IB 化学 选修 1 Option 1 Modern Analytical Chemistry 讲义

Chemistry Higher Level

Option 1: Modern Analytical Chemistry

Quick Review Guide

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Mr. Pan Guanwen

7th Edition

Content

A1 Analytical Techniques ..................................................................................................................................... 4

A1.1 State the reasons for using analytical techniques. ........................................................................................ 4 A1.2 State that the structure of a compound can be determined by using information from a variety of analytical techniques singularly or in combination. ............................................................................................. 4

A2 Principles of Spectroscopy ..............................................................................................................4

A2.1 Describe the electromagnetic spectrum ....................................................................................................... 4

A2.2 Distinguish between absorption and emission spectra and how each is produced ...................................... 4

A3 Infrared Spectroscopy .................................................................................................................................... 5

A3.1 Describe the operating principles of a double beam spectrometer .............................................................. 5 A3.2 Describe how information from an IR spectrum can be used to identify bonds .......................................... 5 A3.3 Explain what occurs at a molecular level during the absorption of IR radiation by molecules. .................. 5 A3.4 Analyze IR spectra of organic compounds (up to three functional groups) ................................................. 6

A4 Mass spectrometry .......................................................................................................................................... 6

A4.1 Determine the molecular mass of a compound from the molecular ion peak .............................................. 6

A5 Nuclear Magnetic Resonance (NMR) spectroscopy .............................................................................. 7

A5.1 Deduce the structure of a compound given information from it 1H NMR spectrum .................................. 7 A5.2 Outline how NMR is used in body scanners (an important application of NMR spectroscopy) ................. 7

A9 NMR spectroscopy [HL]................................................................................................................................ 8

A9.1 Explain the use of tetramethylsilane (TMS) as the reference standard ........................................................ 8 A9.2 Analyse 1H NMR spectra. ........................................................................................................................... 8

A6 Atomic Absorption (AA) Spectroscopy ..................................................................................................... 8

A 6.1 State the use of Atomic Absorption spectroscopy ....................................................................................... 8 A 6.2 Describe the principles of atomic absorption .............................................................................................. 9 A6.3 Describe the use of each of the following components of the Atomic Absorption spectrometer: fuel, atomizer, monochromatic light source, monochromatic detector, read-out. ......................................................... 9 A6.4 Determine the concentration of a solution from a calibration curve. ......................................................... 10

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A7 Chromatography ........................................................................................................................................... 10

A7.1 State the reasons for using chromatography .............................................................................................. 10 A7.2 Explain that all chromatographic techniques involve adsorption on a stationary phase and partition between a stationary and a mobile phase. ........................................................................................................... 10 A7.3 Outline the use of paper chromatography, thin-layer chromatography (TLC) and column chromatography: ............................................................................................................................................................................. 11 A10.1 Describe the techniques of gas-liquid chromatography (GLC) and high-performance liquid chromatography (HPLC) ..................................................................................................................................... 11 A10.2 Deduce which chromatographic technique is most appropriate for separating the components in a particular mixture. .............................................................................................................................................. 14

A8 Visible and Ultraviolet (UV-VIS) .............................................................................................................. 14

A8.1 Describe the effect of different ligands on the splitting of the d orbitals in transition metal complexes ... 14 A8.2 Describe the factors that affect the colour of transition metal complexes ................................................. 15 A8.3 State that organic molecules containing a double bond absorb radiation .................................................. 15 A8.4 Describe the effect of the conjugation of double bonds in organic molecules on the wavelength of the absorbed light. .................................................................................................................................................... 15 A8.5 Predict whether or not a particular molecule will absorb ultraviolet or visible radiation. ......................... 16 A8.6 Determine the concentration of a solution from a calibration curve using the Beer-Lambert Law. .......... 16

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A1 Analytical Techniques

A1.1 State the reasons for using analytical techniques.

Analytical techniques can determine 1. a sample’s structure,

2. composition of substances, 3. purity,

4. concentration of substance and identify substance. They are faster, more precise and easier to use.

A1.2 State that the structure of a compound can be determined by using information from a variety of analytical techniques singularly or in combination.

