In: Chemistry
for the titration of 10.0 ml of .15 M HNO2 aqueous solution (Ka=7.2x10^-4) using 2.5 M NaOH aqueous solution, consider the following points of the titration: A: Initial pH of .15 M HNO2 aqueous solution B: .1 mL added base C: 1/2 equivalence point D: Equivalence point E Excess base (assume added 100.0 mL of base)
Set up the init mol, final mol, total volume, and ICE table for points B and D only:
Point B:
Titration equation:
init mol:
(assume reaction goes to completion)
final mol:
total volume:
flip reaction equation:
I:
C:
E:
Point D:
Titration equation:
init mol:
(assume reaction goes to completion)
final mol:
total volume:
flip reaction equation:
I:
C:
E:
Point-B:
Titration equation: HNO2 + NaOH(aq) ----- > NaNO2(aq) + H2O
Initial moles of HNO2 = MxV(L) = 0.15 mol/L x 0.010 L = 0.0015 mol
Initial moles of NaOH during mixing = MxV(L) = 2.5 mol/L x 0.00010 L = 0.00025 mol
0.00025 mol of NaOH will react with 0.00025 mol of HNO2 to form 0.00025 mol of NaNO2(aq)
Hence
Final mol of HNO2 = 0.0015 mol - 0.00025 mol = 0.00125 mol
Final mol of NaOH = 0.00025 - 0.00025 = 0 mol
Total volume of solution = 10.0 mL+ 0.1 mL = 10.1 mL = 0.0101 L
--- HNO2 + NaOH(aq) ----- > NaNO2(aq) + H2O
I: 0.0015, 0.00025 mol, ----- 0 ------------ N.A
C: - 0.00025, - 0.00025 mol, + 0.00025, + 0.00025 mol
E: 0.00125 mol, 0 mol, ---------- +0.00025 mol, N.A
At equilibrium, [HNO2] = 0.00125 mol / 0.0101 L = 0.124 M
Point-D:
Titration equation: HNO2 + NaOH(aq) ----- > NaNO2(aq) + H2O
Initial moles of HNO2 = MxV(L) = 0.15 mol/L x 0.010 L = 0.0015 mol
Hence moles of NaOH required to reach the equivalence point = 0.0015 mol
=> MxV = 2.5 mol/L xV = 0.0015 mol
=> V = 0.0015 / 2.5 = 0.6 mL NaOH
Initial moles of NaOH during mixing = MxV(L) = 2.5 mol/L x 0.00060 L = 0.0015 mol
0.0015 mol of NaOH will react with 0.0015 mol of HNO2 to form 0.0015 mol of NaNO2(aq)
Hence
Final mol of HNO2 = 0.0015 mol - 0.0015 mol = 0.00 mol
Final mol of NaOH =0.0015 mol - 0.0015 mol = 0.00 mol
Total volume of solution = 10.0 mL+ 0.6 mL = 10.6 mL = 0.0106 L
--- HNO2 + NaOH(aq) ----- > NaNO2(aq) + H2O
I: 0.0015, 0.0015 mol, ----- 0 ------------ N.A
C: - 0.0015, - 0.0015 mol, + 0.0015, + 0.0015 mol
E: 0.00 , 0.00 mol, ---------- +0.0015 mol, N.A