Question

Given that at 25.0 ∘C

• Ka for HCN is 4.9×10^-10
• Kb for NH3 is 1.8×10^−5
  - Part C Calculate the pH of a 0.20 M solution of KCN at 25.0 °C. Express the pH numerically using two decimal places. View Available Hint(s) Templates Symbols uido redo reset keyboard shortcuts help pH = Submit Request Answer - Part D Calculate the pH of a 0.20 M solution of NH Brat 25.0°C. Express the pH numerically using two decimal places. View Available Hint(s) Templates Symbols uido redo reset keyboard shortcuts help pH = Submit
  

Answer 1

[Part-c) first, we know that, KCN tten Now, Kenie, kt+ en H HCN (will be formed) so, Now we have to draw the ICE chart. CNO + H₂O = HCN (aq) + oH I 0.20 Water given, isa ka= 4.9x100 x x for HEN E 020-2 ignore H2O and we know that I ka.kb= kw through this chart the equation will be Kb= [HEN] [OH-] (410x10 10 Jakb= loxio [ CN- . Ky=2.04810 Now, we have to put the Ky value and concentration values. 2 كيا والا - so we will

ch O'20-2 [HCN] [oho We can eliminate the x [NO ] term by wring 5 to approximation = 2044105 = x² process. so, the equation will become » 2'DAxios = x 20 => x= 4:00x100 x = 2'02x10 3M OKO We know that pot = -log[ore ] = -log [2.02x10 3 poh - 2.69 or we can calculate the value of througth the value of . the pH, We know that, pH + por = 14. pH =(19-269) = 11:31 Hence, the pH of a 0.20M solation of KCN will be 11 31 (Annier Part-D To calculate the pH of a 0:20M solection of NH 4 R first we know that, NHA BY WHAT + BO - Acidic) Now, Like previous problem we have to draw the ILE chart NH & caq) + H₂O + NH3 + H30+ 1 0.20 similianly l o o we will not (0:20-x) as it is a liquid I No, ka= [NH 3] [H3O+] given, Kb= 1.8x10-5 Kakb= kw Kax(18810-5)= 10x100 so, ka= 5.55810-10 consider this [NHAT

I hope these two answers are helpful to you... Thanks... :)

Now, we can put the ka value to the equation, => ka=[NH 3] [H3O+] - [NHAT 5'56*10-10 = x² 0. 20-2 5.56810-10 = x² I using 5% approximation We can eliminate the x term] 020 x= 105x105 = [H3O+] Now, we know that, pre = - Loq [H3O+] pH = -log[rostios pH = 4107 Hence, pH of the 0.20M NHA Br solution will be 4'97) [Answer