Chem 222ramsey1.chem.uic.edu/chem222/Lecture/Lecture13_050221.pdf · 2005. 2. 22. · Step1 )...
Transcript of Chem 222ramsey1.chem.uic.edu/chem222/Lecture/Lecture13_050221.pdf · 2005. 2. 22. · Step1 )...
Chem 222
#12 Ch18Feb 22, 2005
Announcement
• Advice: KH 3-14 Exp (Nicotine in Tobacco) smells quite nasty. So wear lab coat.
• KH 3-14 Exp Handout Website Report Cover
Sheets and HandoutsHANDOUT KH 3-14
• Don’t be late for the class!
Q3
• 2b When you decrease pH, how does the concentration of free Ca2+ change? Does it increase or decrease? Explain the reason.
• Kf’ = αY4Kf = [CaY2-]/[Ca2+][EDTA]
Nicotine
H—+
H—+
H+
B BH+ BH2+
(Read P234)
KH 3-14
Nicotine1 mol
H+ (in Acetic Acid Solvent)2 moles
From HClO4
Warning:•Glacial Acetic Acid Very Corrosive• Perchloric Acid Strong Oxidant
(May Explode with Organic Solvent)
Wear Nitrie Gloves and Goggles
(b) Titration of 10.0 mL of 0.100 M nicotine(pKb1 =6.15, pKb2 =10.85) with 0.100 M HCl
P232 (Ch 12)
The second H+ does not completely react with Nicotine in H2O
Ch. 18 Fundamental Spectrophotometry
How ozone is formed
How ozone is decomposed by Freon-12 (CCl2F2)
Ozone layer absorb UV light
Applications of Spectrophotometry
♦ Measurement of concentration♦ Detector of molecules in HPLC
(19-4)♦ Cell imaging with probe dyes♦ Immunoassays (19-5)♦ Conformation analysis by IR
18-1 Properties of Light
• The wave length λ is the crest-crest distance between waves
The frequency ν is the number of complete oscillations that the wave makes each second
Relation between λ and νλ ×ν = c (18-1)
Light has characters as both of a wave and a particle
A light particle called photon has energy of
E =hν, (18-2)where h is Plunck’s constant 6.626 ×10-34 J-s
Wave length, Energy, Frequency, Wave Number
Higher Energy Lower Energy
E = hν = hc/λ = hc ν (18-3)↑
ν = c/λ
~
Wave Number: ν = 1/ λFor wave number, a unit of cm-1 is still commonly used
~
(Memorize this)
Example (p409)
A single photon has energy of
∆E = hc/[Q1] =(6.626×10-34 J/s)(2.998×108
m/s)/(147×10[Q2]m)= 1.35 × 10-18 [Q3 unit? ]
For 1 moles of molecules,
∆Emoles = (1.35 × 10-18) ×(6.022 × 1023)
= 814
• When light is absorbed by a sample, the irradiance of the beam of light is decreased.
• Irradiance P: the energy per second per unit area of the light beam--• --• --•--• --• --• P = Nhν
--• --• --• ☺ ☺ --• --•--• --• --• ☺ --•
P0 P
Molecules Absorb Photons
Transmittance: T = P/P0
hv
Sample Cells or Cuvets
Absorbance & Transmittance
• T = P/P0 ( 0 ≤ T ≤ 1)Percentage transmittance %T = 100 T
Absorbance is defined• A = -log(P/P0) = -log(T)
Q. How much is A for the following P(a) P = 0.001P0(b) P = 0.1P0
Beer’s LawA = εbCC: Concentration b: Path length (Thickness of your sample)[cm]ε: Molar Absorptivity [M-1cm-1]
Answer See Box 18-1
↑Different depending on molecules and λ
Usable to characterize molecules
Absorption spectra of Chlorophyll a & b
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/ActionSpectrum.html
Examples (p412)• Find the absorbance and transmittance of
a 0.00200 M solution of a substance with a molar absorptivity of 250 M-1cm-1 in a cell with 2.00 cm path length.
A = (250 M-1cm-1) [Q1] [Q2] = 1.00
A = -logT T = 10 –A
A = 10 [Q3] = [Q4]
Note:Beer’s law usually work for a dilute solution (≤ 0.01 M) When c is high, molecules start to interact.
Ex. Monomer to Dimmer ε changes
Absorption Spectrumwave length dependence of ε
• A = εbc
Visible absorption spectrum of (ferrozine)3Fe(II)
λ (nm)
ε(M
-1cm
-1)
Sweep λ and measure A
Serum Iron Determination (p416)
• Serum normally contains 1 µg of Fe in 1 mL of serum in a form of complex with transferrin(protein).
Step1 ) Reduce Fe3+ (use thiglycolic acid or vitamin C)
Step 2 ) Add trichloroacetic acids to remove proteins
Step 3) Transfer supernutant, and add ferrozine
Human Blood: 45 % cells, 55 % plasmaIf you remove anticoagulutant (blood clot) Serum
Calibration curve for A = kC
↑
562 nm
Try example in p418