Summary Table for Titrimetric Analysis
Terms / DescriptionPrinciple / 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
Voltage or current
Potentiometric
Conductimetric
Thermometric / 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
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 Point/Stoichiometric End Point/Neutralization Point[ii]) / The point when the quantity of the added titrant is the exact amount necessary for stoichiometric reaction with the analyte(titrand).
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 worksheetà notes, guided worksheet
- Double speed on Wednesday
Terms / DescriptionPrinciple / 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 / 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.
Disadvantage / 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
4. 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
TOPICBreakdown of topics will be provided weekly / Submission
Date / Date Received
1. Locating industrial plants; benefits and risks
- Discuss- factors which influence location of an industrial plant
- Discuss- general safety requirements for industry / 2009-02-04
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 / 2009-02-04
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 / 2009-02-04
4. Ammonia / 2009-02-11
5. Ethanol / 2009-02-11
6. Chlorine / 2009-02-18
7. Sulphuric Acid / 2009-02-24
8. Water / 2009-03-04
9. The atmosphere / 2009-03-11
10. 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, nanometres / Frequency, Hz, s-1 / Energy, kJmol-1 / Practical Application / Chemical InteractionsCosmic / 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 radar, Satellite stations / Molecular rotations
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 νè 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 DiagramsUV/Visible region / 190 nm to 800 nm [visible = 400 to 800, uv=190 to 400]
Origin of UV/Vis spectrum / - 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.
- 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 absorb in UV/Vis region / 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.
Steps in Analysis / For example the procedure to analyse phosphate in water
Coloured compounds / Aqueous phosphates are generally colourless – converted to a coloured compound
Complexing agent / Vandate molybdate reagent + aqueous phosphates è yellow phosphovanadaomolybdate complex
UV/Vis Spectrometer/Spectrophotometer / 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 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