6/17/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

Did You Know? Problem Set Answers are posted outside the Chemistry Laboratory in a glass case

Problem Set Iron and Barium

Sulfide Precipitation Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

6/17/2015 Soluble Sulfides Na 2 S15.4 (10 °C)1.97 M (NH 4 ) 2 Svery soluble 5460 m H2SH2S18600 (40 °C) 0.34 (100 °C)0.10 M g/100 g H 2 O molar solubility

6/17/2015 Insoluble Sulfides Ag 2 S CdS CoS CuS FeS MnS NiS PbS g/100 g H 2 O 6.4 x x x x x x x x molar solubility 2.6 x x x x x x x x K sp 6.8 x x x x x x x x

6/17/2015 Preparation of Hydrogen Sulfide (acidic solution) 2 H + (aq) + S 2– (aq) H 2 S(aq) H H C H H H C N S      + H 2 O(l) H 2 S(aq) thioacetamide An aqueous solution H 2 S of is called hydrosulfuric acid

6/17/2015 Preparation of Sulfide Ion (basic solution) H 2 S(aq) + 2 OH – (aq) S 2– (aq) + 2 H 2 O(l) 0.1 M Na 2 S [S 2– ] = 5.0 x 10 –2 M 0.1 M (NH 4 ) 2 S [S 2– ] = 2.0 x 10 –5 M Write the reaction of aqueous ammonia and hydrosulfuric acid to give sulfide ion.

6/17/2015 Reactions of Hydrosulfuric Acid (polyprotic acid) 2 H + (aq) + S 2– (aq) H 2 S(aq) H + (aq) + HS – (aq) H 2 S(aq) H + (aq) + S 2– (aq) HS – (aq) hydrosulfuric acid.bisulfide ion sulfide ion

6/17/2015 First Dissociation of H 2 S H + (aq) + HS – (aq) H 2 S(aq) [H + ] [HS – ] [H 2 S] = K 1 = 1.0 x 10 –7 M 1 indicates it is the ionization of the first hydrogen ion Also called K a,1

6/17/2015 H + (aq) + S 2– (aq) HS – (aq) Second Dissociation of H 2 S [H + ] [S 2– ] [HS – ] = K 2 = 1.3 x 10 –13 M

6/17/ H + (aq) + S 2– (aq) H 2 S(aq) Double Dissociation of H 2 S [H + ] 2 [S 2– ] [H 2 S] = K 12 = K 1  K 2 =1.3 x 10 –20 M 2 This equilibrium constant can be used for any sulfide ion and pH calculation at room temperature

6/17/2015 Dissociation of Hydrosulfuric Acid H + (aq) + HS – (aq) H 2 S(aq)2 H + (aq) + S 2 – (aq) very acidicneutralvery basic The solubility of H 2 S in water decreases with increasing temperature. The amount of sulfide ion in solution is pH dependent.

Thioacetamide is heated in boiling water for 5 minutes Determine the concentration of the other sulfur containing species [H 2 S] = 0.10 M pH = 1.0pH = 5.0pH = 9.0

6/17/2015 The Effect of pH on the Sulfide Ion Concentration pH[H + ] [S 2– ] M 10 –1 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 10 –8 10 –9 1.3 x 10 –21 M 1.3 x 10 – x 10 – x 10 – x 10 – x 10 – x 10 –9 1.3 x 10 –7 1.3 x 10 –5 1.3 x 10 –3

6/17/2015 What would a graph of the various sulfide containing species versus pH look like? pH  Mole Fraction acidicbasic H2SH2S HS – S2–S2– Excel Graph

6/17/ M Silver Ion Solution If the concentration of H 2 S in the aqueous solution is 0.10 M, what will be the pH of the solution whenpH silver sulfide begins to precipitate? What sulfide ion concentration issulfide ion needed to precipitate silver sulfide?

