concentration of product [1 marks]
  19. Represent a regular sequence of reactions of the following sets of organic compounds using suitable catalysts, reagents or conditions: CH₃CH₂CH₂Cl, CH₃CH₂NH₂, CH₃CH₂CH₂OH, CH₃CH₂COOH, CH₃CH₂CONH₂. OR Formic acid is the first member of the carboxylic acids and is naturally found in ant stings and bee venom. (i) Draw the molecular formula of formic acid and write its IUPAC name. [1] (ii) How is formic acid prepared from (a) chloroform (b) ethane-1,2-dioic acid? [1+1] (iii) Distinguish formic acid from acetic acid with a chemical reaction. [1] (iv) Why is formic acid more acidic than acetic acid?... [5 marks]
  20. Calculate the number of H⁺ ions present in 1 ml of a solution whose pH = 13. (A) 6.02×10⁷ (B) 6.02×10⁸ (C) 6.02×10⁹ (D) 6.02×10¹⁰ [1 marks]
  21. What will be the value of ΔS for the conversion of ice into water when they are in equilibrium? (Δh = 6 kJ/mol) (A) 0.022 kJ K⁻¹mol⁻¹ (B) 0.025 kJ K⁻¹mol⁻¹ (C) 0.027 kJ K⁻¹mol⁻¹ (D) 0.029 kJ K⁻¹mol⁻¹ [1 marks]
  22. Find the volume of water to be added to 20 ml of 2N HCl to make it exactly decinormal. (A) 375 ml (B) 380 ml (C) 385 ml (D) 390 ml [1 marks]