Question

CH3NH2 4.2x0 CH3NH3 CHisON 5.9x10 CHsO, 08 7.77 CSHsN 1.5x10 CHNH 6.7x106 5.17 2.4x10 10.62 NH 1.7x1 How many grams of the bromide salt of the conjugate acid must be combined with how many grams of the weak base, to produce 1.00 L of a buffer that is 1.00 M in the weak base? grams bromide salt of conjugate acid grams weak base-

Answer 1

Ans. #1. Choice of weak base: Choose the weak base that of its pKa closest to the pH of the buffer because the buffer capacity is maximum when pKa is closest to pH.

So, chose of weak base = C₆H₁₅O₃N

Henderson- Hasselbalch equation Where B weak base BH Conjugate acid Given, pH7.130 Kb5.90E-07 Total volume of buffer 1000.0 mL pOH 6.87 pKb6.23 Step 1: [BH ] antilog (pOH -pkb)10 064 4374 Or, BH]- 4.374 [B] - Equation 1 Step 2: Given, [B] 1.00 M So, using equation 1 - [BH4.374 x 1.00 M4.374 M Now, Required mass of B (Molarity x Vol. in liters) x MW M 1.00 x 1.00 LX 149.19004 g m149.190g Required mass Br-salt of BH (Molarity x Vol. in liters) x MW 37 M x 1.00 360.12624 g mo1575.095 g

#2. Choice of weak acid: Choose the weak acid that of its pKa closest to the pH of the buffer because the buffer capacity is maximum when pKa is closest to pH.

So, chose of weak acid = HC₂O₄^-

#3. Choice of weak acid: H₂PO₄^-