CEE 680 Lecture #26 3/4/2020 Print version Updated: 4 March 2020 - PDF document

CEE 680 Lecture #26 3/4/2020 Print version Updated: 4 March 2020 Lecture #26 Coordination Chemistry: Hydrolysis (Stumm & Morgan, Chapt.6: pg.260 ‐ 271) Benjamin; Chapter 8.1 ‐ 8.6 David Reckhow CEE 680 #26 1 Acid Titration Curve for a Water Containing Hydroxide and Carbonate Alkalinity 12 + - H + O H = H O 2 11 H++CO3 -2=HCO3 - 10 9 B From Lecture #20 1 st Equivalence Point  8 A H++HCO3 pH 7  -=H2CO3 6 2 nd Equivalence Point 5 4 3 V ph V mo 2 0 5 10 15 20 25 30 35 40 45 Titrant Volume (mL) David Reckhow CEE 680 #20 2 1

CEE 680 Lecture #26 3/4/2020 Acid Titration Curve for a Water Containing Carbonate and Bicarbonate Alkalinity 12 -2] + Z[HCO3 -] Y[CO3 11 10 C From Lecture #20 9 1 st Equivalence Point  -] 8 (Y + Z)[HCO3 pH 7  6 (Y + Z)[H2CO3] 2 nd Equivalence Point 5 4 (Y + Z)Vs/Nt (Y)Vs/Nt 3 V ph V mo 2 0 5 10 15 20 25 30 35 40 45 Titrant Volume (mL) David Reckhow CEE 680 #20 3 10 -2 M HAc Buffer Intensity g  Amount of strong 1 .2 1 .0 0 .8 0 .6 0 .4 0 .2 0 .0 -0 .2 1 2 acid or base 1 1 From Lecture #17 required to cause a M id -p o in t 1 0 specific small shift p H 4 .7 9 in pH S ta rtin g P o in t 8 p H 3 .3 5 E n d P o in t pH 7  p H 8 .3 5 pH dC dC 6     B A  C B 5 dpH dpH  pH  4 C B 3 Slope = 1/  2 -0 .2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 f David Reckhow CEE 680 #17 4 2

CEE 680 Lecture #26 3/4/2020 Base titration of an acid  For a monoprotic  For a diprotic  Lecture #16  Using the same ENE  C B  [Na + ] = [A ‐ ] + [OH ‐ ] ‐ [H + ] approach 𝑔 � 2 𝐵 �� � 𝐼𝐵 � � 𝑃𝐼 � � 𝐼 � V N equ C    f B B B B 𝐷 � V M moles C s s s T      [ A ] [ OH ] [ H ]  𝑔 � 2 𝛽 � � 𝛽 � � 𝑃𝐼 � � 𝐼 � C T 𝐷 �    [ OH ] [ H ]    1 C T 1 1  1   2   [ H ]   K [ H ] [ H ] 1 1 2 K  K K K 𝐼 � [ H ] 1 1 2 2 𝐿 � � 1 David Reckhow CEE 680 #26 5 Example Titration  Base titration  V s = 1000 mL V N equ   B B B f  M s = 0.001 M V M moles s s s  N B = 0.1 M  Starting acids  Pure water  1 mM HAc pH i = 3.85 pK a = ??  1 mM H 2 CO 3 pK as = ?? David Reckhow CEE 680 #26 6 3

CEE 680 Lecture #26 3/4/2020 Titration of Humics  Model for aquatic humic From Lecture #18 substances  Acetic acid + phenol David Reckhow CEE 680 #18 7 Protons & Metals Ions  Why?? Fig 6.2 pg.259 David Reckhow CEE 680 #26 8 4

CEE 680 Lecture #26 3/4/2020 +2 FeOH(H 2 O) 5 Fe O H David Reckhow CEE 680 #28 9 + Fe(OH) 2 (H 2 O) 4 H O Fe O H David Reckhow CEE 680 #28 10 5

CEE 680 Lecture #26 3/4/2020 Limits to Growth  Lake Taihu C 106 H 263 O 110 N 16 P NO 3 - CO 2 H 2 O HPO 4 -2 David Reckhow CEE 680 #25 11 Another Problem Statement  Photosynthesis with nitrate assimilation ‐ + HPO 4 ‐ 2 + 122 H 2 O + 18 H +  106 CO 2 + 16 NO 3 = C 106 H 263 O 110 N 16 P + 138 O 2  Basis for stoichiometry and limits to growth  Algal cells are: C 106 H 263 O 110 N 16 P  But what if they are: C 106 H 263 O 110 N 16 P 1 Fe 0.001 David Reckhow CEE 680 #25 12 6

CEE 680 Lecture #26 3/4/2020  O Elemental abundance in crust  Si  Al  Fe  Ca  Na  Mg  K  Ti  H  P  Mn  F David Reckhow CEE 680 #2 13 Elemental abundance in fresh water From: Stumm & Morgan, 1996; Benjamin, 2002; fig 1.1 David Reckhow CEE 680 #2 14 7

