Characteristics 1. What is the meaning of "d-block element"? AL CHEMISTRY d-block ELEMENTS Exercises from Past Exam Questions 2. Illustrate, with examples using nickel, two characteristic properties of transition metals. 3. (a) What do you understand by the following terms? (i) complex ion (ii) stability constant In each case, illustrate your answer with an example involving copper(ii). [91II 6(a)(i)] [94II 5(a)(i)] (1 mark) [90I 3(d)] (2 marks) (b) State THREE characteristic properties of d-block elements, apart from complex ion formation. In each case, illustrate your answer with an example involving copper or vanadium. [96II 6(b)(c)] (8 marks) 4. Explain why a transition element usually forms compounds in a range of oxidation states. [88II 5(a)] (3 marks) 5. State two reasons why transition metal ions readily form complexes whereas Group I metal ions do not. [92II 4(a)(vi)] [94I 2(b)(i)] (2 marks) 6. Explain, in terms of electronic arrangement, why most transition metal ions are coloured. 7. Explain why most transition metals have catalytic properties. Variable Oxidation States [93I 2(b)] (2 marks) [92I 3(h)] [94II 5(a)(iv)] (2 marks) 8. (i) Using the 'electrons-in-boxes' representation, give the electronic structure outside the argon core of Cu and Cr 3+. (ii) Which of the two ions, copper(i) or copper(ii), has the more stable electronic structure? Give an explanation. (iii) Why is the copper(i) ion unstable in aqueous solution? [92II 4(a)(i-iii)] (4 marks) 9. (i) Using the electrons-in-boxes representation, write the electronic structure outside the argon core for Mn 2+ and Fe 2+ respectively. (ii) Explain briefly why Fe 2+ ions are easily oxidized to Fe 3+ ions, but Mn 2+ ions are not readily oxidized to Mn 3+ ions. [94II 5(a)(ii-iii)] (5 marks) 10. In acidic solutions, VO + 2 (aq) can be reduced by sulphur dioxide to give VO 2+ (aq). Write a balanced equation for the reaction. [96II 6(e)] (2 marks) 11. Why do V 4+ ions react to give VO 2+ ions in aqueous solution? State the reagents you would employ to obtain (i) vanadium(iv), and (ii) vanadium(ii) from vanadium(v) in an acidic solution of ammonium metavanadate, NH 4 VO 3, and give the colours of the products. [91II 6(a) (iii-iv)] (5 marks) 12. (i) Draw the structures of the chromate(vi) and dichromate(vi) ions. (ii) Write an equation showing the action of aqueous acid on the chromate(vi) ion. (iii) Compare the action of hydrogen peroxide on the dichromate(vi) ion and on the chromium(iii) ion. [92II 4(b)] (5 marks) 13. (i) Show the electronic configuration of a ground state Cr 2+ ion by electron-in-boxes representation. (ii) What is the highest possible oxidation state of chromium? (iii) Give a chromium compound in which chromium is in its highest oxidation state. [95I 2(f)] (3 marks) 14. The effluent from an electroplating factory contains toxic Cr 2 O 7 2- (aq). Suggest, with balanced equations, how all chromiumcontaining species can be removed from the effluent before discharge. [97I 3(c)] (4 marks) 1
15. (i) Draw the 3-D structure of the manganate(vii) ion. (ii) Manganate(VI) ions readily undergo disproportionation in aqueous solutions, except under very basic conditions. Write a balanced equation for this disproportionation, and give the oxidation state of manganese in the reaction product(s). [95I 2(c)] (3 marks) Complex Compounds 16. The analysis of a compound Co(NH 3 ) x Cl y yielded the following composition by mass : Co, 25.59 % ; NH 3, 29.00 % ; Cl, 45.41 %. (i) Calculate the values of x and y. (ii) Draw and name all possible structures for this compound. [Ans: x = 4; y = 3] (7 marks) 17. Chromium(III) chloride crystallizes from its aqueous solution to form three structural isomers : [Cr(H 2 O) 6 ] 3+ 3Cl - ; [Cr(H 2 O) 5 Cl] 2+ 2Cl -. H 2 O ; and [Cr(H 2 O) 4 Cl 2 ] + Cl -. 2H 2 O. Outline a chemical method which can be used to distinguish the three isomers from one another. [88I 2(g)] (3 marks) 18. An aqueous solution contained 0.40g of a complex salt Cr(NH 3 ) 5 Cl 3. The free chloride ions present in the solution required 21.90 cm 3 of 0.150 M silver nitrate(v) solution for complete precipitation. Deduce the structural formula of the complex ion present in the salt. (Ans: [Cr(NH 3 ) 5 Cl] 2+ ) [97I 7(b)] (4 marks) 19. There are three compounds of chromium with the same formula [Cr(en) 2 Cl 2 ] + Cl - ; where en is ethane-1,2-diamine, H 2 NCH 2 CH 2 NH 2. Draw a three-dimensional structure for one of these three compounds, and give its systematic name. [93I 2(b)(iii)] (2 marks) 20. Explain why the stability constant of the copper(ii)-edta complex is much greater than that of the copper(ii)-nh 3 complex. [92II 4(a)(ix)] (2 marks) Coloured Compounds 21. Explain, using balanced equations, the following observations : Upon addition of aqueous ammonia to a pink aqueous solution of cobalt(ii) nitrate, a blue precipitate is formed, which redissolves in excess ammonia solution to give a yellow-brown solution. Upon exposure to air, this yellow-brown solution gradually turns red. [89II 5(a)(i)] (6 marks) 22. Account for the following : The addition of 2M NaOH to an aqueous solution of Fe 3+ ions gives a brown precipitate, whereas the addition of 2M NaOH to an aqueous solution of Fe 3+ ions in the presence of excess CN - ions gives no precipitate. [94II 5(b)(iii)] (6 marks) 23. Write equations for the reactions described below : The addition of an aqueous solution of KSCN to a solution containing Fe(III) ions gives a complex with a deep red colour. The deep red colour fades when excess NaF solution is added. On the addition of dilute alkali to the resulting solution, a brown precipitate forms. [93I 2(b)(iv)] (3 marks) 24. Give the outer valence shell electronic configuration of each of the following ions : Ti 3+, V 4+, Mn 3+, Sc 3+, and Cu +. Which of the above hydrated ions would you expect to be colourless? Give reasons for your answer. [88II 5(b)] 25. In aqueous solutions, TiO 2+ is colourless. It can be reduced to give a violet solution containing [Ti(H 2 O) 6 ] 3+. (i) Draw the three-dimensional structure of [Ti(H 2 O) 6 ] 3+. (ii) Explain the colour change from TiO 2+ to [Ti(H 2 O) 6 ] 3+. [95II 6(c)(i-ii)] 26. Account for each of the following : (i) Cobalt(II) chloride can be used to test for the presence of water. (6 marks) (4 marks) [01I 3(c)] (2 marks) 2