Deduce Alkaline Buffer on Mixing 2 Solutions

A buffer is a solution that maintains pH when small amounts of H+ or OH- is added to it. It is essentially a mixture of conjugate acid-base pair: a. acidic buffer = weak acid + conjugate base b. alkaline buffer = weak base + conjugate acid The acid will remove OH- added while the base partner will remove H+ added, thereby maintaining pH. For this question we need to determine the resultant solution when 2 solutions are mixed. A useful way to determine resultant solution is using the ICE table when there is an acid-base reaction. A. 10 cm3 of 0.1 mol dm-3 NaOH and 20 cm3 of 0.2 mol dm-3 NH4+Cl- NaOH is a strong base while NH4+ is conjugate acid of weak base NH3. Resultant solution is 0.001 mol of weak base NH3 + 0.003 mol conjugate acid NH4+. This is an alkaline buffer and can be our answer but let's go through the other options first. B. 25 cm3 of 0.1 mol dm-3 NaOH and 50 cm3 of 0.1 mol dm-3 CH3CO2-Na+ NaOH is a strong base while CH3CO2- is conjugate base of weak acid CH3COOH. Resultant solution is a mixture of 2 bases which cannot function as a buffer. C. 10 cm3 of 1 mol dm-3 H2SO4 and 20 cm3 of 1 mol dm-3 CH3CH2NH2 H2SO4 is a strong acid while CH3CH2NH2 is a weak base. Resultant solution is 0.02 mol of conjugate acid CH3CH2NH3+ which is not a buffer. D. 50 cm3 of 0.05 mol dm-3 NaOH to 50 cm3 of 0.10 mol dm-3 CH3NH3+Cl- NaOH is a strong base while CH3NH3+ is conjugate acid of weak base CH3NH2. Resultant solution is 0.0025 mol of weak base CH3NH2 + 0.0025 mol of conjugate acid CH3NH3+. We have another alkaline buffer and the moles of weak base and conjugate acid are exactly the same. This buffer is at its maximum buffering capacity so pH will be a constant and can best resist changes to pH. Therefore answer to this question is option D. Topic: Buffer Solution, Physical Chemistry, A Level Chemistry, Singapore Please SUBSCRIBE to my channel and SHARE this video with your friends if you find it helpful! View the full video with description at my website https://chemistryguru.com.sg/det-alkaline-buffer-on-mixing-2-solution Looking for more FREE A Level Chemistry videos? Check out our huge collection of video lessons at https://chemistryguru.com.sg/a-level-chemistry-video-lessons