A2 Principles of Spectroscopy

A2.1 Describe the electromagnetic spectrum

It holds all electromagnetic radiation with every frequency.

A2.2 Distinguish between absorption and emission spectra and how each is produced

Emission spectra:

1. Radiation emitted by electron from higher/excited state to lower/ground energy level. 2. Regions/lines corresponding to energies given out/emitted

Absorption spectra:

1. Energy required to move/excite (electrons) from lower/ground state to higher energy level/excited state.

2. Continuous spectrum with missing regions/lines corresponding to energies absorbed.

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A3 Infrared Spectroscopy

A3.1 Describe the operating principles of a double beam spectrometer

Sample beam

Diagram must be shown! reference beam

1. Monochromator creates single wavelength.

2. The beam is split to two identical rays by rotating mirror and then, passes through sample and reference respectively.

3. Compare the sample and reference 4. Photomultiplier detects the signal

A3.2 Describe how information from an IR spectrum can be used to identify bonds

Use peak’s wave number to find out the type of chemical bonds with the table on IB booklet.

A3.3 Explain what occurs at a molecular level during the absorption of IR radiation by molecules.

1. Changes bond angle (bending)

2. Changes bond length changes (stretching)

 Symmetrical stretching and asymmetrical stretching H-H symmetrical stretching; H-N asymmetrical stretching

3. Changes polarity

4. Changes the dipole moment

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A3.4 Analyze IR spectra of organic compounds (up to three functional groups)

Use peak’s wave number to find out the type of chemical bonds with the table on IB booklet.

A4 Mass spectrometry

A4.1 Determine the molecular mass of a compound from the molecular ion peak

Convert the sample to atom or molecule in gaseous phase Gaseous molecules (bombard by e-) cations (+) Cations were accelerated through an electric field Deflected by a magnetic field

The cation with certain mass could reach the final detector and then, send the signal of the collision location and number to computer.

   

(vaporization) (ionization) (acceleration) (deflection) (detection)

Smaller the mass, the greater the deflection By varying the strength of the magnetic fielde5

Ions of differing mass can brought to focus on the detector. Greater the magnetic strength, greater the mass

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Read the peak of mass to charge ratio in the spectrum to find out the molecular mass.

A4.2 Analyze fragmentation patterns in a mass spectrum to find the structure of a compound

Remember! All m/z value shows the mass of CATION (+), NOT THE MOLECULES! Shift 14 15 17 29 45 77

Name of particles (CH2) (CH3) (OH) (C2H5 ) or (H-CO) (COOH) (C6H5) + + ++ + ++A5 Nuclear Magnetic Resonance (NMR) spectroscopy

A5.1 Deduce the structure of a compound given information from it 1H NMR spectrum

Chemical shift:

Number of different chemical shift: The area under the curve: Splitting pattern:

the type of hydrogen environment

the number of different types of hydrogen environment the number of hydrogen atoms in each environment.

number of hydrogen/protons attached to neighboring carbon.

Identify the region of the electromagnetic spectrum used in NMR spectroscopy. It uses radio wave.

A5.2 Outline how NMR is used in body scanners (an important application of NMR spectroscopy)

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1. Magnetic resonance imaging (MRI) gives a three-dimensional view of organs in the human body. 2. Because protons in water molecules/lipids/carbohydrates in human cells give different signals, depending upon their environment

3. Different water-lipid ratios/hydrogen atoms in different chemical environments absorb different

(radio) frequencies;

A9 NMR spectroscopy [HL]

A9.1 Explain the use of tetramethylsilane (TMS) as the reference standard

1. 2. 3. 4. 5.

Tetramethylsilane (TMS) (CH3)4Si is chemically inert,

producing a single strong signal (12 H atoms shares identical chemical environment

it absorbs radiation of a frequency rather different from that of most other organic compounds it doesn’t interfere with their absorption signals.

The chemical shift is then measured relative to this arbitrary standard being taken as zero

A9.2 Analyse 1H NMR spectra.

Splitting pattern

Determine the number of hydrogen atom on neighboring carbon atoms

In general, an NMR will be split into N+1 peaks where N= number of hydrogen atoms on the adjacent atom or atoms.

