Summary Table for Titrimetric Analysis



Summary Table for Titrimetric Analysis

|Terms |Description |

|Principle |Titrimetric analysis refers to the quantitative chemical analysis carried out by determining the |

| |volume of a solution of accurately known concentration which is required to react quantitatively with|

| |a measured volume of a solution of the substance to be determined. |

|Principal Requirements |The principal requirements for a titration reaction are that it has a large equilibrium constant and |

| |proceeds rapidly. That is, each increment of titrant should be completely and quickly consumed by |

| |analyte[i] until the analyte is used up |

|Classification | |

|Neutralisation | |

|Oxidation/Reduction | |

|Complex Formation | |

|Precipitation | |

|Methods | |

|Colour |Observe indicator colour change |

|Voltage or current | |

|Potentiometric |Change in potential between indicator electrode and reference electrode; pH meter |

| |Change in electrical conductivity of the solution; use a conductivity meter |

|Conductimetric |Change in temperature; measure with a thermometer |

|Thermometric | |

|Titration |The process of adding increments of reagent solution (the titrant) to analyte(the titrand) until |

| |their reaction is just complete. |

|Titrant |The reagent of known concentration.(This is usually placed in the burette.) |

|Titrand (analyte) |This is the substance being titrated; this is the substance whose concentration is to be found. |

|End Point |A sudden change in a physical property of the solution. |

|Equivalence Point(Theoretical End |The point when the quantity of the added titrant is the exact amount necessary for stoichiometric |

|Point/Stoichiometric End |reaction with the analyte(titrand). |

|Point/Neutralization Point[ii]) | |

|Titration Error |The difference between the end point and the equivalence point caused by sources of error. |

|Standard Solution |A solution of accurately known concentration which will be used as the titrant. |

|Primary Standard Solution |A solution of accurately known concentration that was prepared from a primary standard material. |

|Primary Standard(Material) |Absolutely pure or of known purity |

| |Solid |

| |High Relative Molecular Mass |

| |Stable |

| |Soluble in solvent |

| |Of known RMM |

| |Ionic |

|Secondary Standard Solution |The concentration of dissolved solute was determined by comparison with a primary standard solution. |

|Standardization |If the titrant cannot be prepared from a primary standard material-determine the concentration of the|

| |titrant by titration with a primary standard solution. |

|Direct Titration |Titrant is added to analyte(titrand) until reaction is complete. |

|Back Titration |A known excess of one standard reagent is added to the analyte then a second standard reagent is used|

| |to titrate the excess of the first reagent. Reasons: End point is clearer by this route; the reaction|

| |will only proceed if the reagent is in excess. |

|Blank Titration |An estimation of titration error-titration done without the analyte. |

|Indicator |A compound with a physical property (usually colour) that changes abruptly near the equivalence |

| |point. This is caused by disappearance of the analyte or appearance of excess titrant. |

|Self-Indicating |Does not require an auxiliary indicator. The standard solution undergoes a detectable change in the |

| |physical properties. |

|Selection of acid/base indicators |For an indicator to be effective in a titration there should be a change of approximately 2 pH units |

| |at or near the equivalence point. |

| |In a titration between a strong acid and strong base at the equivalence point the pH is 7. |

| |If a titration involves a weak acid or a weak base the salts are hydrolysed. The pH at equivalence |

| |point is either slightly acidic or slightly alkali. |

| |Most acid/base indicators change colour within an interval of approximately 2 pH units. |

| |The colour change interval varies among indicators. |

|Indicator Range |Select an indicator which exhibits a distinct colour change at a pH close to the equivalence point |

|Titration Curves | |

|Uses of Titrimetric Analysis | |

|Quality Control |The use of Analytical techniques to monitor the quality of manufactured goods eg. Pharmaceuticals, |

| |food, standard materials, ash content of lubricating oils, nickel content of steel, |

Screened Methyl Orange

= methyl orange + a pH sensitive dyestuff (Xylene cyanol)

