Mini review for final

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Jemimah McCormick
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1 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 Equilibrium: Constant, K sp, K H, K w, separation by precipitation, acids & bases, K a, K b Titration: v e, titration curves Acid-base titrations (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 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 1

2 Basic tools 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.. Random error Systematic error Basic tools 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. 2

3 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. Basic tools Basic tools calibration (-blanks) Internal standard 0.11/0.2 = 0.55 For 5 measurements Q = 0.65 So.. KEEP! Standard addition 3

4 EQUILIBRIUM EQUILIBRIUM K IS DIMENSIONLESS! Concentrations in mol/liter (M) pressures in atmospheres (atm) ignore solids ignore solvents NB: K = f(t) K f(concentrations) REVERSE REACTION reciprocal K ADD REACTIONS Multiply Ks LE CHATELIER S PRINCIPLE EQUILIBRIUM SOLUBILITY PRODUCT Ksp COMMON ION EFFECT EQUILIBRIUM Gas solution eaquilibrium K H Henry s Law CO 2 dissolves in water: CO 2 (g) + H 2 O <==> H 2 CO 3 (aq) K H = 3.4 x 10-2 Ksp = [Ca 2+ ] 3 [PO 4 3- ] 2 = 1.0 x = (3x) 3 ( x) 2 = 1.0 x at a CO 2 pressure of 3 x 10-4 atmospheres, what is the concentration of the carbonic acid in the water? H 2 CO 3 <==> H + + HCO 3 Ka = 4.68 x 10-7 x solubility (mols/l of Ca 3 (PO 4 ) that can disolve) What is [H + ]? - What is ph? 4

what part of analyte is left? Ksp = 5.49 x 10-5 for AgBrO 3 Ksp = 3.

5 EQUILIBRIUM BrO 3 TITRATION SOLUBILITY PRODUCT Ksp SEPARATION BY PRECIPITATION When (BrO 3 ) is added to a solution containing equal concentrations of Ag + and Pb 2+, which will precipitate first and why? STEP 1: reaction STEP 2: V e STEP 3: before equivalence STOICHIOMETRY! what part of analyte is left? Ksp = 5.49 x 10-5 for AgBrO 3 Ksp = 3.23 x 10-5 for Pb(BrO 3 ) 2 STEP 4: at equivalence all analyte consumed Stoichiometry! STEP 5: after equivalence excess titrant ACTIVITY EQUILIBRIUM SOLUBILITY PRODUCT K sp GAS SOLUTION WATER ACID BASE PARTITION COEFF. K H K W K a K b K 5

6 EQUILIBRIUM ACID BASE EQUILIBRIUM WATER EQUILIBRIUM K w ph BUFFERS STEP 1: reaction Weak acid With Strong base HA H + + A - NB: Equal concentrations ph = pk a (most effective buffer) STEP 2: V e # mols base added = # mols acid removed 6

7 STEP 3: before equivalence Weak acid With Strong base STEP 3: before equivalence Weak acid With Strong base BUFFER! HA H + + A - BUFFER! STEP 4: at equivalence HA H + + A - NB: at v = v e /2 concentrations are equal ph = pk a! A - + H 2 O HA + OH - K b 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? STEP 3: before equivalence Weak acid With Strong base Electrochemistry BUFFER! HA H + + A - Reduction STEP 4: at equivalence A - + H 2 O HA + OH - STEP 5: after equivalence excess OH - K b Oxidation 7

Electrochemistry How much? Faraday s constant. Electrochemistry F = (6.022 x 10 23 mol -1 ) x (1.

