(b) II I III (d) I III II. Higher the electronegativity of the atom attached with oxygen greater the acidity. So order is III II I (c)

Transcription

1 Chemistry: Concepts of Acids and Bases-1 Solved Problems bjective Problem 1: The following acids have been arranged in order of increasing acid strength. Identify the correct order. Cl (I) Br (II) I (III) (a) I II III (b) II I III (c) III II I (d) I III II igher the electronegativity of the atom attached with oxygen greater the acidity. So order is III II I (c) Problem : Among the following compounds, the strongest acid is (a) C C (b) C66 (c) C6 (d) C ydrogen atom attached with oxygen is maximum acidic. (d) Problem : The conjugate acid of P is (a) P (b) P (c) P (d) P Conjugate acid and base differs by one proton hence the conjugate acid of P is P (b) Problem : The anhydride of Cl is (a) Cl (b) Cl (c) Cl7 (d) None Cl has +7 oxidation state in Cl7 and Cl Anhydride is Cl7 (c) Problem 5: The conjugate acid of azide ion is (a) N (b) N (c) N (d) N N + + N (b) Problem 6: P is.. acid (a) Monobasic (b) Dibasic

2 Chemistry: Concepts of Acids and Bases- (c) Tribasic P (d) None Thus two hydrogens are attached with oxygen, therefore P is dibasic acid (b) Problem 7: Which salt undergoes hydrolysis (a) KCl (b) NaN (c) CaS (d) CN Salts of strong acids and strong bases do not hydrolyse. Thus only CN is hydrolysed (d) Problem 8: In the following compounds, the order of acidity is N C N (I) (II) (III) (IV) (a) III > IV > I > II (c) II > I > III > IV (b) I > IV > III > I (d) IV > III > I > II +I effect decreases acidity, I and R effect increases acidity. N group cannot exert R effect from the metal position. (d) Problem 9: Which of the following species is an acid and also a conjugate base of another acid (a) S (b) S (c) (d) + S can donate a proton also can accept a proton. (a) Problem 10: Among the following which is the least basic (a) F (b) I (c) Cl (d) Br I is the strongest acid among the hydro acids of halogen, so I is least acid. Problem 11: Which of the following species cannot be a Bronsted base? (a) (b) C (c) C (d) P. (b)

3 Chemistry: Concepts of Acids and Bases- Problem 1: In Mond s process, C(g) is passed over Ni(s) when volatile complex Ni( C ) escapes. Ni(s) C(g) Ni(C) (g) In this reaction, which one is correct. (a) Ni(s) is a Lewis base and C(g) is a Lewis acid (b) Ni(s) is a Lewis acid and C(g) is a Lewis base (c) Ni(s) as well as C(g) behaves as amphoteric (d) It is not Lewis acid-base reaction. (b) Problem 1: The compound Cl behaves as. in the reaction Cl + F + Cl + F (a) Strong acid (b) Strong base (c) Weak acid (d) Weak base Cl is accepting proton in F medium and acts as weak base. (d) Problem 1: Which of the following statements is true for a 0.1 M solution of a weak acid A? (a) the p is 1.00 (b) the p is less than 1 (c) [ ] [A ] (d) [ ] [A ]. (c) Problem 15: The anhydride of P is (a) P5 (c) P (b) P (d) None P has +5 oxidation numbers in P5 and P (a) Problem 16: The conjugate base of hydrazoic acid is (a) N (b) N (c) N (d) N N (c) N Problem 17: Strongest conjugate base is: (a) C (b) C C

4 Chemistry: Concepts of Acids and Bases- (c) C N (d) (d) Problem 18: Which of the following orders regarding acid strength is correct? (a) C < CC < PhC (b) C > PhC > CC (c) C > CC > PhC (d) CC > C > PhC (b) Problem 19: In the following compounds, the correct order of basicity is N N N N (I) (II) (III) (IV) (a) IV > I > III > II (c) II > I > III > IV (b) III > I > IV > II (d) I > III > II > IV (d) Problem 0: Arrange the following ions in increasing order of acidity. [Na ()6] +, [Al ()6] +,[Mn ()6] +, [Ni ()6] + (I) (II) (III) (IV) (a) I < II < III < IV (b) I < III < IV < II (c) I < III < II < IV (d) II < IV < III < II (b) Subjective Problem 1: Why sulphuric acid is stronger than sulphurous acid? Subphuric acid is stronger than sulphurous since the sulphur atom in sulphuric acid has more coordinated oxygen atoms. S S Sulphurous acid Sulphuric acid Problem : Explain