The carbonyl group does shield the hydrogen atoms on the adjacent atom or atoms. For example:

If there are no hydrogen on the adjacent atoms, then the resonance will remain a single peak. If there are 3 hydrogen atoms on the adjacent atoms, the resonance will be split into four peaks.

Example A:

Peak 2 3 4 Splitting Pattern Triplet Sextet Triplet Proton C B A A6 Atomic Absorption (AA) Spectroscopy

A 6.1 State the use of Atomic Absorption spectroscopy

AA is a technique to determine the type of metal ion (qualitative) and its concentration

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(quantitative)

A 6.2 Describe the principles of atomic absorption

The non-excited vaporized metal atom absorbs its characteristic frequency from an external source and becomes excited.

A6.3 Describe the use of each of the following components of the Atomic Absorption spectrometer: fuel, atomizer, monochromatic light

source, monochromatic detector, read-out.

Step one: Sample is dehydrated (solvent, water is evaporated); ion samples are converted to atoms at ground state. (Fuel and atomizer)

Step two: the monochromatic light source is used to select a wavelength to be passed to the detector.

Step three: the intensity of the transmitted light is compared to the intensity of the incident light, and the absorbance is calculated.

1. The fuel:

to form a combustion mixture/to produce heat

2. The atomizer

turns all the ions in the sample into atoms

3. The monochromatic light source

provides light that is absorbed by the lead/metal to be detected/provides light from excited atoms of lead/metal being detected.

4. The monochromatic light detector

The detector reads only the light from excited atoms of metal being detected and, then compares with the initial light intensity.

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A6.4 Determine the concentration of a solution from a calibration

curve.

Step One: make up different solutions of known concentrations Step Two: measure the absorbance for each concentration

Step Three: plot a calibration/absorbance against concentration curve

Step Four: read the value of unknown concentration from its absorbance/compare the absorption of the unknown with the standard solutions

A7 Chromatography

A7.1 State the reasons for using chromatography

It is used to separate mixtures of substances into their pure components.

Some chromatography techniques are able to determine the component structures by their retention time.

A7.2 Explain that all chromatographic techniques involve adsorption on a stationary phase and partition between a stationary and a mobile phase.

Adsorption Partition

Stationary phase

Solid Liquid

Mobile phase

Liquid Liquid/gas

Stationary phase: phase that doesn’t move

phase that moves through the stationary phase. Mobile phase:

distribution between the stationary phase and mobile phase. Partition:

Components in a mixture have different tendencies to dissolve in a solvent. it involves the way a substance bonds to the surface of a solid stationary phase. Adsorption:

Components in a mixture have different tendencies to adsorb onto a surface. the distance travelled by one component divided by the distance travelled by the Rf value:

solvent.

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A7.3 Outline the use of paper chromatography, thin-layer chromatography (TLC) and column chromatography

A10.1 Describe the techniques of gas-liquid chromatography (GLC) and high-performance liquid chromatography (HPLC)

Technique Paper chromatography Thin layer chromatography Column chromatography Gas-liquid chromatography High Performance Liquid Chromatography Stationary Phase Trapped water in the paper Oxide coating Silica oxide or non-volatile liquid Alkane/long chain hydrocarbon Silica and long chain hydrocarbon Mobile Phase Organic solvent Organic Solvent Organic solvent N2(g)/He(g)/Ar(g) Hexane/water/alchohol/solvent/Liquid Technique Paper chromatography Thin layer chromatography (TLC) Similarity To tell the number of different substances are there inside this mixture Could have the same stationary phase as TLC Difference Poorer separation; run slower Stationary phase Better separation; run faster Stationary phase It could not only tell the number of different substances, but also separate them. Column chromatography

1. Paper Chromatography:

It is the simplest kind of chromatography, just for a simple test.

Procedures:

1. place sample on paper 2. elute suitable solvent

3. wait till solvent reaches solvent front 4. measure Rf value

5. Compare with known value to find out the kind of substance.

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2. Thin-Layer Chromatography (TLC)

The difference between paper chromatography is that the stationary phase is different (oxide coating, silica). But, TLC is much more precise than paper one.

