Calculate the pH of a 0.500 L of a 0.200 M NH_4^+ - 0.200 M NH_3 buffer before a

Question

Calculate the pH of a 0.500 L of a 0.200 M NH_4^+ - 0.200 M NH_3 buffer before and after the addition of 0.0050 mol NaOH. Assume the volume remains constant. Consider the titration of 100.0 ml of 0.016M HOCl (k_1 = 3.5 times 10^-6) with 0.040 M NaOH. Calculate the pH: a) After addition of 10.0 ml of 0.0400 M NaOH b) Halfway to the equivalence point c) At the equivalence point In a 0.15 M NH_3, the pH is 11.21 and the percent dissociation is 1.1%. Calculate the concentrations of all species present, the pH, and percent dissociation of ammonia in a solution that is 0.15 M in NH_3, and 0.45 M in NH_4Cl. Calculate the pH of 5.0 times 10^-5 M Ba(OH_2) Calculate the pH of 0.010 M Benzoic Acid at 25 degree C where K_a = 6.3 times 10^-5 at degree C. Calculate the pH of a 0.050 M solution of CH_3CO_2 Na where K_a = 1.8 times 10^-5 at 25 degree C.

Explanation / Answer

Question 3.

pH for NH4+ = 0.2 Mand NH3 = 0.2 M

before additino of 0.005 mol of OH-

first, apply buffer equation

pOH= pKb + log(NH4+/NH3)

pOH = 4.75 + log(0.2/0.2)

pOH = 4.75

pH = 14-pOH = 14-4.75 = 9.25

after addition:

mol of NH4+ = MV = 0.5*0.2 = 0.1 mol

mol of NH3 = MV = 0.5*0.2 = 0.1 mol

after ading:

mol of OH- = 0.005

mol of NH3 = 0.1+0.005 = 0.105

mol of NH4+ = 0.1-0.005 = 0.095

pOH = 4.75 + log(0.095/0.105)

pOH = 4.70653

pH = 14-pOH = 14-4.70653 = 9.29347

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