Question

Determine the pH change when 0.049 mol HCl is added to 1.00 L of a buffer solution that is 0.332 M in HF and 0.231 M in F". pH after addition - pH before addition = pH change = Submit Answer Retry Entire Group 9 more group attempts remaining

Answer 1

a) Concentration of HF ,[HF ] = 0.332M Concentration of F, [F]=0.231 M PK, of HF = -log K = -log(7.20x10+) =3.14 According to Henderson equation F- pH = pK, + log = 3.14+ log 0.231 = 2.98 -- -------- ------------ ----- Concentration of Hadded = 4.172 mol = 0.049 M 1.00 L + —— + H2O ICE table: F I(M): 0.231 C(M) -0.049 E(M): 0.182 H+ 0.049 -0.049 0 HF 0.332 +0.049 0.381 [F] According to Henderson equation, pH = pK, + log (HF] = 3.14+1 = 3.14+ log 0.182 381 = 2.82 Change in pH = 2.82 -2.98 = -0.16 Thus, pH is decreased by 0.16 units

===========================================================

b) Inital pH Concentration of CH NH,, (CHNH2) = 0.362 M Concentration of CH NH;, [CH NH} ] = 0.433 M PK, of CH NH, = 14.00-pK = 14.00-9.36 =4.64 According to Henderson equation, pH = PK, + log [CH NH] [C,H,NH] 0.362 = 4.64+108 0433 = 4.56 --- -- ------ -------- ---------- ------- 0.096 mol = 0.096M Concentrati on of OH- added= 1.00 L ICE table: CHÚNH + OH- Initilal (M) 0.433 0.096 Change (M) -0.096 -0.096 Equil(M): 0.337 → C.H.NH, + 4,0 0.363 +0.096 0.459 [CH,NH, According to Henderson equation, pH = pK+log [C,H,NH] 0.459 = 4.64+108 0337 = 4.77 Change in pH, ApH = 4.77-4.56 = 0.21 Thus, the pH is rised by 0.21 units after the addition of base