strong base is dissolved in 775 mL of .200 M Ka= 4.97 Strong base dissolved in 7
ID: 969022 • Letter: S
Question
strong base is dissolved in 775 mL of .200 M Ka= 4.97 Strong base dissolved in 775 mL of 0.200 M weak acid (K_a = 4.97 x 10^-6) to make a buffer with a pH of 4.08. Assume that the volume remains constant when the base is added HA(aq)+OH^-(aq) Rightarrow H_2O(l)+ A^-(aq) Calculate the pK_a value of the acid and determine the number of moles of acid intially present pKa = mol HA When the reaction is complete. what the the concentration ratio of conjugate base to acid? [A^-]/[HA] = How many moles of strong base were initially added? mol OH^-Explanation / Answer
no of mol of weakacid (HA) initially = 775/1000*0.2 = 0.155 mol
pka = -log(4.97*10^-5) = 4.304
pH = pka + log(salt/acid)
4.08 = 4.304 + logx
x = 0.597 = salt/acid
No of mol of base added = x mol
0.597 = x/(0.155-x)
x = 0.058 mol
No of mol of base added = 0.058 mol
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