8 Electrochemistry How much? Faraday s constant. Electrochemistry F = (6.022 x mol -1 ) x ( x C) = 96,484 C mol -1 Current = Charge/time - I = Q/t [Ampere]=[Coulomb]/[sec] NERNST EQUATION NERNST EQUATION NB: multiplying the Reaction does NOT Change E At 25 o C 8

9 NERNST EQUATION E= E o when activities equal 1 E = 0 at equilibrium 0.50 M AgNO3(aq) M Cd(NO3)2(aq) Reference electrodes Ion selective electrode Electrolysis 9

10 Spectrophotometry Transmittance Spectrophotometry ε depends on molecule wavelength Absorbance Beer s Law Spectrophotometry Spectrophotometry λν = c [3 x 10 8 m/s] E = h ν 10

11 Spectrophotometry Spectrophotometry The fraction of atoms in the excited state is still less than 0.02%, but that fraction has increased by 100( )/1.67 = 4% Spectrophotometry Linewidth Mass spectrometry What is mass 28? N 2 CO C 2 H 4 (ethylene) H 6 B 2 (diborane) 11

12 Instrumentation 3 step program: 1. Ionize 2. Mass select 3. detect Instrumentation FT-ICR 2. Mass selection: Magnetic sector Quadrupole Time-of-flight (TOF) Ion trap Fourier transform ion cyclotron resonance Ion Mobility NB: REQUIRE VACUUM CHAMBER STEP 1: Ion Source Mass spectrometry (1)70 ev EI (2) MALDI (3) ESI 3 ways to get more out of a mass spectrum: 1. Isotopes (quantitation) 2. Exact mass (resolution + accuracy) 3. Fragmentation (MS/MS) 12

13 Mass spectrometry 1. Isotopes 1. Isotopes What does the mass spectrum of C look like? What does the mass spectrum of C look like? What does the mass spectrum of C 60 look like? Elemental clues from isotope distributions Isotopes Mass spectrometry 1. Isotopes What does the mass spectrum of C look like? What does the mass spectrum of C 60 look like? Isotope mass spectrometry Elemental clues from isotope distributions Chemical clues from isotope distributions Kinetic isotope effect 13

Fragmentation 3. Mass Fragmentation spectrometry 3. Fragmentation 1. electron impact 2.

14 Mass spectrometry 2. Mass Accuracy Mass spectrometry 2. Mass Accuracy Where do mass differences come from? <Einstein> Mass resolution m/δm Mass spectrometry 3. Fragmentation 3. Mass Fragmentation spectrometry 3. Fragmentation 1. electron impact 2. CID collision induced dissociation 3. Electron capture 4. BIRD 5. Successive fragmentation: MS/MS/MS 14

15 Chromatography Chromatography Example: V 1 = 100 ml, K = 3 (1) Extract with 500 ml (2) Extract 5 times with 100 ml And 5 times with 500 ml? Chromatography Can you improve resolution by just using a longer column (to spread out the peaks further)? Chromatography Therefore resolution improves with square root of the column length Not necessarily! 15

Chromatography MAJOR TYPES OF CHROMATOGRAPHY: Liquid -LC, HPLC Gas GC (GC-MS) Capillary electrophoresis Gel electrophoresis

nerve agent detector using single-walled carbon nanotubes.

extremely sensitive and intrinsically selective to specific gases.

16 Chromatography MAJOR TYPES OF CHROMATOGRAPHY: Liquid -LC, HPLC Gas GC (GC-MS) Capillary electrophoresis Gel electrophoresis (DNA sequencing) Novel Micro techniques Nov 14, 2003 Nanotube sensor detects nerve agents Researchers in the US have made a nerve agent detector using single-walled carbon nanotubes. Eric Snow and colleagues at the Naval Research Laboratory (NRL) in Washington say that their device is simple to fabricate, extremely sensitive and intrinsically selective to specific gases. The sensor could be used in industrial and military applications (J Novak et al Appl. Phys. Lett ). electronic nose I ~ f (receptor ΔQ) Figure 1. Gate-biased nanowire sensor Chemical and Chemical and nucleic acid nucleic acid receptors receptors 16

for the Novice Mass Spectrometry (^>, John Greaves and John Roboz yc**' CRC Press J Taylor & Francis Group Boca Raton London New York

for the Novice Mass Spectrometry (^>, John Greaves and John Roboz yc**' CRC Press J Taylor & Francis Group Boca Raton London New York Mass Spectrometry for the Novice John Greaves and John Roboz (^>, yc**' CRC Press J Taylor & Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Croup, an informa business