Question

Question 13 (2 points) A basic buffer is prepared by adding 0.7185 g of NH4Cl to 1.00 L of 0.4490 M NH3. Kb (NH3) = 1.8 x 10-5. Calculate the pH of the buffer. Provide your answer to two places after the decimal. Your Answer: Answer Hide hint for Qugstion 13 You must convert the mass of ammonium chloride into molarity. Also, you need to calculate the K, of ammonium ion from the Kb value of ammonia.

Answer 1

0 The question is solved by using Henderson- Hazelbatch equation. Handeison equation for acid; | bH = pka + dog (salt) / Henderson equation for Base; Ipoh = pky + log [salt] [Base] (salt) - concentration of salt Nhyce (Base] concentration of Bease NH3 (Given 0.4490M) Mass of Nhace given a Nrice of 0.7185 g Molar mass of Nhace = 53.5 g/mol Moles of Nigcea mass - Molar mass #moles = 0.7185 g - 53.5 glmole | #moles : 0.0134 mole] Volume of solution - 1.0L Melarity is defined as the number of moles of solute an of sols. Molarity & moles I Volume (AL) / Molarity 2 0.0134 mole Molarity = 0.0134 inde IL i [salt] = 0.0134 m (base] 20.4490 M IL

KG (NH) = 1.80105 pkb = negative logarithm of ke pkg = -logko 3- log (1.88/005) 1 pkb = 4.745] using eqn for base; por pkb it dog (salt) [Base] POH = 4.745+ log 0.0134 O. 4490 pot = 4.745 + log (0.02984) bow - 4.745 +(-1.525) 1. = 4.745-1.525 poh = 3:2197 Now to calculate pH rise PH+POH 14 | TpH = 14-pont PH2 14 -3. 2197 I ÞH = 10.780 / I PH2 10.787 Answer