a quantitative analytical method which involves measurement of the volume of a solution whose concentration is known and applied to determine the concentration of the analyte.
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Jean-Baptiste-Andre-Dumas
The first method of Volumetric Analysis was devised and found by the French chemist
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1. Solution to analyzed is an unknown amount of chemicals 2. The reagent of unknown concentration reacts with a chemical of an unknown amount in the presence of an indicator (mostly phenolphthalein). 3. The volumes are measured by titration which completes the reaction between the solution and reagent. 4. The volume and concentration of reagent which are used in the titration show the amount of reagent and solution. 5. The amount of unknown chemical in the specific volume of solution is determined by the mole fraction of the equation.
Basic principles of volumetric analysis
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Titration
A quick, accurate and widely-used way of measuring the amount of a substance in a solution.
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Titrants
Standard solution with known concentration needed to react with an unknown quantity of a second substance.
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Stoichiometric reaction
Reaction with definite whole number ratio between a and b
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Endpoint
An abrupt change in some physical and chemical property of the sample solution
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Endpoint
The point at which some detection technique tells you that chemical equivalence has been reached.
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Equivalence point
The point at which just sufficient reagent is added for complete reaction with the sample. It is the point of stoichiometric chemical equivalence.
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Indicator
It shows the endpoint of the titration, usually by change of color, and the endpoint and equivalence point should coincide.
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Standard solution
It is a solution of known concentration.
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Standardization
It is a process of determining the concentration of an unknown solution.
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Primary Standard
It is a substance used for standardization.
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equivalence point
a theoretical point reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample.
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titration error
The difference in volume or mass between the equivalence point and the end point
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Indicators
often added to the analyte solution to produce an observable physical change (the end point) at or near the equivalence point.
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• Colorimeters • Turbidimeters • Temperature monitors • Refractometers • Voltmeters • Current meters • Conductivity meters
Instruments Used in Measuring End Points
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primary standard
a highly purified compound that serves as a reference material in volumetric and mass titrimetric methods
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1. High purity 2. Atmospheric 3. Absence of hydrate water 4. Modest cost 5. Reasonable solubility in the titration medium 6. Reasonably large molar mass
Important requirements for a primary standard are the following:
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By standardization, in which the titrant to be standardized is used to titrate
play a central role in all titrimetric methods of analysis
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a. a weighed quantity of a primary standard, b. a weighed quantity of a secondary standard, or c. a measured volume of another standard solution.
By standardization, in which the titrant to be standardized is used to titrate
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NEUTRALIZATION
- An acidic substance is titrated with a standard solution of an alkali (acidimetry) or a basic substance with a standard solution of acid (alkalimetry).
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OXIDATION-REDUCTION (REDOX)
reducing substance is titrated with a standard solution of an oxidizing substance is titrated with a standard solution of a reducing agent.
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PRECIPITATION/SATURATION
A substance is titrated by precipitating it with a standard solution of precipitating agent.
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COMPLEX FORMATION
A substance is titrated with a standard reagent to a formation of a complex
PROCESSES IN VOLUMETRIC ANALYSIS (By Reaction Type)
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1. Spectrophotometric 2. Electrochemica 3. pH
PROCESSES IN VOLUMETRIC ANALYSIS (By Indicator)
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Spectrophotometric
A method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelength
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Electrochemica
Is used to sense the presence or change in concentration of the oxidized and reduced forms of a redox couple
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pH
- are weak acids that exist as natural dyes and indicate the concentration of H+ (H3O+) ions in a solution via color change.
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1. Direct titration 2. Back titration 3. Replacement titration
Ways of Performing Titration
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Direct titration
the analyte reacts with the standard solution directly.
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Back titration
an excess standard solution is added and the excess is determined by the addition of another standard solution.
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Replacement titration
the analyte is converted to a product chemically related to it and the product of such reaction is titrated with a standard solution.
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1. Loss of sample 2. Contamination on dilution of solution 3. Faulty mixing of solution after they have been diluted. 4. Impurities in the primary standard 5. Errors in weighing. 6. Use wrong indicators for titration 7. Poor change from buret or pipet
SOURCES OF ERROR IN TITRIMETRIC OPERATION
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Neutralization Titrations
It is a chemical reaction in which an acid and a base react quantitatively with each other.
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Neutralization Titrations
It is used to monitor the progress of reactions that produce or consume hydrogen ions
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Acid base equilibria
ubiquitous in both chemistry and science in general.
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Standard solutions of strong acid and strong bases
used extensively for determining analytes that are themselves acids or bases or that can be converted to such species by chemical treatment.
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strong acids or strong bases
The standard solution used in neutralization titrations are
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• Nitric acid
seldom used because its oxidizing properties offer the potential for undesirable side reaction.
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Determinate error
occurs when the pH at which the indicator changes color differs from the pH at the equivalence point. It can usually be minimized by choosing the indicator carefully or by making a blank correction.
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Indeterminate error
originates from the limited ability of the eye to distinguish reproducibly the intermediate color of the indicator.
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a) Temperature b) lonic strength of the medium c) Presence of the organic solvents and colloidal particle
Variables that Influence the Behavior of Indicators
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a) The reaction of acid with water b) The dissociation of water itself
The hydronium ion in an aqueous solution of a strong acid has two sources:
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BACK TITRATION
a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent
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1. React with the excess volume of reactant 2. 3. the reaction can reach the completion quickly 4. an indirect titration procedure 5. the proportion consumed in the reaction of back titration being obtained by difference
Properties of back-titration
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1. The analyte may be in solid form 2. The analyte may contain impurities 3. The analyte reacts slowly with titrant in direct or forward titration 4. Weak acid – weak base reactions can be subjected to back titration for analysis of solution of unknown concentration.
Possible reasons for devising back titration technique are
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QUALITATIVE CHEMISTRY
This is the determination of the chemical composition of a sample. It encompasses a set of analytical chemistry techniques that provide nonnumerical information about a specimen.
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second half of the nineteenth century
The history of analysis of petroleum and its products can only be suggested to have started during the _____
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elemental composition
One important aspect of petroleum analysis is the _____
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Hydrocarbons
molecules that are formed by the union of carbon and hydrogen atoms
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2% 1%
Crude oil can contain up to _% oxygen and _% nitrogen.
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Sulfur
_____ in crude oil give the oil a distinctive sour odor.
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sour crude
If a crude contains high levels of sulfur, it is called a _____
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sweet crude
if it has little or no sulfur it is called
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Refining
the process of converting crude oil into high value products.
process by which crude is separated into two or more components based on some physical property, usually boiling point
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Hydrotreating
process of improving the quality of a material by using chemical reactions to remove compounds present in trace amounts that give the material the undesired quality.
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Catalytic cracking and Hydrocracking
rocesses which fundamentally change the molecular structure of the feedstock, usually by "cracking" large molecules into small ones
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Combining
process which takes the small molecules and recombines them in the presence of a catalyst to convert them into high octane gasoline.
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Rearranging
at the catalytic reformers, gasoline is rearranged and changed to give it the high octane.
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Crude Distillation Unit
the primary process in a refinery
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Crude Distillation Unit
physical separation of the main groups of hydrocarbon molecules carried out in a distillation unit
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Reforming Unit
The reforming process actually removes hydrogen from low-octane gasoline. The hydrogen is used throughout the refinery in various cracking (hydrocracking) and treating (hydrotreating) units
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a. Platinum b. Rhenium
two Precious metal catalyst
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Alkylation Units
This process takes the small molecules and recombines them in the presence of sulfuric acid catalyst to convert them into a high octane gasoline.
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Refinery Flare
To protect the environment, excess gas in the distillation of crude is being burned at the flare
Distillation Fractions with Boiling temperatures 350 °C +
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Heavy Gas Oil
Distillation Fractions with Boiling temperatures 300 °C - 350 °C
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Light Gas Oil
Distillation Fractions with Boiling temperatures 240 °C - 300 °C
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Kerosene
Distillation Fractions with Boiling temperatures 180 °C - 240 °C
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Light Naphtha
Distillation Fractions with Boiling temperatures 100 °C - 180 °C
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Composition
to ensure uniform quality
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Composition
to calculate physical properties like density, vapor pressure and motor octane number
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Vapor Pressure
to select proper containers for safe handling of the material to measure the amount of most volatile material
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Vapor Pressure
an indirect measure of the most extreme low temperature conditions when initial vaporization can be expected to occur
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Copper Strip
to ensure that material will not cause deterioration of copper and copper alloy fittings
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Sulfur
- to meet government regulations - to prevent poisoning of catalyst - to ensure that product will not cause immediate corrosion of metal surfaces
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Octane
-correlates with anti-knock performance of an engine under mild operating conditions - used by engine manufacturers as primary specification measurement related to matching fuels and engine
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Aromatics Benzene MTBE
- for regulatory compliance : Clean Air Act - for process control - for quality assurance
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Flash Point
measures and describes the properties of the sample in response to heat and flame under controlled lab conditions
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Flash Point
used in shipping, storage, handling and safety regulations to define “flammable” and “combustible”
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Color
- to meet government specification - to detect contamination of product
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Density
- for converting volume to weight - an important quality indicator - can be used to determine contamination
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Lubricity
May be used to evaluate the relative effectiveness of diesel fuels for preventing wear under prescribed test conditions
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Viscosity
Important for the estimation of optimum storage, handling and operational conditions
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Freezing point
to detect the lowest temperature at which the fuel remains free of solid hydrocarbon crystals that can restrict the flow of fuel through the filters of an aircraft engin
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REPEATABILIT
“Duplicate results obtained by the same operator should be considered suspect if they differ (from each other) by more than r”
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REPRODUCIBILITYY
“Results submitted by each of two laboratories should be considered suspect if they differ (from each other) by more than R”
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Density Test methods ASTM D1298 / D5002
Precision Details r (repeatability) r = 0.0005 kg/L R(Reproducibility) R = 0.0012 kg/L
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Kinematic Viscosity Test methods ASTM D445
Used to ensure liquid flow is matched to pumps and lines. Viscosity gives an indication of boiling range and composition.
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Kinematic Viscosity Test methods ASTM D445
Used to determine the restriction to flow at specific temperatures.
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Reid vapour Pressure Test methods ASTM D323
The maximum vapour pressure is limited by the storage and handling equipment. ships cannot carry crude with a True Vapour Pressure of greater than 86 KPa (12.5 psi).