Chemistry Examinations 2023

Ammonia is produced by Haber-Basch process according to the following equation: N2(g) + 3H2(g) 2NH3(g) ∆H=-92KJmol-1 Indicate and explain what will happen to the position of equilibrium if: (a) Pressure is decreased (2 marks) (b) Temperature is decreased (2 marks)

(a).What is a buffer solution? (1 mark) (b). calculate the number of moles of CH3COOH and CH3COONa that are necessary to prepare a buffer solution with pH=4.47 and pKa (CH3COOH)=4.75 (3 marks)

(a).Silver chloride is sparingly soluble in water. Write: (i). equation for the solubility of silver chloride in water. (1 mark) (ii). The expression for the solubility product, Ksp of silver chloride. (1 mark) (b). The solubility product Ksp, of calcium chloride is 5.3x10-2 mol3l-3 at 25oC. Calculate the concentration of the following ions in a saturated solution of calcium chloride. (i). Calcium ions (1 mark) (ii). Chloride ions (1 mark)

(a) Calculate the pH of the solution after 15cm3 of 0.1M sodium hydroxide have been added to 25cm3 of 0.1M ethanoic acid. (PKa =4.76). (3 marks) (b). How many times times more hydrogen ions are in an acid of pH =1 than an acid of pH=5? (2 marks)

A buffer solution contains 0.2 moldm-3 propanoic acid and 0.5moldm-3 sodium propanoate. (a) What is meant by the term buffer solution? (1 mark) (b) Calculate the pH of the buffer solution. (2 marks) (ka of propanoic acid = 1.35 x 10-5) (c) Using relevant equations, explain how the buffer solution reacts when a small amount of hydrochloric acid is added. (1 mark)

When 100cm3 of aqueous solution containing 30g of ethanoic acid was shaken with 50cm3 of butan-1-ol. 12g of ethanoic acid remained in the aqueous layer. (a) Calculate the distribution coefficient of ethanoic acid between water and butan-1-ol. (2 marks) (b) The aqueous solution of ethanoic acid was shaken twice with 25cm3 of butan-1-ol. Calculate the mass of ethanoic acid extracted.(3 marks)

(a).State two factors that affect solubility. (2 marks) (b).State Raoult’s law. (2 marks) (c).A solution containing 0.142g of naphthalene in 20.25g of benzene caused a lowering of freezing point of 0.284oC. Calculate the molar mass of naphthalene. (Cryoscopic constant Kf of benzene is 5.12oCmol-1Kg-1) (3 marks)

(a).The dissociation constant constant Ka of a dibasic acid is 4.39 x 10-5 moldm-3 at 25oC. Calculate the degree of dissociation of a 0.01M solution of the acid. (1 mark) (b). Write: (i). an equation for the ionization methylamine (CH3NH2) in water. (1 mark) (ii). the expression for the dissociation constant Kb, for methylamine. (1 mark) (iii). the hydrogen ion concentration of a 1M methylamine solution is 2.5 x 10-13 moldm-3. Calculate Kb for methylamine. (1 mark)

(a). Define an acid and a base according to bronsted theory. (2 marks) (b). State the conjugate acid and base in these reaction. (2 marks) (i). S2+(aq) + H3O+ HS-(aq) + H2O (aq) (ii). N2H4(aq) + H2O(l) N2H5+(aq) + OH-(aq)

(i) Calculate the pH of a 0.1M aqueous solution of sodium methanoate at 25oC. (ionic product of water is 1x10-14 moldm-3 at 25oC) (3 marks) (ii) The pH of 0.12M solution of ethanoic acid, CH3COOH, is 2.60. Calculate the Ka of the acid. (2 marks) (b). Explain what would happen to the pH of a solution containing sodium methanoate and methanoic acid, if to it was added a small amount of (i) hydrochloric acid (2 marks) (ii) sodium hydroxide (2 marks) (c). State two applications of a buffer. (1 mark)