Ans_Ex8 - Nielsen CHM1041 Answer to Exercise Set # 8 Ionic...

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Nielsen Bhaskar/PC/1713J/A 2/05 1 CHM1041 Answer to Exercise Set # 8 Ionic Equilibria II 1. Explain why water solutions of HCl and HClO 4 are practically equal in acid strength, even though HClO 4 is known to be a much stronger acid in certain other solvents. () ( ) 2 HO +1 -1 23 ga q a q HCl + H O H O + Cl 100% ionization ⎯⎯⎯→ 2 +1 -1 4 4g aq HClO + H O H O + ClO 100% ionization Both HCl and HClO 4 are much stronger acids than H 3 O +1 , and both essentially ionize completely in water solution to form this weaker acid. H 3 O +1 is the only acid present in significant concentrations and consequently it may be said that HCl and HClO 4 have been “leveled” to the same strength. 2. Write the equations illustrating the dissolution of the following salts in water. Indicate which ions undergo hydrolysis, which do not, and write an equation describing each hydrolysis. State if the resulting solution is acidic, basic, or neutral. (a) Na 2 S 2 +1 2 sa Na S 2 Na q N a + is a Group IA ion, low charge density, and does not undergo appreciable hydrolysis. S –2 , the conjugate base of the weak acid HS –1 , undergoes extensive hydrolysis: -2 -1 -1 2 S+HO H S+O H B a s i c U (b) 3 2 Cu NO 2 4aq +2 -1 32 2 3aq 2g Cu NO + 4 H O Cu H O + 2 NO N O 3 –1 is the conjugate base of the strong acid HNO 3 and is therefore a very weak base. Consequently, NO 3 –1 suffers little hydrolysis. Cu +2 ion is small and highly charged, coordinates with a specific number of water molecules, and polarizes the O-H bonds of water to the enhancement of acidity: () () +2 +1 +1 22 2 3 43 Cu H O + H O Cu H O OH + H O Acidic U
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Nielsen B h a s k a r / P C / 1 7 1 3 J / A 2 / 0 5 2 a q i c 2 (c) CsBr ( ) () 2 HO +1 -1 sa q a q CsBr Cs + Br neutral ⎯⎯⎯→ C s +1 is a large, diffuse Group IA cation and Br –1 is the conjugate base of the strong acid HBr. Neither ion undergoes significant hydrolysis. (d) KF ( ) 2 +1 -1 q KF K + F K +1 is a Group IA ion and undergoes little hydrolysis as a result of its low charge density. F –1 is the conjugate base of the weak acid HF, and hydrolyzes as follows: -1 -1 2 aq F+ H O H F + O H B a s U (e) NH 4 NO 3 ( ) 2 +1 -1 4 3s 4aq 3aq NH NO NH + NO N O 3 –1 is the conjugate base of the strong acid HNO 3 and does not experience significant hydrolysis. NH 4 +1 is a cation with removable hydrogens. It is also the conjugate acid of a moderate-strength base, NH 3 : +1 +1 42 3 3 aq NH + H O NH + H O Acidic U (f) 33 CH NH Cl ( ) +1 -1 3 s 3 aq aq CH NH Cl CH NH + Cl C l - conjugate base of strong acid HCl, no hydrolysis; - conjugate acid of moderate base, , that undergoes the following hydrolysis: +1 CH NH 3 CH NH +1 +1 2 3 32 CH NH + H O H O + CH NH Acidic U (g) 4 2 NH S ( ) 2 +1 -2 4 s 4 aq aq 2 NH S 2 NH + S B o t h N H 4 +1 and S -2 Undergo hydrolysis, but S -2 is a stronger base (K b = 1) than NH 4 + is an acid (K a = 5.6 x 10 -10 ); therefore, S -2 should hydrolyze to a greater extent than NH 4 +1 .
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This note was uploaded on 12/12/2011 for the course CHM 2041 taught by Professor Staff during the Fall '09 term at Santa Fe College.

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Ans_Ex8 - Nielsen CHM1041 Answer to Exercise Set # 8 Ionic...

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