CEE 680 Lecture #26 3/4/2020 Complexation of hydroxide? No Yes, a bit Yes, quite a bit David Reckhow CEE 680 #2 15 Precipitation and Dissolution  Environmental Significance  Engineered systems  coagulation, softening, removal of heavy metals  Natural systems  composition of natural waters  formation and composition of aquatic sediments  global cycling of elements  Composition of natural waters  S&M, 3rd ed., figure 15.1 (pg. 873) David Reckhow CEE 680 #26 16 8

CEE 680 Lecture #26 3/4/2020 Intro: Chemical Reactions  Driving force  Reactants strive to improve the stability of their electron configurations (i.e., lower  G)  Types  Redox reactions: change in oxidation state  Coordinative reactions: change in coordinative relationships David Reckhow CEE 680 #26 17 Intro: Coordinative Reactions  Definition: where the coordination number or coordination partner changes  Types  Acid/base reactions HClO = H + + ClO - HClO + H 2 O = H 3 O + + ClO -  Precipitation reactions +2 + 2OH - = Mg(OH) 2(s) Mg +2 + 2OH - = Mg(OH) 2(s) Mg(H 2 O) 2 + 2H 2 O  Complexation reactions +2 + 4NH 3 = Cu(NH 3 ) 4 Cu(H 2 O) 4 +2 Cu +2 + 4NH 3 = Cu(NH 3 ) 4 +2 + 4H 2 O David Reckhow CEE 680 #26 18 9

CEE 680 Lecture #26 3/4/2020 Coordination Chemistry: References  Benjamin, 2002: Chapt. 8  Appendix A4  Stumm & Morgan, 1996: Chapt. 6  Butler, 1998: Chapt. 7 & 8  Pankow, 1991: Chapt. 18  Langmuir, 1997: Chapt. 3  Snoeyink & Jenkins, 1980: Chapt. 5  Morel & Hering, 1993: Chapt. 6  Morel, 1983: Chapt. 6  Buffle, 1988: Chapt. 5 & 6 David Reckhow CEE 680 #26 19 Coordination  Definition  Any combining of cations with molecules or anions containing free pairs of electrons Complex or Coordination Compound Cu +2 + 4NH 3 = Cu(NH 3 ) 4 +2 Ligand atom Central atom Ligand N H H H David Reckhow CEE 680 #26 20 10

CEE 680 Lecture #26 3/4/2020 Ligand types  Constituent Ligand atoms  Nitrogen  Oxygen  Others: halides  Numbers of active ligand atoms per ligand  One: monodentate (e.g., ammonia)  Two: bidentate (e.g., oxalate) Multidentate  Three: tridentate (e.g., citrate) Resulting complexes  Six: hexadentate (e.g., EDTA) are called chelates David Reckhow CEE 680 #26 21 Coordination Basics  Importance  Affects solubility of metals  e.g., Al(OH) 3 solubility  Used in Analytical chemistry  Determination of hardness  Metals act as buffers in natural waters  Coordination Number  1 for Hydrogen  2, 4, or 6 for most metals David Reckhow CEE 680 #26 22 11

CEE 680 Lecture #26 3/4/2020 Ion Pairs & Complexes  Two types of complex species  Ion Pairs  Ions of opposite charge that form an association of lesser charge  Ion pairs are separated by at least one water molecule  These are called “outer ‐ sphere” complexes  Complexes  Metal ion and neutral or anionic ligand  Direct bond formed with no water molecule between  These are called “inner ‐ sphere” complexes David Reckhow CEE 680 #26 23 Ion pair stability  Determined based on simple coulombic interactions Ion Log K Log K Charge (I=0) (seawater) 1 0 to 1 -0.5 to 0.5 2 1.5 to 2.4 0.1 to 1.2 3 2.8 to 4.0 David Reckhow CEE 680 #26 24 12

CEE 680 Lecture #26 3/4/2020 Natural Particle as Ligands  Natural Particles  High surface area  Usually coated with oxygen ‐ containing surface groups which can donate electrons to metals (i.e., act as ligands) S S S OH O - O-M M + David Reckhow CEE 680 #26 25 Chemical Speciation Fig 6.1, pg. 258 David Reckhow CEE 680 #26 26 13

CEE 680 Lecture #26 3/4/2020 Protons & Metals Ions  All “free” metals and protons are actually hydrated in water  Both can bind with hydroxide Fig 6.2 pg.259 David Reckhow CEE 680 #26 27 Cu(NH 3 ) X Fig 6.3 Pg.259 David Reckhow CEE 680 #26 28 14

CEE 680 Lecture #26 3/4/2020 Brønsted & Lewis Acidity  Definition of Acids  Brønsted: proton donors  Species with excess H +  Lewis: electron acceptors  H + , metal ions, others  Strength  Tendency to accept electrons (or donate protons)  Measured by equilibrium constant David Reckhow CEE 680 #26 29 Complexes: Coordination #  Me(Ligand) x Coordination Number +3  Fe(H 2 O) 6 6 +1  Fe(H 2 O) 4 (OH) 2 ‐ 2  PtCl 6 +2  Cu(NH 3 ) 4 4  Si(OH) 4 Coordination # Depends on: ‐ 2  HgS 2 2 1. Size of central Atom  HOH 2. Charge of central Atom 3. Size of Ligand David Reckhow CEE 680 #26 30 15

CEE 680 Lecture #26 3/4/2020  To next lecture David Reckhow CEE 680 #26 31 16