Summary Table for Titrimetric Analysis
Terms
Principle
Principal Requirements
Classification
Neutralisation
Oxidation/Reduction
Complex Formation
Precipitation
Methods
Colour
Voltage or current
Potentiometric
Conductimetric
Thermometric
Titration
Titrant
Titrand (analyte)
End Point
Equivalence
Point(Theoretical End
Point/Stoichiometric End
Point/Neutralization Pointii)
Titration Error
Standard Solution
Primary Standard Solution
Primary Standard(Material)
Description
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.
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 analytei until the
analyte is used up
Observe indicator colour change
Change in potential between indicator electrode and reference electrode;
pH meter
Change in electrical conductivity of the solution; use a conductivity meter
Change in temperature; measure with a thermometer
The process of adding increments of reagent solution (the titrant) to
analyte(the titrand) until their reaction is just complete.
The reagent of known concentration.(This is usually placed in the
burette.)
This is the substance being titrated; this is the substance whose
concentration is to be found.
A sudden change in a physical property of the solution.
The point when the quantity of the added titrant is the exact amount
necessary for stoichiometric reaction with the analyte(titrand).
The difference between the end point and the equivalence point caused
by sources of error.
A solution of accurately known concentration which will be used as the
titrant.
A solution of accurately known concentration that was prepared from a
primary standard material.
- Absolutely pure or of known purity
- Solid
- High Relative Molecular Mass
- Stable
- Soluble in solvent
Secondary Standard
Solution
Standardization
Direct Titration
Back Titration
Blank Titration
Indicator
Self-Indicating
Selection of acid/base
indicators
Indicator Range
Titration Curves
Uses of Titrimetric Analysis
Quality Control
- Of known RMM
- Ionic
The concentration of dissolved solute was determined by comparison
with a primary standard solution.
If the titrant cannot be prepared from a primary standard materialdetermine the concentration of the titrant by titration with a primary
standard solution.
Titrant is added to analyte(titrand) until reaction is complete.
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.
An estimation of titration error-titration done without the analyte.
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.
Does not require an auxiliary indicator. The standard solution undergoes a
detectable change in the physical properties.
- 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.
Select an indicator which exhibits a distinct colour change at a pH close to
the equivalence point
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
Principle
Application
Disadvantage
Description
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.
1. Analysis of standards: - which are to be used for the testing and/or calibration
of instrumental techniques.
2. Analyses requiring high accuracy, although the time-consuming nature of
gravimetry limits this application to a small number of determinations.
Time-Consuming
1. Accurate and precise when using modern analytical balances
2. 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
3. It is an absolute method – involving direct measurement
Methods
Precipitation
Method
Requirements
Precautions
4. Relatively inexpensive apparatus:- most expensive requirements are analytical
balance , the muffle furnace and in some cases platinum crucible
Precipitation, Volatization or evolution, electro-analytical, extraction and
chromatographic
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.
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.
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
Breakdown of topics will be provided weekly
1. Locating industrial plants; benefits and risks
- Discuss- factors which influence location of an industrial plant
- Discuss- general safety requirements for industry
2. Aluminium
- 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
3. Crude Oil
- Explain- fractional distillation of the components of crude oil
- Discuss- the uses of components [fuels/petrochemical
industry]
- Discuss – catalytic cracking & reforming
- Assess- environmental impact
4. Ammonia
5. Ethanol
6. Chlorine
7. Sulphuric Acid
8. Water
9. The atmosphere
10. Solid Waste
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
Submission
Date
2009-02-04
2009-02-04
2009-02-04
2009-02-11
2009-02-11
2009-02-18
2009-02-24
2009-03-04
2009-03-11
2009-03-18
Date
Received
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
Cosmic
Gamma
Wavelength,
Frequency, Hz, s-1 Energy,
λ, nanometres
kJmol-1
Very short
High frequency
10-3
1020
X-Rays
10-1
1018
UV
190-400
1016
12,000
Sun lamps
Visible
Infrared
400-800
103 - 105
1014
1012
310
150
Light bubs
Heat lamps
1010
0.12
106
0.0012
Microwave
ovens, police
radar, Satellite
stations
Am/FM radios
Radiation
Microwaves 1010
Radio
Waves
1011
Practical
Application
Chemical
Interactions
Radioactive
elements
X-ray Machine
Nuclear
transitions
Inner electron
transitions
Quantitative
analysis –
Redistribution
of outer
electrons in
molecular
orbitals
“
Qualitative
analysisVibration of
chemical
bonds
Molecular
rotations
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):
X-rays
10-1 100 101
Infrared
102
103 104 105
Radiowaves
1012
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
*6.02*1023
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
UV/Visible
region
Origin of
UV/Vis
spectrum
Description or Diagrams
190 nm to 800 nm [visible = 400 to 800, uv=190 to 400]
-
Colorimetry- the variation of the colour of a system with change of some
component. This is due to the formation of a 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.
-
Only some
species
absorb in
UV/Vis
region
Steps in
Analysis
Coloured
compound
s
Complexin
g agent
UV/Vis
Spectrome
ter/Spectr
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.
Radiation is absorbed by atoms and molecules when the energy of the photons exactly
matches the energy difference between the lower energy state (ground state) and one of
the higher energy state of the atoms or molecules. The wavelengths at which 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.
For example the procedure to analyse phosphate in water
Aqueous phosphates are generally colourless – converted to a coloured compound
Vandate molybdate reagent + aqueous phosphates  yellow phosphovanadaomolybdate
complex
Spectrometer- An optical instrument that possesses an optical system whih can produce
dispersion of incident electromagnetic radiation, and with which measurements can be
made of the quantity of transmitted radiation at selected wavelengths of the spectral
ophotome
ter
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.
Sensitivity
Detection
Limit
Level of sophistication varies- some instruments are simple and manual. Some are and
some are complex and automatic
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.
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
www.chemguide.co.uk/analysis/ir
www.wikipedia.org/wiki/infrared_spectroscopy
http://www.usm.edu/phillipsgroup/CHE255/IR.pdf
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
2.5 - 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
M1
M2
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
O
Asymmetrical Stretch
O
S
O
Changes dipole-peaks about 1350cm-1
Symmetrical Stretch
O
Changes dipole- peaks at about 1200cm-1
S
O
Bending
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
Sample inlet with heater
Vapour inlet
Ionisation chambers(electron gun/electron
beam/filament/ high energy electrons)
Electric Field
Process
Vaporisation
Aspiration
Ionization:- M(g) + e- M+ + 2e- Produce molecular ions/fragment ions
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
Ions are focused into a narrow kinetic energy
electrostatic analyzer)
range(double focusing)
Magnetic Field
Ions move in circular path
a) Strength of field varied
a) Ions of different M/E(mass over
b) Low magnetic field strength
electron) ration are deflected into the
c) Higher magnetic field strength
detector
b) Lightest ions are deflected readily
c) 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.