Question

Consider a saturated solution of La(OH)3 in 0.10 M KNO3 at 25 °C. For La(OH)3, Ksp = 2.0 x 10-21. Including activities, calculate the concentration of lanthanum ions What is the pH in this saturated solution? Again, include activities. Why is the answer in part (b) still not the pH you'd measure for an actual saturated solution of lanthanum hydroxide?!

Answer 1

as complete 2 10 auteurine Solubility of spasungly Soluble sat, we Did Leum that is Solubility -> Subhoge , solubility pecadend lksp] ability of a sparingly of a sparingly soluble Solu Suet , scy 13. (s) mole per titre. Since ito' Concentration will beouts man, it may be taken cui nouilled Suthod unrent nation of both sliver and chloride ion will be (s) mole per litre each. -) solubility product ksp of silver chloride is given by it ký : [ Cur] - sº , most important expression use to solve further part of auestion. La (OH)3. & Csatlated Lapte + 3 oH s 35 Soin) can) ) concentration 2034 is 1ST - ) where as long as where as for Jis som ksp = = =) - = [kq3t] [orijs [5] [35] s * 2753 5427 975" KSP root both the side KSP 21 Taking quatrat So, ean becomes to be now, ilue of ksp = ax 1021 (kopply = 5 - a Putting value in ear cs Scanned with ETH

We get, 2x10- 27 Takin both the side end aus. net! enve from erer! cran 21 301 ave ( 7,0 coni. H. 5s long (2015) "* - tongos) dorg (4)= a.- - t dog a Pak.) - log(s) loge logenin). log ni duss = log (2x1071) - log(37) - logls) =) [ clog at dog 1071 - loga 7] wgs -) to [ loga + -21 log 10 log st] = logs. a t s log 2 + (-dilxl - log at] - logs =) to [ 0.3010 -21 - 11431 ] = log s =) to [0:3010 -22.431] = logs -22:13.J= logs =) -5,5325 = dogrs) again rearranging =) S= Anbilogl-5.5325] som 13 = 2.9x1000) = concentration of 2031 ion is Is 9 x106] =) where as concentration of of ion is= 13XS/ =) 342.4x100 =) 18.7x/0+ 0 we set antilog. cs) Scanned with CamScanner

POH JR: ☺ POH = -log Cow-] we know POH = -log[ 8.98165]. pOH = flog (9.7) + log (1-6)] poh - flog (8-7) -6] Por = -[ 0.9395 + ] pot = -0.939 5 + 6 pot = 5.0605 | we abo know that, TPH + POH = 14 PH = 14 - POH PH - 14 -5.0605 T? H = 8:9 3 4 5 | Simon Lanthanum hydroxide is a slowingly soluble Sull, so, 'it dissolve in mau Ommount. As (PH) of Solution will be according to the concentration of hydroxide ion in the Solution And un dissolved salt will remain in the form of precipitate in the solution Fics Scanned with CamScanner