Colour Change Interval/Indicator Range

Phenolphthalein: pH 8.3 - 10.0

Methyl Orange: 2.9 – 4.6

January 20, 2009

1) Read text page 545

2) HW Due 2009-01-26

Collect pictures or diagrams

- Suction flask

- Suction funnel

- Sintered Glass Crucible

- Sintered Glass Funnel

- Silica Crucible

- Drying Ovven

- Muffle Oven/Furnace

- Aspirator Pump

- Vacuum Pump

- Vacuum Hoze

- Desiccator

- Desiccant

State the function of each in a gravimetric procedure

Gravimetric Analysis

- Prepare worksheet( notes, guided worksheet

- Double speed on Wednesday

|Terms |Description |

|Principle |Gravimetric analysis or quantitative analysis by weight is the process of isolating and weighing an element or a |

| |definite compound of the element in as pure a form as possible. |

|Application |Analysis of standards: - which are to be used for the testing and/or calibration of instrumental techniques. |

| |Analyses requiring high accuracy, although the time-consuming nature of gravimetry limits this application to a small |

| |number of determinations. |

|Disadvantage |Time-Consuming |

| |Accurate and precise when using modern analytical balances |

| |Possible sources of error are readily checked, since filtrates can be tested for completeness of precipitation and |

| |precipitates can be examined for the presence of impurities |

| |It is an absolute method – involving direct measurement |

| |Relatively inexpensive apparatus:- most expensive requirements are analytical balance , the muffle furnace and in some |

| |cases platinum crucible |

|Methods |Precipitation, Volatization or evolution, electro-analytical, extraction and chromatographic |

|Precipitation Method |One type of gravimetric analysis involves the formation, isolation, and mass determination of a precipitate. Generally |

| |this procedure is applied to ionic compounds. First, a sample substance of unknown composition is dissolved in water |

| |and allowed to react with another substance to form a precipitate. Then the precipitate is filtered off, washed, dried,|

| |and weighed. Knowing the mass and chemical formula of the precipitate formed, we can calculate the mass of a particular|

| |chemical component (anion or cation) of the original sample. Finally, from the mass of the component and the mass of |

| |the original sample, we can determine the percent composition by mass of the component in the original compound. |

|Requirements |Precipitate |

| |1.The precipitate must be so slightly soluble that no appreciable loss occurs when it is collected by filtration |

| |2.The particles must be of such size that they do not pass through the filtering medium- large enough to be trapped by |

| |the filter and offer reduced surface area for the attachment of impurities. |

| |3.The particle size and composition is not affected by the washing process. |

| |4. The precipitate must be convertible into a pure substance of definite chemical composition – by eg. Ignition, |

| |evaporation etc. |

|Precautions |The ideal product for gravimetric analysis by precipitation should be “insoluble”, easily filtered, very pure and |

| |should possess a known composition although few substances meet all these requirements appropriate technique can help |

| |to optimize the properties of gravimetric precipitates for eg. Decrease solubility of the precipitate by cooling the |

| |mixture. |

Volatilisation

Determination of the ash content of lubricating (motor) oils

-Weigh a clean dry porcelain crucible

-Add a clean dry porcelain crucible

-ignite in a muffle oven (lined with Magnesium Oxide MgO)

-cool crucible in a desiccator

-weigh crucible

-reignite/cool/weigh to constant mass

-calculate mass of RESIDUE ASH

Precipitation

-to measure the nickel content in steel. The alloy is dissolved in 12 mole/dm^3 of HCL and neutralized in the presence of citrate ion which maintains the iron. The slightly basic solution is warmed and Dimethylglyoxime (DMG) to precipitate red DMG-nickel complex quantitatively. The product is filtered, washed with cold water, and dried at 110 degrees Celsius

January 28,2009

|TOPIC |Submission |Date Received |

|Breakdown of topics will be provided weekly |Date | |

|Locating industrial plants; benefits and risks |2009-02-04 | |

|Discuss- factors which influence location of an industrial plant | | |

|Discuss- general safety requirements for industry | | |

|Aluminium |2009-02-04 | |

|Describe – production process/ bauxite to Al from its ores | | |

|Describe- purification of bauxite ore | | |

|Explain- uses of Al in relation to physical & chemical properties | | |

|State- energy requirements | | |

|Relate energy requirements to location of plants | | |

|Assess- environmental impact | | |

|Crude Oil |2009-02-04 | |

|Explain- fractional distillation of the components of crude oil | | |

|Discuss- the uses of components [fuels/petrochemical industry] | | |

|Discuss – catalytic cracking & reforming | | |

|Assess- environmental impact | | |

|Ammonia |2009-02-11 | |

|Ethanol |2009-02-11 | |

|Chlorine |2009-02-18 | |

|Sulphuric Acid |2009-02-24 | |

|Water |2009-03-04 | |

|The atmosphere |2009-03-11 | |

|Solid Waste |2009-03-18 | |

Practical on Gravimetric Analysis on Friday

Remaining Topics for Module 2

- Spectroscopic methods of analysis

- UV/ Visible spectroscopy

- Infrared spectroscopy

- Mass spectroscopy

- Chromatographic Methods of Separation

- Phase Separation

February 2, 2009

1. Practical

- Gravimetric

- Uncertainty

Due Friday, February 13th

2. No more graded work before Mid term

Spectroscopic Methods of Analysis- Electromagnetic Radiation

Spectroscopy, Spectrometry and Spectrophotometry- This is the measurement of electromagnetic radiation absorbed, scattered or emitted by atoms, molecules or other chemical species.

