Question

Calculate and compare the molar solubility of Mg(OH)2 in water and in a solution buffered at a pH of 4.5.

Part 1: (a) Determine the molar solubility of Mg(OH)2 in water and the pH of a saturated Mg(OH)2 solution.

molar solubility =1.39 × 10^-4 M

pH = 10.45

Part 2 out of 3 (b) Determine the molar solubility of Mg(OH)2 in a solution buffered at a pH of 4.5.

molar solubility =_____× 10_____M

Answer 1

Ansher) part) The give Part) The given equation is as follows: - Mg CO₂ (s) mg * (ad) + 2040 (ad) Let the molar solubility of ng COH)₂ = sh .[Mg?] = SM and [OH-] = 251 Solubility product constant ksp can be expressed in terms of concentration as ksp= [ ingat] [on 7² kisma s x (23)2 = 453 We know, Xspling cow) = 109x1ā" Now the solubility produ SX . . The molar solub 2.78x160 = 3.597 x 10" .:53 = Kepa W, 53 = 107x10" iis = (1-388 x10 4 ) " (1.39x109) molar solubility of Mg COH) in water is (1-39x109) M. (Answers :: [on1 = 25M = (2x1-39x104) M = 2.78 x1069M - [ht] = 1x jola = Txiol4 [OH ] We know, pH = -log[ht] = - 10g (3.597 X10'') = 10:44 i pH of the solution is 10.44. (Answers part 2) Now in buffer solution, pH = 4.5 We know, pH tpott = 14 ..pol - 14 - PH = 10-4.5 = 9.5 fr - log [ot] = 9.5 - [ok] = 109.5 :'[OH-] = (3.162 x 10'0) M So, in this buffer solution, Cot] =(3162 x 100) Let the molar solubility of mg (OH)₂ = SM .: [mg2+] = SM. Ksp = [tager] [OH-] ² a, 1*07x16" = Sx (3162 x15 10j2 is = 109 xlo" 2012 = 107 X10" . 9.998 xió 20 ons = (1.0702 x 108)M molar solubility = (1.0702x108) M (Answers