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105b_1999_e3_blank reisler

105b_1999_e3_blank reisler - 1 1 16 points(a How many moles...

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1 1. 16 points (a) How many moles of NaCN must be added to 1.00 L of 0.50 M HCN solution to give a buffer of pH = 9.00? K a (HCN) = 7.20x10 -10 (b) Write reactions that show how a buffer made of HCN and NaCN reacts when: (i) a strong acid is added (ii) a strong base is added
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2 (2) (14 points) A 1.00 L buffer solution was prepared from 0.31 M NH 3 and 0.26 M NH 4 F. 0.10 mol of H + ions were added to the solution (without changing the volume). Calculate the pH of the final solution. K b (NH 3 )= 1.8x10 -5
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3 3. (14 points) Ag 2 SO 4 dissolves in water to the extent of 8.7x10 -5 mol/L. a). Calculate K sp for this salt. b). What is the molar solubility of this salt in a 0.1 M solution of AgNO 3 ?
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4 4. (10 points) When ignited, solid ammonium dichromate decomposes in a fiery display (the "volcano reaction"), according to the reaction: (NH 4 ) 2 Cr 2 O 7 ( s ) Cr 2 O 3 ( s ) + 4H 2 O( l ) + N 2 ( g ) The thermodynamic values for this reaction are: Substance D H f 0 (kJ/mol) S 0 (J/mol.K) Cr 2 O 3 ( s ) –1140 81.2 H 2 O( l ) –242 118.7 N 2 ( g ) 0 191.5 (NH 4 ) 2 Cr 2 O 7 ( s ) –22.5 113.7 Calculate D G 0 for this reaction
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5 (5) (18 points) (a)
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