5 Chemistry: Concepts of Acids and Bases-5 F is a strong base Problem : Problem : Problem 5: Problem 6: Problem 7: F is a conjugate base of acid F. F is a weak acid. Weaker the acid, stronger the conjugate base. In hypophosphorus acid P is in +1 state (P) and in phosphoric acid(p) P is in +5 state but still P is stronger than P. Explain. A consideration of the structures of these acids explains the observed trend. P P The hydrogen atoms bonded directly to phosphorus are not acidic as the P bond is not polar enough due to equal electronegativity of phosphours and hydrogen. Acidity arises due to groups, one in P and three in P. The inductive effect of the single oxygen atom acts in the single bond in P but it is distributed over three bonds in P respectively. So bond in P much easily broken, explaining its higher acidity over P. Compare the acidity between Cl and As. Cl is much stronger than As, conjugate base of it more stabilised than conjugate base of As. pnitro phenol is stronger acid than phenol. Explain Conjugate base of pnitrophenol is more resonance stabilized than conjugate base of phenol (one more canonical from is possible for conjugate base of pnitro phenol). Compare the basic strengths of ortho, meta and para isomers of nitroaniline and predict the decreasing order of basicity. The N group which is a powerful electron withdrawing inductive effect when present at ortho and para positions for the interaction of the unshared pair of the amino nitrogen with the delocalised p-orbital system of the benzene nucleus is then enhanced. The neutral molecule is thus stabilized even further with respect to the cation, resulting in further weakening as a base. Thus the order of basicity of nitroanilines is as m-nc6n p-nc6n o-nc6+n. Which way would the p shift when AlCl is added to pure water? Write a net ionic equation to support your answer. AlCl + Al() Cl

6 Chemistry: Concepts of Acids and Bases-6 As it is clear from the above equation that aqueous solution of AlCl is acidic, so p will shift below 7. Problem 8: Write the formula for the conjugate acids of the following bases: (a) C (b) C (c) C55N (d) N 5. In each case the conjugate acid is formed from the base by the addition of a proton. a) C. This is a species which might form in liquid acetic acid upon addition of a strong acid. C. Note that C can serve as both an acid and a base. (c) b) d) CN 5 5. N. Note that bases, like acids, can be polyfunctional. The second 6 proton is accepted by N, however, only with great difficulty. Problem 9: a) Is a solution of AlCl in water acidic, basic, or neutral? b) Write a net ionic equation to support your answer. Problem 10: Problem 11: a) Acidic b) Al( ) [Al( ) ] or Al( ) [Al( ) ] When a strong acid dissolves in water, there are ions in the solution afterward. When a soluble metal hydroxide dissolves in water, there are ions in solution afterward. Besides the difference in the identity of the ions, what is the basic difference in these processes? The dissolving process causes the formation of the ions in the case of the strong acids; the ions are present from the beginning in the case of the metal hydroxides. The ionization constant of CN is given as The ionization constant of N + is Decide which is the stronger acid, CN or N +. N + is slightly stronger acid (Ka for N + = ). [Larger the value of ionization constant, stronger the acid will be.] Problem 1: Arrange o-nitro, p-nitro, m-nitrophenol in decreasing acid strength p-nitrophenol o-nitrophenol m-nitrophenol The N is electron withdrawing and acid strengthening. Its resonance effect, which occurs only from para and ortho positions, predominates over its inductive effect, which occurs also from the meta position between ortho and para derivative, para derivative is more acidic because increase of ortho the

7 Chemistry: Concepts of Acids and Bases-7 hydrogen of phenolic group is attached through hydrogen bonding with oxygen of N group and hence not possible to remove easily. Problem 1: Which is the stronger base towards a proton N or P and why? Problem 1: Problem 15: Problem 16: Problem 17: Bond energy (N P ) ionisation suggests that N will be stronger base. This is constituent with the relative strengths of the respective conjugate acids: N P. Why pyrole is less basic than pyridine? Pyrole uses lone pair of electron on nitrogen atom in delocalisation hence less electron are available for protonation, hence less basic than pyridine. Arrange according to increasing Lewis acid character, B(nBu), B(tBu) The highly branched tertiary butyl group involve appreciable back strain (Bstrain) when the boron atom changes to pyramidal environment on adduct formation. This destabilizes the adduct. ence the order is B(tBu) < B(nBu) Which of the following oxide is most acidic Ag, V5, C, N5 The oxide with the highest positive oxidation state on the element other than should be most acidic. xidation states of V in V5 and N in N5 are both +5. But the electronegativity of N is higher, making N5 the most acidic oxide. n the basis of -bonding explain that the second ionization constant K for fumaric acid is greater than for maleic acid. We know that -bonding involving acidic has an acid weakening effect and -bonding in conjugate base has an acid strengthening effect. Both dicarboxylic acids have two ionisable hydrogen atoms. Considering second ionization step. C C C C C C C C Fumarate monoanion (no -bonding) Maleate monoanion (-bonding) Since the second ionisable of the Maleate participates in -bonding more energy is needed to remove this because the -bond must be broken. The maleate mono anion is, therefore, the weaker acid.

