Tutorial 9 Notes - Nov. 20th, 24th Tutorial Notes 1) The...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Nov. 20 th , 24 th Tutorial Notes 1) The solubilities of AgI and Bi 2 S 3 in water are 1.2x10 -8 mol kg -1 and 1.6x10 -20 mol kg -1 respectively, at 25 o C. (Note: The solubility for Bi 2 S 3 previously posted on the website was incorrect.) Calculate their solubility constants. Is there any significant difference when activity coefficients are ignored? (i) The dissociation reaction for silver iodide is: AgI(s) Ag + (aq) + I - (aq) Therefore if the solubility of this salt is 1.2x10 -8 mol kg -1 then the concentration of each ion is: + - 8 -1 Ag 8 I -1 1.2 10 mol kg 1.2 10 1 mol kg o o b b b b ! ! " = = = " . For monovalent salts, the concentration equals the ionic strength of the solution – this can be used to calculate the mean activity coefficient using the limiting law: ( ) Ag I 8 5 log 1 1 0.509 1.2 10 5.58 10 1.0 z z A I ! + " ± " " ± = " = " #" # = " # = Since 1 ± = then: ( ) + - + - Ag I Ag I 2 8 16 1.2 10 1.4 10 sp o o K a a b b b b ! ! = = = " = " Therefore the solubility product for AgI is 1.4x10 -16 and there is no significant difference when the mean activity coefficient is ignored. (ii) The dissociation reaction for Bi 2 S 3 must produce a neutral solution. We know that there are 2 Bi ions and 3 S ions produced in this reaction, although it may not be immediately apparent what the charge number might be. However, if the 2 Bi cations are to be charged balanced by 3 Si ions then 2Bi v+ = 3S v- . The lowest integer values that satisfy this relationship are v + =3, v - =2. From its position on the periodic table we know
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
that S 2- will have a completely filled p-orbital (and is therefore a relatively stable ionization state). Therefore the dissociation reaction is: Bi 2 S 3 (s) 2Bi 3+ (aq) + 3 S 2- (aq) The solubility s = 1.6x10 -20 mol kg -1 . Therefore the concentration of the ions in this solution are: ( ) 3+ 20 -1 20 Bi -1 2 1.6 10 mol kg 2 3.2 10 1 mol kg o o b s b b ! ! " = = = " and
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/22/2011 for the course CHM 2132 taught by Professor Giorgi during the Fall '08 term at University of Ottawa.

Page1 / 6

Tutorial 9 Notes - Nov. 20th, 24th Tutorial Notes 1) The...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online