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A Quantitative And Chemical Analysis Of Titration Biology Essay

In the social sciences, quantitative research refers to the systematic empirical investigation of quantitative properties and phenomena and their relationships. The objective of quantitative research is to develop and employ mathematical models, theories and/or hypotheses pertaining to phenomena...

 chemical analysis

Analytical chemistry

Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...

 that is used to determine the unknown concentration

Concentration

In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent.To...

 of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis.

A reagent

Reagent

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction or is added to see if a reaction occurs". Such a reaction is used to confirm the presence of another substance...

, called the titrant or titrator, of a known concentration (a standard solution

Standard solution

Standard solution is a chemical term which describes a solution of known concentration. The concentration of the solution is normally expressed in units of moles per Liter...

) and volume

Volume

Volume is how much three-dimensional space a substance or shape occupies or contains,often quantified numerically using the SI derived unit, the cubic metre. The volume of a container is generally understood to be the capacity of the container, i. e...

 is used to react with a solution of the analyte

Analyte

An analyte is a substance or chemical constituent that is determined in an analytical procedure, such as a titration. For instance, in an immunoassay, the analyte may be the ligand or the binder, while in blood glucose testing, the analyte is glucose...

 or titrand, whose concentration is not known. Using a calibrated burette

Burette

A burette is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as a titration...

 to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by an indicator (see below). This is ideally the same volume as the equivalence point

Equivalence point

The equivalence point, or stoichiometric point, of a chemical reaction occurs during a chemical titration when the amount of titrant added is stoichiometrically equal to the amount of analyte present in the sample: the smallest amount of titrant that is sufficient to fully neutralize or react with...

—the volume of added titrant at which the number of moles

Mole (unit)

The mole is the SI base unit of amount of substance, one of a few units used to measure this physical quantity. The name "mole" is an 1897 translation of the German Mol, coined by the chemist Wilhelm Ostwald in 1893, although the related concept of equivalent mass had been in use at least a...

 of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). In the classic strong acid-strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution takes on a persisting solid color as in the pink of phenolphthalein indicator

PH indicator

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions...

. There are however many different types of titrations (see below).

Many methods can be used to indicate the endpoint of a reaction; titrations often use visual indicators (the reactant mixture changes color). In simple acid-base titration

Acid-base titration

An acid-base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid/base with an acid or base of known concentration. This allows for quantitative analysis of the concentration of an unknown acid or base solution...

s a pH indicator may be used, such as phenolphthalein

Phenolphthalein

Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Often used in titrations, it turns colorless in acidic solutions and pink in basic solutions...

, which becomes pink when a certain pH (about 8.2) is reached or exceeded. Another example is methyl orange

Methyl orange

Methyl orange is a pH indicator frequently used in titrations.It is often used in titrations because of its clear colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids...

, which is red in acids and yellow in alkali solutions.

Not every titration requires an indicator. In some cases, either the reactants or the products are strongly colored and can serve as the "indicator". For example, a redox titration

Redox titration

Redox titration is a type of titration based on a redox reaction between the analyte and titrant.Redox titration may involve the use of a redox indicator and/or a potentiometer.-Example:...

 using potassium permanganate

Potassium permanganate

Potassium permanganate is the inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4– ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent...

 (pink/purple) as the titrant does not require an indicator. When the titrant is reduced, it turns colorless. After the equivalence point, there is excess titrant present. The equivalence point is identified from the first faint persisting pink color (due to an excess of permanganate) in the solution being titrated.

Due to the logarithmic nature of the pH curve, the transitions are, in general, extremely sharp; and, thus, a single drop of titrant just before the endpoint can change the pH significantly—leading to an immediate colour change in the indicator. There is a slight difference between the change in indicator color and the actual equivalence point of the titration. This error is referred to as an indicator error, and it is indeterminate.

History and etymology

The word "titration" comes from the Latin word titulus, meaning inscription or title. The French word titre, also from this origin, means rank. Titration, by definition, is the determination of rank or concentration of a solution with respect to water with a pH of 7 (which is the pH of pure H2O under standard conditions).

The origins of volumetric analysis are in late-18th-century French chemistry. Francois Antoine Henri Descroizilles developed the first burette (which looked more like a graduated cylinder) in 1791. Joseph Louis Gay-Lussac

Joseph Louis Gay-Lussac

Joseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries.- Biography :Gay-Lussac was born at...

 developed an improved version of the burette that included a side arm, and coined the terms "pipette

Pipette

A pipette is a laboratory instrument used to transport a measured volume of liquid.-Use and variations:Pipettes are commonly used in molecular biology as well as medical tests...

" and "burette

Burette

A burette is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as a titration...

" in an 1824 paper on the standardization of indigo solutions. A major breakthrough in the methodology and popularization of volumetric analysis was due to Karl Friedrich Mohr

Karl Friedrich Mohr

Karl Friedrich Mohr was a German chemist famous for his early statement of the principle of the conservation of energy. Ammonium iron sulfate, 2Fe2.6H2O, is named Mohr's salt after him.-Life:Mohr was born in 1806 into the family of a prosperous druggist in Koblenz...

, who redesigned the burette by placing a clamp and a tip at the bottom, and wrote the first textbook on the topic, Lehrbuch der chemisch-analytischen Titrirmethode (Textbook of analytical-chemical titration methods), published in 1855.

Preparing a sample for titration

In a titration, both titrant and analyte are required to be in a liquid (solution) form. If the sample is not a liquid or solution, the samples must be dissolved. If the analyte is very concentrated in the sample, it might be useful to dilute the sample.

Although the vast majority of titrations are carried out in aqueous solution, other solvents such as glacial acetic acid

Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid that gives vinegar its sour taste and pungent smell. It is a weak acid, in that it is only a partially dissociated acid in an aqueous solution...

 or ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a powerful psychoactive drug and one of the oldest recreational drugs. It is best known as the type of alcohol found in alcoholic beverages and thermometers...

 (in petrochemistry

Petrochemistry

Petrochemistry is the branch of chemistry that studies the transformation of crude oil and natural gas into useful products and raw materials.- External links :* *...

) are used for special purposes.

A measured amount of the sample can be given in the flask and then be dissolved or diluted. The mathematical result of the titration can be calculated directly with the measured amount. Sometimes the sample is dissolved or diluted beforehand, and a measured amount of the solution is used for titration. In this case the dissolving or diluting must be done accurately with a known coefficient

Coefficient

In mathematics, a coefficient is a multiplicative factor in some term of an expression ; it is usually a number, but in any case does not involve any variables of the expression...

 because the mathematical result of the titration must be multiplied with this factor.

Many titrations require buffering to maintain a certain pH

PH

In chemistry, pH is a measure of the acidity or basicity of a solution. It approximates but is not equal to p[H], the negative logarithm of the molar concentration of dissolved hydronium ions ; a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration...

 for the reaction. Therefore, buffer solution

Buffer solution

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a...

s are added to the reactant solution in the flask to maintain the pH of the solution.

Some titrations require "masking" of a certain ion. This can be necessary when two reactants in the sample would react with the titrant and only one of them must be analysed, or when the reaction would be disturbed or inhibited by this ion. In this case another solution is added to the sample, which "masks" the unwanted ion (for instance by a weak binding with it or even forming a solid insoluble substance with it).

Some redox

Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed....

 reactions may require heating the solution with the sample and titration while the solution is still hot, in order to increase the reaction rate

Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular reaction is intuitively defined as how fast a reaction takes place...

. For instance, the oxidation of certain oxalate solutions requires heating the solution to approximately 60 degrees in order to maintain a reasonable rate of reaction.

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