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BU CHEM 108 - Exam 3 Study guide
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Chem 108 1st editionExam #3 Study GuideChapter 16: Acids and BasesTitration of a polyprotic acid:- Polyprotic acid: are able to donate more than one proton per acid molecule. - There is are equivalence points for each proton o H2CO3 has two equivalence pointso H3PO4 has three equivalence points- It is hard to distinguish equivalence points if Ka1 and Ka2 are close to one another, which means the titration will work if the Ka values are about 104 apart - Example: The titration of H2CO3o 15 ml H2CO3 titrated to and point with 40 ml of 0.25 M NaOH. Calculate for concentration H2CO3.o NaOH + H2CO3 → NaHCO3 + H2O NaOH + NaHCO3 → Na2CO3 + H2O Add these up: 2NaOH + H2CO3 → Na2CO3 + 2H2O 2mol of NaOH react with 1mol H2CO3o Mol Acid/Mol base = Conc acid * Volume acid/ Conc base * vol base(nA /nB)=(VAMA)/(VBMB)o 1/2 = (Conc acid * 15)/(0.25*40)o Conc acid = 0.25*40/30 o Conc acid = 10/30 = 0.33MChapter 17 Complex Ions:Complex ion: - Complex ion: ionic species consisting of a metal cation bond to one or more Lewis bases- Coordinate bond: bond formed when one anion/molecule, donates a pair of electrons to another ion/molecule to form a covalent bond.- Ligands: a Lewis base bonded to the central metal ion of a complex ion.o Lewis base: a substance that donates a lone pair of electrons. o Common ligands: NH3, H2O, OH-, Cl-, CN-- Inner coordination sphere: ligands that are bound directly to a metal via coordinate covalent bonds.- Counter Ions: Ions that balance the electrical charges of complex ions in coordination compounds- Coordination Compound: any compound that contains a complex ion- Coordination number: Identifies the number of electron pairs surrounding a metal ion in acomplexo Common Coordination numbers and shapes for complex ions:o Coordination # o Shape o Exampleso 6 o Octahedral o Fe(H2O)62+o 4 o Tetrahedral o Zn(NH3)42+o 4 o Square planar o Pt(NH3)42+o 2 o linear o Ag(NH3)2+Shape of complex ions: - Depends on the number of ligands surrounding the central metal cationo Example: Zn(NH3)42+ Zn2+: [Ar] 3d10 (4s and 4p orbitals empty)o S and p orbitals mix to form four sp2 hybridized orbitals o NH3: electron pair donors, form four coordinate covalent bonds = tetrahedral - Ligands donate electron pairs to empty orbitalsNaming Complex ions:1. Name the ligands first in alphabetical order using di(2),tri(3) or tetra(4) if neededAnionic LigandsNames Neutral Ligands NamesBr-bromo NH3ammineF-fluoro H2O aquaO2-oxo NO NitrosylOH-Hydroxo CO CarbonylCN-cyano O2dioxygenC2O42-oxalato N2dinitrogenCO32-carbonato C5H5N pyridine2. Write the name of the transition metal ion with a Roman numeral indicating the oxidation state. If negative charged complex ion add –ate to the nameo Fe(H2O)6 2+ Hexaaquairon (II)Steps for a positively charged complex ion:1. Add-ate ending to the name of the central metal ion to indicate that complex ion carries a negative ion.o Fe(CN)63- Hexacyanoferrate(III)Name of Metal Name in an Anionic ComplexIron FerrateCopper CuprateLead PlumbateSilver ArgenateGold AurateTin Stannate2. If counter ion is cation, name cation first, followed by name o anionic complex iono K3[Fe(CN)63- ] Potassium Hexacyanoferrate(III)3. If counter ion is an anion, name cationic complex ion first, followed by name of anion.o [Ni(NH3)6]Cl2 Hexaamminenickel (II) chloride Solubilities of Hydrated Complex Ions:- Most transition metal cations form insoluble hydroxides: o Fe(OH)3 (s) ⇌ Fe3+ (aq) + 3OH− (aq) Ksp = 1.1 × 10−36 o Al(OH)3 (s) ⇌ Al3+ (s) + 3OH− (aq) Ksp = 1.9 × 10−33 - For some, solubility increases in strongly basic solution: o Al(OH)3 (s) + OH− (aq) ⇌ Al(OH)4 − (aq) [Al(H2O)2 (OH)4 ] – o Cr(OH)3 (s) + OH− (aq) ⇌ Cr(OH)4 − (aq) [Cr(H2O)2 (OH)4 ] −Polydentate Ligands: - Monodentate ligand: Species that forms a single coordinate bond to a metal ion in a complex (NH3 , Cl− ). - Polydentate ligand: Species that can form more than one coordinate bond per molecule. - Chelation: Interaction of a metal ion with a ligand having multiple donor atoms (chelating agent).Ligand Displacement: - Ligands with a higher affinity for metal cation will displace ligands with less affinity- Ni(H2O)62+ + 6NH3 ⇌ Ni(NH3)6 2+ + 6H2O o Kf = 5 × 108 NH3 is a stronger Lewis base than H2O- When Ligands get replaced the colors of the complex ion change as well. - Chelate Effect: Greater affinity of metal ions for polydentate ligands than for monodentate ligands. o Ni(NH3)6 2+ + 3en ⇌ Ni(en)32+ + 6NH3 o Kf = 1.1 × 1018 o This is an Entropy-driven processCrystal Field Theory: - Crystal field splitting: Process of changing degenerate d-orbitals (same energy) into subsets with different energies as a result of interactions between electrons in those orbitals and lone pairs of electrons in ligands. - Crystal field splitting energy (Δ): The difference in energy between subsets of d orbitals split by interactions in a crystal field.- This also explains the color change when the ligands displace another ligand in a complex ionColor of complex Ion:- Color observed is complementary (opposite) of color of absorbed light.o Red is complementary to greeno Orange is complementary to Blueo Yellow is complementary to violet - This also depends on the wavelength of light that the complex ion absorbso Red has the lowest wavelength, and violet has the highest wavelength Spectrochemical Series: - Rank-ordering of ligands based on their ability to split d-orbital energies.- (weak-field ligands) I- < Br- < SCN- < Cl- < F- ≤ OH- , ONO- < OH2 < NCS- < NCCH3 < NH3 , py < NO2- < CN- , NO , CO (strong-field ligands)- Field strength is created by the repulsion force of the ligand with the central-ion electrons.- Crystal field splitting energy (Δ) increases as field strength increases.- High field strength ligands form complexes that absorb short wavelength, high energy light. - Low field strength ligands absorb long wavelength low energy light.Magnetic Properties:- Paramagnetism: Attraction to magnetic field; requires unpaired electrons. The more unpaired electrons the more paramagnetic. - High-spin state: Low field strength = small Δ. Maximize unpaired electrons. o Ex: five unpaired electrons- Low-spin state: High field strength = large Δ. Minimize unpaired electrons.o Ex: one unpaired electron- For Octaheral shaped complexes if the ligand has high field strength then it is in low spin state. But if the ligand has low field strength then it is in high spin


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BU CHEM 108 - Exam 3 Study guide

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