3. Column Chromatography

Procedures:

1. Tube with silica.

2. Saturated with solvent. 3. add sample at top 4. tap opened at bottom

5. more solvent added substances collected in separated

containers.

Rf value:

Rf value can identify components in the sample in paper and thin-layer chromatography

Distance moved by componentRf=

Distance moved by solvent

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3. Gas-liquid chromatography (GLC)

Valid for: identify compounds that can vaporize without decomposing

urine samples from athletes for drugs 1. 2. underground mine gases 3. blood alcohol levels Procedures: 1．sample is vaporized/heated; 2．mobile phase is inert gas;

3．stationary phase is a liquid/long chain alkane/grease on a solid support;

4．less volatile components have longer retention time; 5．measure retention time for reference and sample 6． components detected by flame ionizer;

7． converted to electrical current / connected to chart recorder;

8．if reference and sample have the same retention time, then, they are the same substance.

or

measure peak sizes for pure reference and mixture of reference and sample;

if reference present in sample then peak size greater for mixture (under same conditions);

X-axis: retention time, the time when such component comes out of the column y-axis: peak height, the abundance of this compound

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1. High Performance Liquid Chromatography (HPLC)

Valid for: non-volatile and ionic substance 1. Analyzing oil, alcoholic beverages, antioxidants, sugars and vitamins in food, 2. Pharmaceuticals, polymers, 3. Biochemical and biotechnology research; 4. Quality control of insecticides and herbicides.

A10.2 Deduce which chromatographic technique is most appropriate for separating the components in a particular mixture.

Name of chromatographic technique GLC HPLC Column Chromatography Paper chromatography and TLC

Specific part See above! Preparative purpose (separate some components) Simple qualitative check A8 Visible and Ultraviolet (UV-VIS)

It could determine the metal ions complex and extension of double bonds of organic compound.

A8.1 Describe the effect of different ligands on the splitting of the d orbitals in transition metal complexes

The color of metal complexes depends on the ligand’s electron density. 1. What is the electron density?

a) Greater the bonding pair electrons percentage among all pair electrons, greater the electron density.

i. Electron density

1. NH3> H2O> Cl-

a) H2O has 2 bonding pairs and 2 lone pairs electrons. b) NH3 has 3 bonding pairs and 1 lone pair electrons. c) Cl- has 3 lone pairs and no lone pair electron

d) Therefore, Cl- has less electron density and the NH3 has the greatest electron density

Greater the electron density of ligand, greater the split of d-orbital, absorb higher frequency of energy to excite electrons from lower splitted d-orbital to higher one.

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Example: Electron density of ligand Gap between d-orbital Color [Cu(H2O)6]2+ Low Less Sky blue [Cu(NH3)4(H2O)2]2+ high Greater Royal blue Because the energy gap between d-orbitals increases.

A8.2 Describe the factors that affect the colour of transition metal complexes

1. The element being considered (especially the nuclear charge):

different nuclear charge causes the d orbitals to split differently 2. The charge on the ion

different oxidation number affects the size of the d orbital splitting. 3. The electron density of ligands surrounding the ion

the more electron-dense the ligand the greater the splitting of the d orbitals. 4. the number and geometrical arrangement of the ligands

A8.3 State that organic molecules containing a double bond absorb radiation

A8.4 Describe the effect of the conjugation of double bonds in organic molecules on the wavelength of the absorbed light.

More extensive conjugation of double bonds/more alternate single and double bonds/involving more delocalization of pi elections;

Less energy is required (to excite the electrons); Absorption occurs in the visible region.

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Question:

In terms of the color of phenolphthalein in acid and basic solution, which one is more conjugated?

A8.5 Predict whether or not a particular molecule will absorb ultraviolet or visible radiation.

UV Visible light Less extensive conjugation of double bonds/less More extensive conjugation of double bonds/ less alternate double bond alternate double bond More energy is required Less energy is required A8.6 Determine the concentration of a solution from a calibration

curve using the Beer-Lambert Law.

1. Greater the concentration 2. Greater the absorption

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