6/17/ M Silver Ion Solution [Ag + ] 2 [S 2– ] = K sp [S 2– ] = K sp [Ag + ] x 10 –50 M 3 (0.1 M) 2 = 6.8 x 10 –48 M =

6/17/2015 [H + ] 2 [S 2– ] [H 2 S] = K 12 = 1.3 x 10 –20 M M Silver Ion Solution [S 2– ] = 6.8 x 10 –48 M [H + ] 2 (6.8 x 10 –48 M) [H 2 S] 0.10 M Remember this equilibrium constant? It can be used for any sulfide ion and pH calculation [H + ] = 1.4 x M pH = -13.1

6/17/2015 An aqueous solution contains 0.1 M concentrations of the following ions Ag +, Cd 2+, Co 2+, Cu 2+, Fe 2+, Mn 2+, Ni 2+, Pb 2+ In what order will these ions precipitate when sulfide is added to the solution? If the H 2 S concentration is 0.10 M, at what pH will each ion begin to precipitate? Select a +2 metal ion (0.1 M) and calculate the pH at which the metal sulfide of that ion will begin to precipitate.

6/17/2015 Sulfide Precipitation Values Ion 0.1 M Ag M Cd M Co M Cu M Fe M Mn M Ni M Pb 2+ [S 2– ] Required 6.8 x 10 –48 M 1.0 x 10 –27 M 5.0 x 10 –21 M 8.7 x 10 –35 M 4.9 x 10 –17 M 5.1 x 10 –14 M 3.0 x 10 –20 M 4.2 x 10 –27 M [H + ] 1.4 x M 1.1 x 10 3 M 5.1 x 10 –1 M 3.9 x 10 6 M 5.2 x 10 –3 M 1.6 x 10 –4 M 2.1 x 10 –1 M 5.6 x 10 2 M pH

6/17/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

Problem Set Sulfide Precipitation Reactions

6/17/2015 Selective Precipitation pH basic neutral acidic very acidic  FeS  MnS some metal sulfides can be easily dissolved  CoS  NiS some metal sulfides require concentrated acids to dissolve  CdS  PbS some metal sulfides require concentrated acids and special ligands to dissolve  CuS Ag 2 S some metal sulfides will not dissolve, but can only be destroyed with nitric acid

6/17/2015 Sulfide Ion Precipitation A solution has the following composition 10 drops 0.10 M Ni drops 0.10 M Pb drops 0.10 M Cu drops thioacetamide 2 drops 6 M HCl 20 drops water What is the concentration of each cation?

6/17/2015 Sulfide Ion Precipitation 10 drops 0.10 M Ni drops 0.10 M Pb drops 0.10 M Cu drops thioacetamide 2 drops 6 M HCl 20 drops water 50 drops total volume

6/17/2015 Cation Concentrations [Ni 2 + ] =x 0.10 M 10 drops 50 drops [Pb 2 + ] =x 0.10 M = M 10 drops 50 drops [Cu 2 + ] =x 0.10 M = M 2 drops 50 drops [H + ] =x 6.0 M = 0.24 M 2 drops 50 drops = M

6/17/2015 Sulfide Ion Generation The solution is boiled for 5 minutes to generate a saturated H 2 S solution. What is the concentration of sulfide ion in this solution, if [H + ] = 0.24 M?

6/17/2015 Sulfide Ion Generation [H 2 S] = 2 H + (aq) + S 2– (aq) H 2 S(aq) [H + ] 2 [S 2– ] [H 2 S] = K 12 = 1.3 x 10 –20 M 2 H 2 S(aq) H 2 S(g) from thioacetamide decomposition 0.10 M

6/17/2015 Sulfide Ion Generation [H 2 S] = 0.10 M [H + ] = 0.24 M [S 2– ] = 2.3 x 10 –20 M H 2 S(aq) H 2 S(g)

6/17/2015 Which of the metal ions remain in solution and which precipitate? Ni 2+, Pb 2+, Cu 2+ 2 drops 6 M HCl thioacetamide

6/17/2015 Which of the metal ions remain in solution and which precipitate? NiS: K sp, NiS = 3.0 x 10 –21 M 2 Ni 2+ in solution [Ni 2 + ] [S 2– ]= (0.020)(2.3 x 10 –20 )= 4.6 x 10 –22 M 2 Determine if lead(II) ion will precipitate or remain in solution. This is what we have This is the solubility limit compare these

6/17/2015 Which of the metal ions remain in solution and which precipitate? PbS: K sp, PbS = 4.2 x 10 –28 M 2 PbS precipitates [Pb 2 + ] [S 2– ]= (0.020)(2.3 x 10 –20 )= 4.6 x 10 –22 M 2 < 4.6 x 10 –22 M 2 Determine if copper(II) ion will precipitate or remain in solution.

