Question

Problems Three & Four

Problem Three: Calculate the expected pH of a 0.100 M solution of ammonium chloride given that Kb for ammonia is 1.76 x 105. pH = Problem Four: 0.100 moles of NaOH are combined with 0.125 moles acetic acid. The mixture is tal mixture is taken to a final volume of 100.0 ml. What is the expected pH of the solution? Use K, for acetic acid of 1.76 x 10-5 pH-

Answer 1

---K21.76X10-5 We want to find ka of NH gi. We know, kayko 216-14 on kos 10-14 z 10-" E 50168 x 10** K 176x10-5 Now, which will disscriate into what and u- - NHAU NH₃ + tu- NH4t will hydrolyse water - NHAT + H₂o NH3 + H₂ _ _ = [NM ][ M304] - [NH 4 + Assuming, I wHs] = [Hs o*] kaz Chaot] ² [NH₂+] an [ H, 6*] =Kax En xt] - 5.68x10-x 0.1 - 7.53 x 10-6 M Now,PH = -log[1, 0) = -log (7.53 x10069 _ PH = 512 2 5112

NaOH + + H₂O CH₂ CEDH 0.125 CH₂ Loona O Moles at t-D 0-100 HE UDH At, tot' : 0.025 Thus, system will contain 0,100 moles of the Loo Na and 0.625 moles of Thus, they will form af buffer pH of buffer solution can be found from Henderson - Hasselbalch equation - pH = pka + log [ 4, Loo Na] - [ CHE LODH] on pH = pka + log 0.100 0.025 New, for Autic and, ka= 1176x10 s I an pka = -log ka = -log (1.76 x 16-5) = 4.75 .: pH = 4.75 + log 0.100 0.025 on pH = 5.35

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