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Mini review for final

Mini review for final. NB: This does not cover all material!. (very) Rough outline. Units, Conversions , Powers of 10, Prefixes Errors : Sig Figs, Error propagation Statistics: Normal distribution, t-test, Q-test

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Mini review for final

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  1. Mini review for final NB: This does not cover all material!

  2. (very) Rough outline • Units, Conversions, Powers of 10, Prefixes • Errors: Sig Figs, Error propagation • Statistics: Normal distribution, t-test, Q-test • Equilibrium: Constant, Ksp, KH, Kw, separation by precipitation, acids & bases, Ka, Kb • Titration: ve, titration curves • Acid-base titrations

  3. (very) Rough outline • Acids & bases - buffers, HH equation • Electrochemistry Nernst equation ion selective electrode • Spectrophotometry Beer’s Law light, Atomic spectroscopy • Mass spectrometry Isotopes, accurate mass fragmentation • Chromatography – formulas • Other techniques – NMR, XRay, STM

  4. Basic tools Chemical concentrations Molarity = Moles of solute/Liters of Solution (M) Molality = Moles of solute/Kg of Solvent (m) Mole Fraction= Moles solute/total number of moles Mass % = Mass solute/total mass x 100 Volume % = volume solute/total volume x 100 ppm = parts per million * ppb = parts per billion * * mass for solutions, volume for gasses

  5. Basic tools Random error Systematic error

  6. Basic tools significant figure: The number of significant digits in a quantity is the minimum number of digits needed to express the quantity in scientific notation..

  7. Basic tools

  8. Basic tools The real rule: The first uncertain figure is the last significant figure. TIP: In our calculations, we retain extra insignificant digits and round off only at the end.

  9. Basic tools A Gaussian curve in which μ = 0 and σ = 1. A Gaussian curve whose area is unity is called a normal error curve. In this case, the abscissa, x, is equal to z, defined as z = (x − μ)/σ.

  10. Basic tools

  11. Basic tools 0.11/0.2 = 0.55 For 5 measurements Q = 0.65 So…….. KEEP!

  12. calibration (-blanks) Internal standard Standard addition

  13. EQUILIBRIUM NB: K = f(T) K ≠ f(concentrations)

  14. EQUILIBRIUM K IS DIMENSIONLESS! • Concentrations in mol/liter (M) • pressures in atmospheres (atm) • ignore solids • ignore solvents ADD REACTIONS  Multiply Ks REVERSE REACTION  reciprocal K LE CHATELIER’S PRINCIPLE

  15. EQUILIBRIUM SOLUBILITY PRODUCT Ksp COMMON ION EFFECT Ksp = [Ca2+]3[PO43-]2= 1.0 x 10-26 = (3x)3(0.10 + 2x)2 = 1.0 x 10-26 x  solubility (mols/L of Ca3(PO4) that can disolve)

  16. EQUILIBRIUM Gas – solution eaquilibrium KH Henry’s Law CO2 dissolves in water:CO2(g) + H2O <==> H2CO3 (aq) KH = 3.4 x 10-2at a CO2 pressure of 3 x 10-4 atmospheres, what is the concentration of the carbonic acid in the water? H2CO3 <==> H+ + HCO3— Ka = 4.68 x 10-7 What is [H+]? - What is pH?

  17. BrO3¯ EQUILIBRIUM SOLUBILITY PRODUCT Ksp SEPARATION BY PRECIPITATION When (BrO3—) is added to a solution containing equal concentrations of Ag+ and Pb2+, which will precipitate first and why? Ksp = 5.49 x 10-5 for AgBrO3 Ksp = 3.23 x 10-5 for Pb(BrO3)2 Stoichiometry!

  18. TITRATION STEP 1: reaction STOICHIOMETRY! STEP 2: Ve STEP 3: before equivalence what part of analyte is left? STEP 4: at equivalence all analyte consumed STEP 5: after equivalence excess titrant

  19. ACTIVITY

  20. EQUILIBRIUM SOLUBILITY PRODUCTKsp GAS  SOLUTION KH WATER KW ACID Ka BASE Kb PARTITION COEFF. K

  21. EQUILIBRIUM WATER EQUILIBRIUM Kw pH

  22. ACID – BASE EQUILIBRIUM

  23. BUFFERS NB: Equal concentrations  pH = pKa (most effective buffer)

  24. Weak acid With Strong base STEP 1: reaction HA  H+ + A- STEP 2: Ve # mols base added = # mols acid removed

  25. Weak acid With Strong base STEP 3: before equivalence BUFFER! HA  H+ + A- NB: at v = ve/2 concentrations are equal  pH = pKa !

  26. Weak acid With Strong base STEP 3: before equivalence BUFFER! HA  H+ + A- STEP 4: at equivalence A- + H2O  HA + OH- Kb NB: What is pH at equivalence: for titration of strong acid with strong base? and for a weak acid with a strong base > or < 7?

  27. Weak acid With Strong base STEP 3: before equivalence BUFFER! HA  H+ + A- STEP 4: at equivalence A- + H2O  HA + OH- Kb STEP 5: after equivalence excess OH-

  28. Electrochemistry

  29. Electrochemistry How much? – Faraday’s constant. F = (6.022 x 1023 mol-1)x (1.602192 x 10-19 C) = 96,484 C mol-1 Current = Charge/time - I = Q/t [Ampere]=[Coulomb]/[sec]

  30. Electrochemistry

  31. NERNST EQUATION NB: multiplying the Reaction does NOT Change E At 25 oC

  32. NERNST EQUATION

  33. NERNST EQUATION • E= Eo when activities equal 1 • E = 0 at equilibrium

  34. 0.50 M AgNO3(aq) 0.010 M Cd(NO3)2(aq)

  35. Reference electrodes

  36. Ion selective electrode Electrolysis

  37. Spectrophotometry Transmittance Absorbance Beer’s Law

  38. Spectrophotometry • ε depends on • molecule • wavelength

  39. Spectrophotometry λν = c [3 x 108 m/s] E = h ν

  40. Spectrophotometry

  41. Spectrophotometry

  42. Spectrophotometry The fraction of atoms in the excited state is still less than 0.02%, but that fraction has increased by 100(1.74 – 1.67)/1.67 = 4%

  43. Spectrophotometry Linewidth

  44. Mass spectrometry • What is mass 28? • N2 • CO • C2H4 (ethylene) • H6B2 (diborane) http://webbook.nist.gov/chemistry/mw-ser.html

  45. Instrumentation • 3 step program: • Ionize • Mass select • detect • 2. Mass selection: • Magnetic sector • Quadrupole • Time-of-flight (TOF) • Ion trap • Fourier transform ion cyclotron resonance • Ion Mobility NB: REQUIRE VACUUM CHAMBER

  46. Instrumentation – FT-ICR

  47. STEP 1: Ion Source • 70 eV EI • MALDI • ESI

  48. Mass spectrometry • 3 ways to get more out of a mass spectrum: • Isotopes (quantitation) • Exact mass (resolution + accuracy) • Fragmentation (MS/MS)

  49. Mass spectrometry 1. Isotopes What does the mass spectrum of C look like? http://www2.sisweb.com/mstools/isotope.htm

  50. 1. Isotopes What does the mass spectrum of C look like? What does the mass spectrum of C60 look like? Elemental clues from isotope distributions http://www2.sisweb.com/mstools/isotope.htm

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