8 Chemistry: Concepts of Acids and Bases-8 Assignments (New Pattern) SECTIN I Single Choice Questions 1. Consider the complete ionization of S (strong acid) and (C), oxalic acid (weak acid) in liquid N. S N N S (C) N N (C ) Liquid N is called : (a) proton-acceptor (b) leveling solvent (c) both (d) none of these.. ydrated proton cannot be (a) 5 (b) 9 (c) 5 (d) () n.. The strongest base that can exist in aqueous solution is : (a) N (b) Cl (c) (d) F.. Select correct statement: (a) NF is stronger base than N (b) N is stronger base than NF (c) N is always a base and NF an acid (d) N is always an acid and NF a base. 5. Among the following compounds, the strongest acid is (a) C C (b) C66 (d) C (c) C6 6. Amongst the following the most basic compound is (a) Benzyl amine (b) Aniline (c) Acetanilide (d) p nitro aniline 7. What is the decreasing order of strength of bases? (a) C C N > C C > (b) C C > C- C > N >

9 Chemistry: Concepts of Acids and Bases-9 (c) > N > - C C > CC (d) N > C C > > C -C 8. The following acids have been arranged in order of decreasing acid strength. Identify the correct order. Cl (I) Br (II) I (III) (a) I > II > III (b) II > I > III (c) III > II > I (d) I > III > II 9. f the following orders regarding basicity, which one is correct (a) CCN > PhCN > CCN (b) CCN > PhCN > CCN (c) CCN > PhCN < CCN (d) CCN < PhCN < CCN 10. Which among the following is the strongest base (a) aniline (b) N,N dimethyl amine (c) para nitro aniline (d) meta nitro aniline 11. Which of the following pairs represents the strongest acid and strongest base that can exist in water? (a) and (b) N and N (c) Cl and F (d) N and C C 1. Which of the following has been arranged correctly in order of increasing acidic strength? (a) CC NCC NCCC CC (b) CC CC NCCC NCC (c) CC NCCC CC NCC (d) NCC NCCC CC CC 1. Which of the following is arranged in order of increasing proton affinity? (a) S I N F (b) F I N S (c) I F S N (d) N S F I 1. Among the following, which is the strongest acid? (a) Cl () (b) Cl () (c) S() (d) S (). 15. Among the following, which is the most basic towards BMe? (a) MeN (b) EtN (c) (d) S. 16. NCC May behave

10 Chemistry: Concepts of Acids and Bases-10 (a) only as an acid (c) as an acid as well as a base 17. is capable to act as an acid with (a) N (c) C66 (b) only as a base (d) neither as an acid nor as a base (b) S (d) Cl 18. Which of the following species is an acid and also a conjugate base of another acid (a) S (b) S (c) (d) Which of the following has been arranged correctly in order of increasing basic strength? (a) C C N CC (b) C C CC N (c) N C C C C (d) N C C C C 0. Which of the carboxylic acid is the most acidic? (a) Acetic acid (b) Formic acid (c) Benzoic acid (d) Cyclopentane carboxylic acid. 1. The conjugate acid of S8 (a) S8 (b) S (c) S (d) S8. The following acids have been arranged in order of decreasing acid strength. Identify the correct order. Cl (I) Br (II) I (III) (a) I > II > III (b) II > I > III (c) III > II > I (d) I > III > II. Which of the following are amphiprotic in nature? (a) (b) P (c) S (d) F. Among the following compounds, the strongest acid is (a) C C (b) C66 (c) C6 (d) C 5. With reference to protonic acid which of the following statement is correct? (a) P is more basic than N (b) P is less basic than N (c)p is equally basic than N (d) P is amphoteric while N is basic SECTIN II May be more than one choice 1. Which of the following is a hard acid (a) C (b) Br (c) Fe + (d) Cd +. Which of the following statements is/are correct (a) I is a weaker base than F

