Question

A buffer solution contains NH3 0.20 M and NH4 + 0.30 M. Calculate the pH after 2.0 mmol of HCl is added to that solution. The volume of the solution is 50.0 mL and pKa (NH4 +) = 9.25


A
4.89

B.
8.92

C.
9.02

D.
9.07

E
9.58

Answer 1

Here Nhat is a weak acid and NH3 is it's Conjugate base This Wear acid and its conjugate base Forms a buffer solution. NH4+ + oH NH3 + H2O Base conjugate Conjugate Acid acid base According to Henderson- Hassel batch eanation, pH of the buffer solution. PH I conjugate base] pk at log [Weak acid] Here, pH = -10g (ka) + log (Initat] [NH₂ Here, pka of what 9.25 op-100 (wa) [NH₂] = 0.20 M, In tut] = 0.30m ph 9.25 + log 0.20N 0.30h = 9.25 +0.176) ( 9.074 Now in the solution 2 m mol of Hel 1 m mol = 10-3 moi 2 mmola 2x 10-3 mol NOW 'Hera, added Hu will react with NH 3 and it will form what

So concentration of NH3 will decrease and it concentration of what will increase. to. NH3 (aq) + HCl Nhut (41) + ci-(as) No or mores of NH₃ in the buffer solurion volume of solution 50.0 morni 0.05 L Molar Concentration of NH3 = mores of NH3 in 0.05L o 0:20 M 10.00 0.20 mols NH3 0.05% Solution Х 1 \ Soyution 0. ol moles NH3 mous of Nhat in the buffer solution volume of solution = 0.05L;1440 molar concentration of what=0.30M mous of Nhut in 0.05LO 0.30 mures what oosy solutish 1 x solytion 0.015 mokes NH47 - We add 0.002 mol In the buffer solution HCl which react with 0.01 mole NH3 NH3t HU Nhut tur CSwitce

No افر Now decrease in moes of NH3 murart mary of moles of NH3 to orlad roro (0:0) moles 0.002 moies Printed in 0.008 0.008 mae's maréis Of AH2 5) in crease in moes of mores of what ot mous of what mpino) (0.015 + 0.002) maisto more 2 = 0.017 moves of NHUT Volume or solution is a 0.05 L NOW molar concentration of NHST 0.017 moves of what [NHut] = 0.05L solution 2 0:34 (M) what NOW molar concentration of NH3 0.008 moles of NH3 [WH3] Oius L Soluhim 0.16 (M) AH3 CS Scanned with CamScanner

According to Henderson - Hasselbalch eanation, pH of the butter solution. pH 2 P Kat log [NH₃ ] [What Init3] • Inhat ja osum 0.16M Pka of NHLt = g. 25 PH 6.36M D 9.25+ log = 9.25+ (-0.33) 0.34 M 8.92 the pH of the solution after added Hq B 8.92 . CS Scanned with CamScanner