In: Chemistry
1.How many mL of 0.500 M HCl should be added to 155 mL of 0.0500 M benzylamine to form a buffer with pH = 8.52? C7H7NH2 pKb = 4.35 C7H7NH2 (aq) + H+ (aq) C7H7NH3 + (aq) This structure of benzylamine has a carbon at the junction of each line with 1 hydrogen on each 3-bonded ring C and 2 hydrogens on the C in the side chain attached to the ring carbon. Note that the N atom has 3 bonds and a lone pair.
2.Write the formula for the conjugate acid of benzylamine.
benzylamine millimoles = 155 x 0.05 = 7.75
millimoles of HCl = 0.5 x V = 0.5 V
C7H7NH2 (aq) + H+ (aq) -----------------> C7H7NH3 + (aq)
7.75 0.5 V 0
7.75 - 0.5V 0 0.5V
pH = 14 – { pKb + log[salt/ base ]}
8.52 = 14 - {4.35 + log [0.5V / 7.75 - 0.5V]
[0.5V / 7.75 - 0.5V] = 13.49
V = 14.43 mL
volume of HCl added = 14.43 mL