11 Chemistry: Concepts of Acids and Bases-11 (b) is a stronger base N (c) N is a weaker base than N (d) FC: is a stronger base than ClC:. Which one of following is the strongest acid (a) Cl (b) Cl (c) Cl (d) Cl. The conjugate acid of S7 is (a) S7 (b) S (c)s6 + (d) S 5. Among the following weakest acid is (a) N (b) As (c) Sb (d) P 6. Increasing order of Lewis acid strength AlCl GaCl InCl I II III (a) I II III (c) II I III (b) III II I (d) III I II 7. Which one of following is the strongest acid (a) P (b) P (c) P (d) S 8. What is the decreasing order of strength of bases (a) C C N > C C > (b) C C > C- C > N > (c) > N > - C C > CC (d) N > C C > > C -C 9. Which of the following is a soft base? (a) RS (b) N (c) (d) Cu = 10. Amongst the following the most basic compound is N (a) (b) N N

12 Chemistry: Concepts of Acids and Bases-1 N C (c) (d) N N 11. Which of the following is strongest Lewis acid (a) C (b) F (c) N (d) 1. The conjugate base of + is (a) (b) (c) + (d) None of these 1. Acetic acid is a conjugate base of which acid. (a) CC (b) CCC (c) CC + (d) None 1. Conjugate base of N is (a) N (b) N + (c) N (d) N 15. Which of the following is the soft base? (a) C ion (b) C (c) Ce + (d) Pb Which among the following is the strongest base (a) Be() (b) Mg() (c) Ba() (d) Sr() 17. The conjugate acid of N is (a) N (c) N + (b) N (d) N 18. In the equilibrium CC + F C C + F (a) F is the conjugate acid of CC (b) F is the conjugate base of F (c) CC is the conjugate acid of C C (d) C C is the conjugate base of CC. 19. Which of the following statements is/are correct? (a) Maleic acid is a stronger acid than fumaric acid but maleate monoanion is a weaker acid than fumarate monoanion (b) Maleic acid is a stronger acid than fumaric acid and also maleate monoanion is a stronger acid than fumarate monoanion (c) Maleic acid is a weaker acid than fumaric acid but maleate monoanion is a stronger acid than fumarate monoanion

13 Chemistry: Concepts of Acids and Bases-1 (d) Maleic acid is a weaker acid than Fumaric acid and also maleate monoanion is a weaker acid than fumarate monoanion. 0. Which of the following is the strongest acid (a) N (c) N (b) S (d) All have same strength 1. Which of the following species is an acid and also a conjugate base of another acid (a) S (b) S (c) (d) +. Which of the following orders regarding acid strength is correct? (a) C < CC < PhC (b) C > PhC > CC (c) C > CC > PhC (d) CC > C > PhC. The following equilibrium is established when hydrogen chloride is dissolved in acetic acid. Cl + CC Cl + CC + The set that characteristics the conjugate acid-base pair is (a) (Cl, CC) and (CC + and Cl ) (b) (Cl, CC + ) and (CC, Cl ) (c) (CC +, Cl) and (Cl, CC) (d) (Cl, Cl ) and (CC +, CC). In the following compounds, the order of acidity is N C N (I) (II) (III) (IV) (a) III > IV > I > II (c) II > I > III > IV (b) I > IV > III > II (d) IV > III > I > II 5. f the following orders regarding basicity, which one is correct (a) CCN > PhCN > CCN (b) CCN > PhCN > CCN (c) CCN > PhCN < CCN (d) CCN < PhCN < CCN SECTIN III Comprehension Type Questions Write-up I Acids are the species capable of donating the proton in a reaction while bases are the species capable of accepting the proton in a reaction, i.e., acids are proton donors (protogenic) and bases are proton acceptors (protophilic). 1. The conjugate acid of S 8 is