The nature of Electromagnetic Radiation

Electromagnetic radiation consists of discrete packets of energy, which we call photons. The relationship between light velocity, wavelength and frequency is:

E= h ν

E= h c/λ

µ=c/ λ

H= Plank’s constant= 6.63*10-34 JS

c= 2.998*108 ms-1 (The speed of light)

µ= Frequency measured in Hz or s-1

λ= Wavelength measured in metres( nanometres, picometres or micrometres)

Types of Electromagentic Radiation

Cosmic Rays

Gamma Rays

X-rays

UV

Visible

Infrared Microwave

Radio Waves

Characteristics of Electromagnetic Radiation

| Radiation |Wavelength, λ, |Frequency, Hz, s-1 |Energy, kJmol-1 |Practical Application |Chemical Interactions|

| |nanometres | | | | |

|Cosmic |Very short |High frequency | | | |

|Gamma |10-3 |1020 | |Radioactive elements |Nuclear transitions |

|X-Rays |10-1 |1018 | |X-ray Machine |Inner electron |

| | | | | |transitions |

|UV |190-400 |1016 |12,000 |Sun lamps |Quantitative analysis|

| | | | | |–Redistribution of |

| | | | | |outer electrons in |

| | | | | |molecular orbitals |

|Visible |400-800 |1014 |310 |Light bubs |“ |

|Infrared |103 - 105 |1012 |150 |Heat lamps |Qualitative analysis-|

| | | | | |Vibration of chemical|

| | | | | |bonds |

|Microwaves |1010 |1010 |0.12 |Microwave ovens, police |Molecular rotations |

| | | | |radar, Satellite | |

| | | | |stations | |

|Radio Waves |1011 |106 |0.0012 |Am/FM radios |Nuclear spin |

February 3, 2009

Unit 1 Module 3 2004 Paper 2

Radiation is a form of energy it may be characterised by its wavelength, λ, and its frequency, ν, so that

C= λ ν( Where c is the velocity of light in a vacuum.

UV visible light falls within the wavelength range of 380-780 nm.

In the figure identify where each of the following radiation may be found (3mks):

a) Infrared Radiation

b) Radiowaves

c) X-rays

Give a reason for your answer above. (1mk)

X-rays- have the shortest wavelength of the 3.

Radiowaves- have the longest wavelengths of the 3

Infrared- only slot remaining.

Energy is Quantized

Electromagnetic radiation consists of particles or packets of energy called photons. Each photon or quantum has a discrete energy value, E. According to the quantum theory a substance emits or absorbs electromagnetic radiation(EMR) in multiples of small amounts or quanta of energy. A change in energy is ≈≈expressed by Plank’s equation:

E2- E1= E= h ν

The energy is absorbed in whole number multiples of h ν. The energy of a substance can only change from a particular value by an integral number of quanta. All types of energy exist as distinct unconnected (discrete) energy levels.

Ultraviolet radiation of λ of 120 nm. A material absorbs UV radiation.

How much E does it absorb?

C= λ ν

2.998*108 =120*10-9 * f

E= h ν

E= 6.63*10-34 * 2.5*1015

E= 1.66*10-18 J

E= 9.99714 ≈ 997.15 kJ Ans

February 4, 2009

UV/Visible Spectroscopy

1. UV/Visible region: 190-400 nm [visible=400-800, UV=190-400]

2. Origin

|Terms |Description or Diagrams |

|UV/Visible region|190 nm to 800 nm [visible = 400 to 800, uv=190 to 400] |

|Origin of UV/Vis |Colorimetry- the variation of the colour of a system with change of some component. This is due to the formation of a |

|spectrum |coloured component. This is usually due to the formation of a coloured compound by the addition of appropriate reagent, or |

| |the colour may be inherent in the desired constituent itself. |

| | |

| |Ultraviolet and visible spectroscopy are based on the energy changes that occur within molecules and ions when radiation |

| |from the ultraviolet and visible regions of the electromagnetic spectrum are absorbed. |

| | |

| |When light interacts with a substance which has an absorption in the visible region of the spectrum, a characteristic |

