Prelim

Titrimetric Analysis

known as volumetric analysis

Titrimetric Analysis

Volume of a solution of known concentration consumed during an analysis is taken as a measure of the amount of active constituent in a sample being analyzed.

Analyte or active constituents

chemical substances being analyzed.

Titrant

solution of known concentration usually added by means of a buret.

Indicator

a chemical which changes color at or very near the point in the titration where equivalent quantities of analyte and titrant have reacted.

Stoichiometric point or equivalence point

theoretical point at which equivalent amounts of a titrant and analyte have reacted

End point

Stop at some point at which there occurs a sudden change in some property of the reaction mixture.

Gram-equivalent weight (GEW) or gram-equivalent of a chemical

weight in grams which is chemically equivalent to 1 gram-atom of hydrogen (1.0079 g).

- In neutralization reactions it is defined as that weight of a substance in grams which (1) contains, (2) furnishes, (3) reacts with direct or indirectly, or (4) replaces as gram-atom or ion of hydrogen

EQUIVALENT (EQUIV)

the number of gram-equivalents involved in a quantitative procedure.

MILLIEQUIVALENT (MEQ)

the number of gram-mill equivalents involved in a quantitative procedure

NORMALITY

the number of equivalents of solute per liter (equiv/liter) or milliequivalent per milliliter (meq/ml) of a solution

MOLARITY

expression of the concentration of a solution in terms of moles per liter.

STANDARDIZATION

determination of the normality or molarity of a solution

PRIMARY STANDARD

• the use of carefully weighed sample of a substance of known purity.

• highest purity

• 100% purity

SECONDARY STANDARD

the use of another standard solution.

Titer

weight of a substance chemically equivalent to 1ml of a standard solution

Direct titrimetric methods

the reaction must be rapid so as end point is discernible.

INDICATORS

• are complex organic compounds use

• determine the end point in neutralization processed

• determine hydrogen-ion concentrations pH, or

• indicate that a desired change in pH has been affected.

MIX INDICATORS

used to sharpen up the color change

Theory: Physicochemical

• attributes the color of certain ions , an increase in which causes the appearance of a new color

• a decrease in which causes the disappearance of a color or appearance of a diff color.

• if nagiba amt., magiba din color

Organic Theory

• attributes the color of indicator to certain groupings of the elements in a compound and the change in color to a change in molecular structure.

• if iba chemical structure, maiba din yung color

Theory: Colloidal

assumes that indicator form colloidal solutions the change in color of which is dependent upon change in size of the colloidal particle

methyl orange, methyl red, or phenolphthalein

Strong acid titrate w/ Strong alkali OR Strong alkali w/ Strong acid

phenolphthalein

Weak Acid titrate w/ Strong Alkali

methyl red

Weak Alkali titrate w/ Strong Acid

Weak Acid & Weak Alkali

Should never be titrated since NO indicator would give sharp end point.

4.2-6.2

pH of Methyl Red

8-10

pH of Phenolphthalein

0-2

pH of Malachite green

Red to Yellow (RY)

Color of Methyl Red (Acid to Base)

Colorless to Red (CR)

Color of Phenolphthalein (Acid to Base)

Yellow to Green (YG)

Color of Malachite Green (Acid to Base)

Acidimetric Analysis: Direct Titration

• conducted by introducing a standard acid solution gradually from a burette into a solution of the base being assayed until chemically equivalent amounts of each have reacted as shown by some change in properties of the mixture.

Acidimetric Analysis: Residual Titration

• known as Back Titration

• reactions are slow

• when the substance to be assayed does not give a distinct, sharp end point with an indicator by direct titration

Titration: Assay of Sodium Bicarbonate

Direct Titration

Titration: Assay of Zinc Oxide & Assay of Milk of Magnesia

Residual Titration

Methyl Orange

Indicator: Assay of Sodium Bicarbonate & Zinc Oxide

as most indicators are affected by the carbonic acid liberated in the reaction, which causes a change in color before the reaction is complete.

why methyl orange is used as indicator in assay of sodium bicarbonate (Direct Titration)

Na2SO4 + 2H2O + 2CO2

2NaHCO3 + H2SO4 =

for carbon dioxide to be released thus would not form carbonic acid

why do we need to heat the soln. in assay of sodium bicarbonate (direct titration)

1N H2SO4 & 1N NaOH

Titrant: Assay of Zinc Oxide (Residual Titration)

40.68 mg

Titer Value of Zinc Oxide (ZnO)