14 Chemistry: Concepts of Acids and Bases-1 (a) S (b) S 8 (c) S (d) S. The conjugate base of P is (a) P (c) P. Proton donating species is called (a) acid (c) salt (b) (d) P P (b) base (d) none of these Write-up II A base is a substance which can furnish a pair of electrons to form a coordinate bond whereas an acid is a substance which can accept a pair of electrons. A Lewis acid is a substance that acts as an electron acceptor or electrophile while a Lewis base is a substance that acts as an electron donor or nucleophile.. Which of the following is a Lewis acid? (a) N (c) + (b) S (d) AlCl 5. BF is taken as an example of Lewis acid because it behaves (a) electrophile (b) nucleophile (c) neutral molecules (d) free radical 6. Which of the following is a Lewis base? (a) (c) N (b) Cl (d) C SECTIN IV Subjective Questions LEVEL I 1. Which of the following reagents are strong electrolytes? (a) N (b) NCl (c) C (d) NaC, (e) Cl (f) NaCl.. Arrange according to increasing Lewis acid character, SiF, SiCl, SiBr, Sil. Draw an electron dot diagram to illustrate that ammonium hydroxide could not exist as a weak base. Explain the weakly basic properties of a solution of ammonia in water.. The amino acid glycine exists predominantly in the form NCC. Write formulas for (a) the conjugate base and (b) the conjugate acid glycine. 5. Arrange according to increasing Lewis acid character, B(nBu), B(tBu)

15 Chemistry: Concepts of Acids and Bases Identify conjugate acid base pair in the following reactions C C65 Cl + + Cl 7. Write the equation representing self-ionisation of PCl and BrF as non-aqueous solvents. 8. Using the Lewis acid-base concept determine the trend in the acid strengths in the series: a) Cl, Cl, Cl b) P, P, P 9. Rationalize the relative Lewis basicities (Si) < (C); (b) (Si)N < (C)N. 10. Be() exhibits amphoterism. Explain by reactions. LEVEL II 1. Identify the Lewis acid and base in the reaction BrF + F [BrF].. If you mix equal concentration of reactants and products which of the following reactions proceed to the right and which proceed to the left? a) S (aq) N (aq) N (aq) S (aq) b) C (aq) S (aq) S (aq) C (aq). In the acid of the type A, at 5 C [ + ] = 1 10 M. What is [ ]?. ydration of CuS is a Lewis acid-base reaction. Explain. 5. Boric acid B is dissolved in water. ow does it behave? 6. Arrange the following in the order of their basic strength. Justify your answer NN,N,N 7. Account for the trend in acidity [Fe()] [Fe()] [Al()] [g()] n 8. Silver perchlorate, AgCl, is significantly more soluble in benzene than in alkane solvents. Account for this observation in terms of Lews acid-base properties. 9. The common ores of nickel and copper are sulphides. In contrast, aluminium is obtained from the oxide and calcium from the carbonate. Can these observations be explained in terms of hardness? 10. In the traditional scheme of qualitative analysis, a solution of metal ions are oxidized and then aqueous ammonia is added to raise the p. The ions Fe +, Ce +, Al +, Cr +, and V + precipitate as hydroxides. The addition of and Na re-dissolves the aluminum, chromium, and vanadium. Discuss these steps in terms of the acidities of oxides. SECTIN V Miscellaneous Questions

16 Chemistry: Concepts of Acids and Bases Match the following a) BF i) Cationic Bronsted base b) N ii) Cl c) iii) P d) [Al()5] + iv) Ag + e) Monobasic acid v) Bronsted acid f) Soft acid vi) g) ard base vii) Lewis acid h) Neutralisation viii) Amphiprotic. Fill in the blanks a) According to Arrhenius acid-base theory, in neutralization reaction. molecule is formed. b). acid-base theory cannot define that N is a base c) In the reaction, BCl + P ClB:P, the Lewis base is. d) In the reaction, SnCl + Cl SnCl + e, the Lewis acid is. e) The conjugate acid of P is. f) The basicity of phosphorous acid (P) is. Answers to Assignments SECTIN - I 1. (c). (c). (b). (b) 5. (a) 6. (a) 7. (a) 8. (a) 9. (a) 10. (b) 11. (a) 1. (b) 1. (c) 1. (a) 15. (a) 16. (c) 17. (a) 18. (a) 19. (a) 0. (b) 1. (d). (a). (a). (a) 5. (b) SECTIN - II 1. (a), (c). (a), (c), (d). (d). (a) 5. (c) 6. (b) 7. (c) 8. (a) 9. (a) 10. (a) 11. (a) 1. (a) 1. (c) 1. (a) 15. (b) 16. (c) 17. (c) 18. (b) 19. (a) 0. (b) 1. (a). (b). (a). (d) 5. (a) SECTIN - III 1. (a). (b). (a). (d) 5. (a) 6. (a) SECTIN - IV

