Explanation Here, according to the given question Caffeine is a weak base. We can say that Caffeine dissociates in water according to the reaction C 8 H 10 N 4 O 2 ( a q ) + H 2 O ( l ) ↔ C 8 H 11 N 4 O 2 + ( a q ) + O H − ( a q ) Since, pK b for the reaction is given we can calculate the K b (dissociation constant) for the reaction. Now using the concentration of Caffeine and molar mass of Caffeine, we can calculate the molarity of Caffeine. Now, calculate the [ OH − ] by constructing the ICE table. After calculating [ OH − ] we can calculate the pOH using the logarithmic table. Finally we can calculate the pH using the pOH value. Given: pK b for Caffeine is 10.4 Concentration of Caffeine is 455 mg/L Formula used: Molar mass can be calculated by adding the atomic mass of all the elements The dissociation constant K b can be calculated by pK b = -log K b K b = 10 −pKb Molarity can be calculated using the formula M o l a r i t y = C o n c e n t r a t i o n ( m g L ) M o l a r m a s s × 1000 xs The relation between dissociation constant K b and equilibrium concentration is K b = [ P r o d u c t ] [ R e a c t a n t ] The pOH can be calculated as pOH = - log[ OH − ] The pH can be calculated as pH + pOH = 14 Calculation: Here, pK b = 10.4 pK b =- log K b K b = 10 −pK b K b = 10 −10.4 K b = 3.981 × 10 −11 For Caffeine ( C 8 H 10 N 4 O 2 ) Atomic mass of C = 12 g/mol Atomic mass of H = 1 g/mol Atomic mass of N = 14 g/mol Atomic mass of O = 16 g/mol Molar mass of C 8 H 10 N 4 O 2 ) = (12×8)+(1×10)+(14×4)+(16×2) = 194 g/mol M o l a r i t y = C o n c e n t r a t i o n ( m g L ) M o l a r m a s s × 1000 M o l a r i t y = 455 m g L 194 g / m o l × 1000 Molarity = 0...

Chemistry: Structure and Properties Custom Edition for Rutgers University General Chemistry

15th Edition

ISBN: 9781269935678

Author: Nivaldo J. Tro

Publisher: Pearson Education

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Chapter 17, Problem 93E

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The pH of a solution containing a caffeine concentration of 455 mg/L

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Chapter 17, Problem 92E

Chapter 17, Problem 94E

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Chemistry: Structure and Properties Custom Edition for Rutgers University General Chemistry

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The pH of a solution containing a caffeine concentration of 455 mg/L

Solution Summary: The author explains that Caffeine is a weak base and can be dissociated in water according to the reaction C 8 H 10 N 4 O 2 + H 2 O

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To determine: The pH of a solution containing a caffeine concentration of 455 mg/L

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Chapter 17 Solutions

To determine:

The pH of a solution containing a caffeine concentration of 455 mg/L