| |portion of the mixed wavelengths is absorbed [red orange yellow blue violet]. The remaining wavelengths are transmitted and |

| |the substance will assume the complementary colour of the wavelength(s) absorbed. When all visible light is absorbed, a |

| |substance appears black, If light between 400 nm and 800 nm is not absorbed, the substance is colourless. |

|Only some species|Radiation is absorbed by atoms and molecules when the energy of the photons exactly matches the energy difference between |

|absorb in UV/Vis |the lower energy state (ground state) and one of the higher energy state of the atoms or molecules. The wavelengths at which|

|region |organic molecules absorb radiation depends on how tightly their electrons are bound. The shared electrons in single bonds |

| |such as C-H are firmly held and do not easily absorb in the uv/vis region. The electrons in double and triple bonds are more|

| |loosely held and so more easily excited. Organic compounds ( e.g. methyl orange) containing these bonds give more |

| |absorption peaks in the ultraviolet and visible regions. Unshared outer electrons, that is lone pairs that are localized |

| |around atoms such as oxygen, nitrogen and the halogens are loosely bound and absorb in the UV/Vis regions of the spectrum. |

| |Organic compounds that absorb in the ultraviolet region only (below 400nm) are colourless. |

|Steps in Analysis|For example the procedure to analyse phosphate in water |

|Coloured |Aqueous phosphates are generally colourless – converted to a coloured compound |

|compounds | |

|Complexing agent |Vandate molybdate reagent + aqueous phosphates ( yellow phosphovanadaomolybdate complex |

|UV/Vis |Spectrometer- An optical instrument that possesses an optical system whih can produce dispersion of incident electromagnetic|

|Spectrometer/Spec|radiation, and with which measurements can be made of the quantity of transmitted radiation at selected wavelengths of the |

|trophotometer |spectral range. |

| | |

| |Photometer- A device for measuring the intensity of transmitted radiation |

| | |

| |Spectrometer + Photometer = Spectrophotometer |

| | |

| |Spectrophotometer- produces a signal corresponding to the difference between the transmitted radiation of a reference |

| |material and that of a sample at selected wavelengths. |

| | |

| |Level of sophistication varies- some instruments are simple and manual. Some are and some are complex and automatic |

|Sensitivity |Sensitivity is a complex concept. A simple way to view sensitivity: |

| |Sample A has a nitrate concentration of 0.8925µgcm-3[ Reported as: 1,0.9,0.89,0.893,.89250] |

| |Sample B has a nitrate concentration of 0.8549 µgcm-3[Reported as:2,0.9,0.85,0.850,0.855,0.85490] |

| |These small numerical differences are important when analysing medical samples. |

| | |

| |The values: A= 0.89 or B=0.85 could make the difference in a person testing positive or negative for an illness. |

|Detection Limit |The lowest concentration that can be detected. If detection limit is 10ppm, then a concentration of 5ppm will be measured as|

| |0ppm. A result of 0ppm should be reported as 10ppm. |

February 9, 2009

Infrared Spectroscopy

chemguide.co.uk/analysis/ir

wiki/infrared_spectroscopy



Ausetute

Wave number cm-1 (1/λ)

3 Main Regions

Near IR (overtone region) 0.8-2.5 µm (12,500 – 4000 cm-1)

Middle IR (vibration-rotation region) 2.5-50 µm (4000-200 cm-1)

Far IR (rotation region) 50-1000 µm (200-10 cm-1)

Main region of interest for analytical purposes

5. - 25 µm

4000 – 400 cm-1

Left Side 4000-1500 cm-1 (shorter wavelength, higher energy)-FUNCTIONAL GROUP REGION

Right Side 1500-500 cm-1 (complicated absorptions due to bending vibrations within the molecule, this is unique for a molecule)-FINGERPRINT REGION

Background to IR Spectroscopy

Infrared Spectroscopy is one type of vibrational spectroscopy.

Simple Harmonic Motion

- Two spheres or masses connected with a spring

Simple Harmonic Oscillator

Once set in motion the sphere will oscillate or vibrate back and forth on the spring ata certain frequency depending on:

- The masses of the spheres

- The stiffness of the spring

- Smaller masses will oscillate at higher frequencies than larger masses

- A very stiff spring is hard to deform and quicklt returns to its original shape when the deforming force is removed

- Weak springs are easily deformed and take more time to return to their original shape

- Stiffer springs will oscillate at a higher frequency than weaker ones

A chemical bond between two atoms can be thought of as a simple harmonic oscillator as seen above. In the case of atoms the:

- Bond= Spring

- Atoms or Groups of Atoms = The masses

Every atom has a different mass. Single, double and triple bonds have differing degrees of stiffness.