17 Chemistry: Concepts of Acids and Bases-7 1. (b), (d), (e) and (f). LEVEL I. The order in this case is the reverse of that for BX. -conjugation from the halogen p-orbital to the Si-d orbital is not as intense as in the case of BX and the order of acidity follows the increase in electron withdrawing power of the halogen from I to F. ence the order is SiI < SiBr < SiCl < SiF. N The diagram shows that there is no covalent bonding of the ion to the N ion. Since solutions of ammonia in water do not act as strong bases, this representation must be incorrect. The fact that ammonia acts as a weak base is explained by the equilibrium. N N. (a) NCC (b) N C C 5. The highly branched tertiary butyl group involve appreciable back strain (B-strain) when the boron atom changes to pyramidal environment on adduct formation. This destabilizes the adduct. ence the order is B(tBu) < B(nBu) 6. (Base) (conjugate acid) C(Acid) 6 5 C 6 5 (conjugate base) Cl (acid Cl (conjugate base) (Base) (conjugate acid) 7. PCl PCl PCl, BrF BrF BrF 8. As a general rule, the greater the number of terminal oxygens in the Lewis structure of oxy acid, the greater is its acidity. Thus, in a) Cl Cl Cl three terminal oxygen two terminal oxygen one terminal oxygen b) P P P one bonded to, two bonded to three bonded to All have only one terminal oxygen. Also electronegativity of and P are also approximately same. ence, there is not large difference in the strengths of the acids.

18 Chemistry: Concepts of Acids and Bases-8 9. Nonmetallic elements in period and below can expand their valence shells by delocalization of the or N lone paris (7), so the silyl ether and silyl amine are the weaker Lewis bases in each pair. 10. Be() is an amphoteric hydroxide since it reacts with both acids and bases. Be() (s) Be (aq) ( ) Be() (s) (aq) Be() (aq) 1. The acid BrF adds the base : F. LEVEL II. a) From S is stronger acid than N and N is stronger base than b) S (aq) N (aq) N (aq) S (aq) stronger acid stronger base wea ker acid wea ker base S. Thus, Since proton transfer takes place from stronger acid to stronger base, the reaction proceeds from left to right. C (aq) S (aq) S (aq) C (aq) stronger acid stronger base wea ker acid wea ker base This is reverse of (a), hence, proceeds right to left.. A(aq) ( ) (aq) A (aq) Since, and [ ][ ] K 1 10 at 5 C 1 w [ ] 1 10 M, hence, K 110 [ ] 1 10 M 1 w 1 [ ] 110. ydration of metal ions in solution is in itself a Lewis acid-base reaction. Thus, when CuS dissolves in water, each Cu ion is associated with six water molecules as Cu() 6. In this case, the Cu ion acts as the acid and the molecules as the base. CuS 6 [Cu( ) ]S (aq) acid 6 base 5. Boric acid is an oxoacid weak acid with the following structure? C B It does not ionize in water to produce ion. Its reaction with water is: B() (aq) ( ) B() (aq) (aq) In this Lewis acid-base reaction, boric acid accepts a pair of electrons from the hydroxide ion that is derived from the molecule. 6. N N N N

19 Chemistry: Concepts of Acids and Bases-9 7. The weakest acid is the Fe complex on account of its relatively large radius and low charge. The increase of charge to + increases the acid strength. the greater acidity of Al can be explained by its smaller radius. the anomalous ion in the series is the g complex. This complex reflects the failure of an ionic model, for in this complex there is a large transfer of positive charge to oxygen as a result of covalent bonding. 8. The electrons of benzene, a soft base, are available for complex formation with the empty orbitals of the cation Ag, a soft acid (recall 19). The species [Ag C6 6] is the complex of the acid Ag with electrons of the weak base benzene. 9. We know that and Cu are considerably softer acids than rule accounts for the sorting observed. C are hard bases; S is a soft base. The cations Al or Ni and Ca. ence the hard=hard and soft-soft 10. When the oxidation number is +, all the metal oxides are sufficiently basic to be insoluble in a p 10 solution. Aluminum (III) is amphoteric and redissolves in strong base to give aluminate ions, [Al() ]. Vanadium (III) and chromium (III) are oxidized by to give vanadate ions, [V ], and chromate ions, [Cr ], which are the anions derived from the acidic oxides V 5 and Cr, respectively. SECTIN - V 1. (a vii)l (b v); (c viii); (d i); (e iii); (f iv); (g ii); (h vi). a) Water b) Arrhenius c) P d) SnCl e) P f)