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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

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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

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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 addition

calibration

(-blanks)

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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

reciprocal K

ADD REACTIONSMultiply 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

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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 AgBrO3Ksp = 3.23 x 10-5 for Pb(BrO3)2

SOLUBILITY PRODUCT Ksp

SEPARATION BY PRECIPITATION

Stoichiometry!

BrO3¯EQUILIBRIUM TITRATION

STEP 1: reaction

STEP 2: Ve

STEP 4: at equivalence

STEP 5: after equivalence

STOICHIOMETRY!

STEP 3: before equivalence what part of analyte is left?

all analyte consumed

excess titrant

ACTIVITYSOLUBILITY PRODUCT Ksp

GAS SOLUTION KH

WATER KW

ACID Ka

BASE Kb

PARTITION COEFF. K

EQUILIBRIUM

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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

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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

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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

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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

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Transmittance

Absorbance

Beer’s Law

Spectrophotometry Spectrophotometry

ε depends on• molecule• wavelength

Spectrophotometry

λν = c [3 x 108 m/s]

E = h ν

Spectrophotometry

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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

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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

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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

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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. Fragmentation 3. FragmentationMass spectrometry

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Chromatography Example: V1 = 100 mL, K = 3

(1) Extract with 500 mL

(2) Extract 5 times with 100 mL

And 5

times

with 50

0 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

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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 ΔQ)

Chemical and nucleic acid receptors

Chemical and nucleic acid receptors

Figure 1. Gate-biased nanowiresensor