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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 - PowerPoint PPT Presentation
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Mini review for final
NB: This does not cover all material!
• 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
(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
(very) Rough outline
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 *
Chemical concentrations
* mass for solutions, volume for gasses
Basic tools
Randomerror
Systematicerror
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..
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.
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
0.11/0.2 = 0.55For 5 measurements Q = 0.65So…….. KEEP!
Basic tools
Internal standard
Standard additio
n
calibratio
n
(-blanks)
EQUILIBRIUM
NB:K = f(T)K ≠ f(concentrations)
K IS DIMENSIONLESS!
• Concentrations in mol/liter (M)• pressures in atmospheres (atm)• ignore solids• ignore solvents
EQUILIBRIUM
REVERSE
REACTION
recipro
cal K
ADD REACTIONS Multiply Ks
LE CHATELIER’S PRINCIPLE
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
EQUILIBRIUM
x solubility (mols/L of Ca3(PO4) that can disolve)
Gas – solution eaquilibrium KH
Henry’s Law
CO2 dissolves in water:
CO2(g) + H2O <==> H2CO3 (aq) KH = 3.4 x 10-2
at 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?
EQUILIBRIUM
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
SOLUBILITY PRODUCT Ksp
SEPARATION BY PRECIPITATION
Stoichiome
try!
BrO3¯EQUILIBRIUM
TITRATION
STEP 1: reaction
STEP 2: Ve
STEP 4: at equivalence
STEP 5: after equivalence
STOICH
IOMETR
Y!
STEP 3: before equivalencewhat part of analyte is left?
all analyte consumed
excess titrant
ACTIVITY
SOLUBILITY PRODUCT Ksp
GAS SOLUTION KH
WATER KW
ACID Ka
BASE Kb
PARTITION COEFF. K
EQUILIBRIUM
WATER EQUILIBRIUM Kw
pH
EQUILIBRIUM
ACID – BASE EQUILIBRIUM
BUFFERS
NB:Equal concentrations pH = pKa
(most effective buffer)
Weak acidWith Strong base
HA H+ + A-
STEP 1: reaction
STEP 2: Ve
# mols base added = # mols acid removed
Weak acidWith Strong baseSTEP 3: before equivalence
BUFFER! HA H+ + A-
NB: at v = ve/2 concentrations are equal pH = pKa !
Weak acidWith Strong baseSTEP 3: before equivalence
BUFFER!STEP 4: at equivalence
A- + H2O HA + OH- Kb
HA H+ + A-
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?
Weak acidWith Strong baseSTEP 3: before equivalence
BUFFER!STEP 4: at equivalence
A- + H2O HA + OH- Kb
STEP 5: after equivalence
excess OH-
HA H+ + A-
Reduction
3+ 2+
Oxidation
3+2+
Electrochemistry
F = (6.022 x 1023 mol-1) x (1.602192 x 10-19 C) = 96,484 C mol-1
How much? – Faraday’s constant.
Current = Charge/time - I = Q/t [Ampere]=[Coulomb]/[sec]
Electrochemistry
Electrochemistry
NERNST EQUATION
At 25 oC
NB: multiplying theReaction does NOTChange E
NERNST EQUATION
NERNST EQUATION
• E = Eo when activities equal 1• E = 0 at equilibrium
0.50 M AgNO3(aq)
0.010 M Cd(NO3)2(aq)
Reference electrodes
Ion selective electrode
Electrolysis
Transmittance
Absorbance
Beer’s Law
Spectrophotometry
Spectrophotometry
ε depends on• molecule• wavelength
Spectrophotometry
λν = c [3 x 108 m/s]
E = h ν
Spectrophotometry
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%
Spectrophotometry
LinewidthSpectrophotometry
http://webbook.nist.gov/chemistry/mw-ser.html
What is mass 28?
•N2
•CO•C2H4 (ethylene)•H6B2 (diborane)
Mass spectrometry
2. Mass selection:
• Magnetic sector• Quadrupole• Time-of-flight (TOF)• Ion trap• Fourier transform ion cyclotron resonance • Ion Mobility
Instrumentation
NB: REQUIRE VACUUM CHAMBER
3 step program:
1.Ionize2.Mass select3.detect
Instrumentation – FT-ICR
STEP 1: Ion Source(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)
Mass spectrometry
1. Isotopes
What does the mass spectrum of C look like?
http://www2.sisweb.com/mstools/isotope.htm
Mass spectrometry
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
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
Chemical clues from isotope distributions
Kinetic isotope effect
Isotope mass spectrometry
1. IsotopesMass spectrometry
2. Mass Accuracy
Where do mass differences come from?<Einstein>
Mass resolution m/Δmhttp://webbook.nist.gov/chemistry/mw-ser.html
Mass spectrometry
http://webbook.nist.gov/chemistry/mw-ser.html
2. Mass AccuracyMass spectrometry
3. Fragmentation
1. electron impact2. CID – collision induced dissociation3. Electron capture4. BIRD5.
Successive fragmentation: MS/MS/MS…
Mass spectrometry
3. Fragmentation3. FragmentationMass spectrometry
Chromatography
Example: V1 = 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 resolutionby just using a longer column(to spread out the peaks further)?
Not necessarily!
Chromatography
Therefore resolution improves with square root of the column length
Chromatography
MAJOR TYPES OF CHROMATOGRAPHY:
• Liquid - LC, HPLC• Gas – GC
(GC-MS)• Capillary electrophoresis• Gel electrophoresis
(DNA sequencing)
Chromatography
Novel “Micro” techniques
• electronic nose
Nov 14, 2003Nanotube sensor detects nerve
agentsResearchers 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. 2003 Appl.
Phys. Lett. 83 4026).
I ~ f (receptor Q)
Chemical and nucleic acid receptors
Chemical and nucleic acid receptors
Figure 1. Gate-biased nanowire sensor
