Print version. Lecture #26 Coordination Chemistry: Hydrolysis. Benjamin; Chapter (Stumm & Morgan, Chapt.6: pg ) Updated: 22 March 2018

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1 Updated: 22 March 2018 Print version Lecture #26 Coordination Chemistry: Hydrolysis (Stumm & Morgan, Chapt.6: pg ) Benjamin; Chapter David Reckhow CEE 680 #26 1

2 From Lecture #20 Acid Titration Curve for a Water Containing Hydroxide and Carbonate Alkalinity ph H + +OH - =H 2 O 1 st Equivalence Point 2 nd Equivalence Point H + +CO 3-2 =HCO3 - Α A Titrant Volume (ml) David Reckhow CEE 680 #20 2 B Β H + +HCO 3 - =H2 CO 3 V ph Vmo

3 From Lecture #20 Acid Titration Curve for a Water Containing Carbonate and Bicarbonate Alkalinity ph Α Y[CO 3-2 ] + Z[HCO3 - ] 1 st Equivalence Point (Y + Z)[HCO 3 - ] 2 nd Equivalence Point (Y)V s /N t (Y + Z)V s /N t V ph V mo Titrant Volume (ml) David Reckhow CEE 680 #20 3 Β C (Y + Z)[H 2 CO 3 ]

4 From Lecture #17 Buffer Intensity Amount of strong acid or base required to cause a specific small shift in ph β = dcb dph dca = dph ph David Reckhow CEE 680 #17 f Starting Point ph g Mid-point ph 4.7 C B M HAc 0.2 End Point ph 8.35 ph 0.0 C B ph Slope = 1/β -0.2

5 Base titration of an acid For a monoprotic Lecture #16 C B [Na + ] = [A - ] + [OH - ] - [H + ] For a diprotic Using the same ENE approach f VBN = V M s [ A = B [ OH = α + 1 s equb = moles ] + [ OH C T T s ] [ H ] [ H C C = C + ] + B T ] ff = 2 AA 2 + HHHH + OOOO + HH + CC TT ff = 2αα 2 + αα 1 + OOOO + HH + 2 [ + ] [ ] H H [ H ] K2 K + 1 1K2 K K HH [ H ] + 1 David Reckhow KK aa CEE 680 # CC TT

6 Example Titration Base titration V s = 1000 ml M s = M N B = 0.1 M Starting acids Pure water 1 mm HAc 1 mm H 2 CO 3 V N V M B B f = = s s equb moles ph i = 3.85 pk a =?? pk as =?? s David Reckhow CEE 680 #26 6

7 Titration of Humics From Lecture #18 Model for aquatic humic substances Acetic acid + phenol David Reckhow CEE 680 #18 7

8 Protons & Metals Ions Why?? Fig 6.2 pg.259 David Reckhow CEE 680 #26 8

9 Complexation of hydroxide? No Yes, a bit Yes, quite a bit David Reckhow CEE 680 #2 9

10 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 10

11 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 11

12 Intro: Coordinative Reactions Definition: where the coordination number or coordination partner changes Types Acid/base reactions HClO = H + + ClO - Precipitation reactions HClO + H 2 O = H 3 O + + ClO - Mg OH - = Mg(OH) 2(s) Complexation reactions Cu NH 3 = Cu(NH 3 ) 4 +2 Mg(H 2 O) OH - = Mg(OH) 2(s) + 2H 2 O Cu(H 2 O) NH 3 = Cu(NH 3 ) H 2 O David Reckhow CEE 680 #26 12

13 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 13

14 Coordination Definition Any combining of cations with molecules or anions containing free pairs of electrons Complex or Coordination Compound Central atom Cu NH 3 = Cu(NH 3 ) 4 +2 Ligand atom Ligand H N H H David Reckhow CEE 680 #26 14

15 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) Three: tridentate (e.g., citrate) Six: hexadentate (e.g., EDTA) Multidentate Resulting complexes are called chelates David Reckhow CEE 680 #26 15

16 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 16

17 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 17

18 Ion pair stability Determined based on simple coulombic interactions Ion Log K Log K Charge (I=0) (seawater) 1 0 to to to to to 4.0 David Reckhow CEE 680 #26 18

19 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 - M + O-M David Reckhow CEE 680 #26 19

20 Chemical Speciation David Reckhow CEE 680 #26 Fig 6.1, pg

21 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 21

22 Fig 6.3 Pg.259 Cu(NH 3 ) X David Reckhow CEE 680 #26 22

23 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 23

24 Complexes: Coordination # Me(Ligand) x Fe(H 2 O) 6 +3 Fe(H 2 O) 4 (OH) 2 +1 PtCl 6-2 Cu(NH 3 ) 4 +2 Si(OH) 4 HgS 2-2 HOH 2 Coordination Number 4 6 Coordination # Depends on: 1. Size of central Atom 2. Charge of central Atom 3. Size of Ligand David Reckhow CEE 680 #26 24

25 To next lecture David Reckhow CEE 680 #26 25