6/17/2015 Which of the metal ions remain in solution and which precipitate? CuS: K sp, CuS = 8.7 x 10 –36 M 2 CuS precipitates [Cu 2 + ] [S 2– ]= (0.004)(2.3 x 10 –20 )= 9 x 10 –23 M 2 < 9 x 10 –23 M 2

6/17/2015 Which of the metal ions remain in solution and which precipitate? PbS, CuS Ni 2+, Pb 2+, Cu 2+ 2 drops 6 M HCl thioacetamide Ni 2+

6/17/2015 Metal Sulfide Dissolution Reactions  Sulfuric Acid The acidity of the solution will determine if the metal sulfide will dissolve. FeS(s) + 2 H + (aq) Fe 2+ (aq) + H 2 S(g) Sulfate ion is a poor coordinating ligand, and does not assist in the dissolution process. Hydrogen sulfide gas is released if the metal sulfide dissolves.

6/17/2015 Metal Sulfide Dissolution Reactions  Hydrochloric Acid HCl will dissolve a few metal sulfides that sulfuric acid does not dissolve. Chloride ion coordinates to the metal ion to form a more soluble complex anion. Hydrogen sulfide gas is released if the metal sulfide dissolves.

6/17/2015 Metal Sulfide Dissolution Reactions  Hydrochloric Acid CdS(s) + 2 H + (aq) + 4 Cl – (aq) [CdCl 4 ] 2– + H 2 S(g) tetrachlorocadmate ion ? Cadmium sulfide will not dissolve in 6 M sulfuric acid but will dissolve in 6 M hydrochloric acid

6/17/2015 Metal Sulfide Dissolution Reactions  Nitric Acid All metal sulfides dissolve in warm nitric acid. The nitrate ion is an oxidizing agent which oxidizes sulfide ion (S 2– ) to white elemental sulfur (S). During the redox process, nitrate ion is reduced to NO 2 gas, or in the case of nickel to NO gas.

6/17/2015 Metal Sulfide Dissolution Reactions Nitric Acid Ag 2 S(s) + H + (aq) + NO 3 – (aq) Ag + (aq) + NO 2 (g) + H 2 O(l) + S(s) Ag 2 S(s)2 Ag + (aq) NO 3 – (aq)NO 2 (g)2 H + (aq) +e– +e– ++ H 2 O(l) + S(s)+ 2 e – Balance this redox equation in acidic solution

6/17/2015 End of Part 1 Be sure to review the Exam I Objective Sheet

The organization of the elements by Moseley is accepted as being superior to that of the Meyer and Mendeleev. In which of the following ways is it the most superior? Prediction of missing elements Prediction of elemental properties Prediction of compounds formed with hydrogen and oxygen

Write a balanced and completely annotated (g,s,l,aq) chemical net ionic equation for the reaction of diamminesilver ion with hydrochloric acid to give insoluble silver chloride. Ag(NH 3 ) H + (aq) + Cl – (aq) AgCl(s) + 2 NH 4 + (aq)

6/17/2015 Which of the following is the most basic? 5 M HCl aqueous solution with a pH of 6 aqueous solution with [OH – ] = 1 x 10 –12 M Next 5 M HCl aqueous solution with a pH of 6 aqueous solution with [OH – ] = 1 x 10 –12 M

6/17/2015 An aqueous solution contains 0.1 M Cd 2+ and 0.1 M Cu 2+ Ksp cadmium hydroxide2.0 x 10 –14 copper(II) hydroxide1.6 x 10 –19 Cd(OH) 2 Cu(OH) 2 Next If the solution is slowly made basic, what will be the formula of the first precipitate to form? Cu(OH) 2

6/17/2015

One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes