Volumetric Analysis

Volumetric analysis

Volumetric analysis

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.

Jean-Baptiste-Andre-Dumas

The first method of Volumetric Analysis was devised and found by the French chemist

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

Titration

A quick, accurate and widely-used way of measuring the amount of a substance in a solution.

Titrants

Standard solution with known concentration needed to react with an unknown quantity of a second substance.

Stoichiometric reaction

Reaction with definite whole number ratio between a and b

Endpoint

An abrupt change in some physical and chemical property of the sample solution

Endpoint

The point at which some detection technique tells you that chemical equivalence has been reached.

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.

Indicator

It shows the endpoint of the titration, usually by change of color, and the endpoint and equivalence point should coincide.

Standard solution

It is a solution of known concentration.

Standardization

It is a process of determining the concentration of an unknown solution.

Primary Standard

It is a substance used for standardization.

equivalence point

a theoretical point reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample.

titration error

The difference in volume or mass between the equivalence point and the end point

Indicators

often added to the analyte solution to produce an observable physical change (the end point) at or near the equivalence point.

• Colorimeters • Turbidimeters • Temperature monitors • Refractometers • Voltmeters • Current meters • Conductivity meters

Instruments Used in Measuring End Points

primary standard

a highly purified compound that serves as a reference material in volumetric and mass titrimetric methods

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:

By standardization, in which the titrant to be standardized is used to titrate

play a central role in all titrimetric methods of analysis

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

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).

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.

PRECIPITATION/SATURATION

A substance is titrated by precipitating it with a standard solution of precipitating agent.

COMPLEX FORMATION

A substance is titrated with a standard reagent to a formation of a complex

1. NEUTRALIZATION

2. OXIDATION-REDUCTION (REDOX)

3. PRECIPITATION/SATURATION

4. COMPLEX FORMATION

PROCESSES IN VOLUMETRIC ANALYSIS (By Reaction Type)

1. Spectrophotometric

2. Electrochemica

3. pH

PROCESSES IN VOLUMETRIC ANALYSIS (By Indicator)

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

Electrochemica

Is used to sense the presence or change in concentration of the oxidized and reduced forms of a redox couple

pH

• are weak acids that exist as natural dyes and indicate the concentration of H+ (H3O+) ions in a solution via color change.

1. Direct titration

2. Back titration

3. Replacement titration

Ways of Performing Titration

Direct titration

the analyte reacts with the standard solution directly.

Back titration

an excess standard solution is added and the excess is determined by the addition of another standard solution.

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.

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

Neutralization Titrations

It is a chemical reaction in which an acid and a base react quantitatively with each other.

Neutralization Titrations

It is used to monitor the progress of reactions that produce or consume hydrogen ions

Acid base equilibria

ubiquitous in both chemistry and science in general.

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.

strong acids or strong bases

The standard solution used in neutralization titrations are

• Nitric acid

seldom used because its oxidizing properties offer the potential for undesirable side reaction.

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.

Indeterminate error

originates from the limited ability of the eye to distinguish reproducibly the intermediate color of the indicator.

a) Temperature b) lonic strength of the medium c) Presence of the organic solvents and colloidal particle

Variables that Influence the Behavior of Indicators

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:

BACK TITRATION

a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent

1. React with the excess volume of reactant

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

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

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.

second half of the nineteenth century

The history of analysis of petroleum and its products can only be suggested to have started during the _____

elemental composition

One important aspect of petroleum analysis is the _____

Hydrocarbons

molecules that are formed by the union of carbon and hydrogen atoms

2% 1%

Crude oil can contain up to _% oxygen and _% nitrogen.

Sulfur

_____ in crude oil give the oil a distinctive sour odor.

sour crude

If a crude contains high levels of sulfur, it is called a _____

sweet crude

if it has little or no sulfur it is called

Refining

the process of converting crude oil into high value products.

1. Separation processes

2. Upgrading processes

3. Conversion processes

The three basic categories of Refining are:

Distillation

process by which crude is separated into two or more components based on some physical property, usually boiling point

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.

Catalytic cracking and Hydrocracking

rocesses which fundamentally change the molecular structure of the feedstock, usually by "cracking" large molecules into small ones

Combining

process which takes the small molecules and recombines them in the presence of a catalyst to convert them into high octane gasoline.

Rearranging

at the catalytic reformers, gasoline is rearranged and changed to give it the high octane.

Crude Distillation Unit

the primary process in a refinery

Crude Distillation Unit

physical separation of the main groups of hydrocarbon molecules carried out in a distillation unit

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

a. Platinum b. Rhenium

two Precious metal catalyst

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.

Refinery Flare

To protect the environment, excess gas in the distillation of crude is being burned at the flare

LPG

Product: ______ Components:Propane Critical Tests: Composition,Vapor Pressure, Copper Strip, Sulfur

MOGAS

Product: ______ Components:Velocity, Premium, Unleaded Critical Tests: Octane, Aromatics Benzene MTBE, Density, Vapor Pressure, COLOR

JET A1

Product: _____ Components: Kerosene Critical Tests: Freezing Point, Density, Color

Diesel

Product: _______ Critical Tests: Flash Point, Sulfur, Density, Color, Lubricity

FUEL OIL

Product Group: ______ Products: Bunker Fuel, LPG, Aviation gasoline, Petroleum coke Critical Tests: Density, Flash Point, Sulfur, Viscosity

Residue

Distillation Fractions with Boiling temperatures 350 °C +

Heavy Gas Oil

Distillation Fractions with Boiling temperatures 300 °C - 350 °C

Light Gas Oil

Distillation Fractions with Boiling temperatures 240 °C - 300 °C

Kerosene

Distillation Fractions with Boiling temperatures 180 °C - 240 °C

Light Naphtha

Distillation Fractions with Boiling temperatures 100 °C - 180 °C

Composition

to ensure uniform quality

Composition

to calculate physical properties like density, vapor pressure and motor octane number

Vapor Pressure

to select proper containers for safe handling of the material to measure the amount of most volatile material

Vapor Pressure

an indirect measure of the most extreme low temperature conditions when initial vaporization can be expected to occur

Copper Strip

to ensure that material will not cause deterioration of copper and copper alloy fittings

Sulfur

• to meet government regulations

• to prevent poisoning of catalyst

• to ensure that product will not cause immediate corrosion of metal surfaces

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

Aromatics Benzene MTBE

• for regulatory compliance : Clean Air Act

• for process control

• for quality assurance

Flash Point

measures and describes the properties of the sample in response to heat and flame under controlled lab conditions

Flash Point

used in shipping, storage, handling and safety regulations to define “flammable” and “combustible”

Color

• to meet government specification

• to detect contamination of product

Density

• for converting volume to weight

• an important quality indicator

• can be used to determine contamination

Lubricity

May be used to evaluate the relative effectiveness of diesel fuels for preventing wear under prescribed test conditions

Viscosity

Important for the estimation of optimum storage, handling and operational conditions

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

REPEATABILIT

“Duplicate results obtained by the same operator should be considered suspect if they differ (from each other) by more than r”

REPRODUCIBILITYY

“Results submitted by each of two laboratories should be considered suspect if they differ (from each other) by more than R”

Density Test methods ASTM D1298 / D5002

Precision Details r (repeatability) r = 0.0005 kg/L R(Reproducibility) R = 0.0012 kg/L

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.

Kinematic Viscosity Test methods ASTM D445

Used to determine the restriction to flow at specific temperatures.

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).