Each combination of atoms and bonds has its own characteristic harmonic frequency.

When an object is vibrating at a certain frequency then encounters another vibration of exactly the same frequency the oscillator will absorb the energy of the vibration it encounters.

At any temperature above absolute zero all the simple harmonic oscillators that make up any molecule vibrate vigorously.

IR light just happens to be in the same frequency range as a vibrating molecule.

If a vibrating molecule is bombarded with some IR light it will absorb those frequencies in the light which exactly match the frequency of the different harmonic oscillators that make up that molecule.

When the light is absorbed the little oscillators in the molecule will continue to vibrate at the same frequency but since they have absorbed the energy of the light they will have a larger amplitude of vibration. This means that the “springs”/ bonds will stretch further than before the light was absorbed. The remaining light which was not absorbed by dr if the oscillators in the molecule is transmitted through the sample to a detector. A computer will analyse the transmitted light and determine which frequencies were absorbed.

IR Clarification Notes

Molecules are able to rotate about an axis through the centr of gravity of the molecule and bonds within the molecule may vibrate in a variety of ways.

In addition to electronic transitions in a compound ( in atomic and molecular orbitals) there are other discrete “allowed”energy levels that exist.

The absorption and emission of energy iin the IR region of the spectrum may accompany or be separated from the electronic transitions which occur in the UV/Vis regions

The absorption of IR radiation arises from the quantization of vibrational energy within molecules. Only certain frequencies(energies) of IR radiation will be absorbed by a given molecule. The absorptions correspond to the stretching and bending frequencies of the bonds in covalent molecules.

For the bond within a molecule to absorb within the IR region:

• Wavelength of radiation must exactly match the wavelength of the bond vibration

• The bond must have a dipole

• The bond must contain a changing dipole

SO2(polar) : S Asymmetrical Stretch

O O Changes dipole-peaks about 1350cm-1

S Symmetrical Stretch

O O Changes dipole- peaks at about 1200cm-1

S Bending

O O

Changes Dipole- peak at about 500 cm-1 (finger print region)

CO2: O C O Asymmetrical Stretch

Dipole Changes- Peaks at about 2350 cm-1

O C O Symmetrical Stretch

Dipole does not change

No IR peak

O C O Bending( 2 degenerate modes at right angles)

Changes Dipole- peaks at about 700 cm-1(finger print region)

NB Symmetrical bonds eg. Cl2, H2,O2 and N2 DO NOT SHOW IR ABSORPTION.

February 16, 2009

Mass Spectroscopy

Text- pg. 552-553

- Principles

• Apparatus

• Process

- Interpret Spectra

|Mass Spectrometer |Process |

|Sample inlet with heater |Vaporisation |

|Vapour inlet |Aspiration |

|Ionisation chambers(electron gun/electron beam/filament/ high |Ionization:- M(g) + e- (M+ + 2e- |

|energy electrons) |Produce molecular ions/fragment ions |

|Electric Field |Acceleration (ions concentrated into a narrow beam) |

|Vacuum pump |Removes atmospheric gases from apparatus before sample is |

| |injected(1*10-7 kPa) |

|Electrostatic Analyzer(not all machines have an electrostatic |Ions are focused into a narrow kinetic energy range(double focusing)|

|analyzer) | |

|Magnetic Field |Ions move in circular path |

|Strength of field varied |Ions of different M/E(mass over electron) ration are deflected into |

|Low magnetic field strength |the detector |

|Higher magnetic field strength |Lightest ions are deflected readily |

| |Ions of increasing mass are deflected and focused on the detector |

|Detector |An electric current is produced when ions strike the detector |

|Amplifier |Detector current flows through an amplified |

|Recorder |Mass spectra/ mass spectrometer trace may be printed or displayed on|

| |a computer screen |

For ions of a given M/E value, the detector current is proportional to the relative abundance of that type of ion in the sample being analyzed. Mass spectra is usually recorded as line diagrams of relative abundance plotted against M/E ratio on which only the major peaks are shown. The abundance of each fragment ion is represented as a percentage of the most abundant (stable) fragment which is called the base peak. The base peak has a relative abundance of 100%.

The molecular ion peak is from the ion of the original molecule and the base peak is the most abundant ion.

-----------------------

[i] A solution of unknown concentration

[ii] Only in the case of acid/base titration.

-----------------------

X-rays

Infrared

Radiowaves

10-1 100 101 102 103 104 105 1012

*6.02*1023

M2

M1

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