Factor of Zinc Oxide

2

ZnO + 2NH4Cl =

ZnCl2 + N3 + H2O

Yellow to Red (Base to Acid)

End Point of Sodium Bicarbonate

Pink to Yellow (excess NaOH) (Acid to Base)

End Point of Zinc Oxide

Indicator: Assay of Milk of Magnesia (Residual Titration)

Methyl Red

End Point: Assay of Milk of Magnesia (Residual Titration)

Red to Yellow (Acid to Base)

Factor of Mg(OH)2

2

Nitrogen Determination by Kjeldahl Method

• Nitrogen to ammonia = ammonia to distillation then titrate

• DDT (digestion, distillation & titration)

• Method 1 & Method II

Method I: Nitrogen Determination by Kjeldahl Method

• 1g of sample is used

• a macro method in which the ammonia is distilled into excess boric acid solution

• used is nitrates or nitrites are not present

Method II: Nitrogen Determination by Kjeldahl Method

• 2-3 mg of sample is used

• a semi micromethod in which smaller samples are employed using a semi micro Kjeldahl apparatus.

• nitrogen is first liberated by acid digestion

Alkalimetric Analysis

titrant; base and the analyte; acid

methyl red and phenolphthalein

used as indicators in most inorganic acid

frequently used indicator in organic acids.

phenolphthalein

thymol blue, bromothymol blue and thymolphthalein

employed as indicator in organic acids

Alkalimetric Analysis: Direct Methods

Assay of Hydrochloric Acid

Assay of Hydrochloric Acid

• Official requirement for concentrated HCl 36.5% - 38%.

• Official requirement for diluted HCl is 9.5g– 10.5g/100 mL

Blank Determination

• without analyte, needed to lessen titration error.

• reacts too slowly with the titrant because of poor solubility.

Titration Method: Residual with Blank

Assay of Aspirin

Assay of Aspirin

• Official requirement is 99.5% - 100.5%

• Titrated with NaOH to neutralize any free acid formed by hydrolysis

  of the acetylsalicylic acid

salicylic acid + acetic acid

Acetylsalicylic acid + H2O=

sodium salicylate + sodium acetate

sodium acetyl salicylate + NaOH=

Methylparaben (MP)

Used in pharmacy as a preservative in pharmaceutical preparations. From the following procedure and experimental data, calculate the percent purity of a sample of this material.

Non-aqueous Titrimetric Analysis

• used when the substance to be assayed is poorly soluble in water.

• moisture content should be held to less than 0.05% so as not to have any appreciable effect on the end point

Advantages of Non-aqueous Titrimetric Analysis

• the disadvantage of poor solubility and weak reactivity with water were overcome.

• Simplicity, speed, precision, and accuracy are equivalent to those of the classical procedure

Disadvantages of Non-aqueous Titrimetric Analysis

• moisture is to be avoided, since H2O, being weakly basic, would compete with the weak nitrogen base for the HClO4 and the sharpness of the end point would be lost.

• Greater care in the control of temperature during the standardization, and analysis procedures is necessary

Neutral solvents– such as acetonitrite, alcohols, chloroform, benzene, dioxane, or ethyl acetate

• Solvents used in Acidimetry in Non-aqueous

• This is used as they do not enhance dissociation to any great degree.

Acidic solvents– such as formic, glacial acetic acid, and propionic acids, acetic anhydride, and sulfonyl chloride

• Solvents used in Acidimetry in Non-aqueous

• This is used for weak bases and their salts where the protogenic quality of the solvent is utilize

Perchloric acid (strong acid) in glacial acetic acid

• Titrant in Acidimetry in Non-aqueous

• the strongest of the known common acids which gives excellent results with practically all the known weak bases.

• Crystal violet

• Methylrosaniline chloride

• Quinaldine red

• Alpha-naphtholbenzein

• Malachite green

• Indicators in Acidimetry in Non-aqueous

• For Weak Bases and their salts

• Methyl red

• Methyl orange

• Thymol blue

• Indicators in Acidimetry in Non-aqueous

• For Strong Bases

• Ethylenediamine

• n-butylamine

• morpholine

• Alkalimetric in Non-aqueous Solvents

• For strong bases; titration of weak acids

• Dimethylformamide

• Pyridine

• Alkalimetric in Non-aqueous Solvents

• Weak Base Solvents; titration of medium-strength acidic substances

sodium methoxide & lithium methoxide

Titrant: Alkalimetric in Non-aqueous