Analytical Chemistry part 19 Summary PDF

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Summary

 The final reading of the buret is made at this point, and the volume of base delivered in the titration is calculated from the difference between the initial and final buret readings. The flask on the right shows what happens when a slight excess of base is added to the titration mixture. The solu...

Description

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The final reading of the buret is made at this point, and the volume of base delivered in the titration is calculated from the difference between the initial and final buret readings. The flask on the right shows what happens when a slight excess of base is added to the titration mixture. The solution turns a deep pink color, and the end point has been exceeded. In color plate 9, the color change at the end point is much easier to see than in this black-and-white version.

TITRATION ERROR (ET) 

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

Et = Vep – Veq  

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Vep : the actual volume of reagent required to reach the end point Veq: the theoretical volume to reach the equivalence point

A primary standard is a highly purified compound that serves as a reference material in all volumetric and mass titrimetric methods. The accuracy of a method is critically dependent on the properties of this compound. Important requirements for a primary standard are  High purity  Atmospheric stability  Absence of hydrate water so that the composition of the solid does not change with variation in relative humidity  Ready availability at modest cost  Reasonable solubility in the titration medium  Reasonably large molar mass so that the relative error associated with weighing the standard is minimized.

SECONDARY STANDARD 

a compound whose purity has been established by chemically analysis and that serves as the reference material for a titrimetric method

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The accuracy of a titrimetric method can be no

better than the accuracy of the concentration of

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the standard solution used in the titration. Two basic methods are used to establish the concentration of such solutions. The first is the direct method in which a carefully weighed quantity of a primary standard is dissolved in a suitable solvent and diluted to a known volume in a volumetric flask. The second is by standardization in which the titrant to be standardized is use to titrate  (1) a weighed quantity of a primary standard,  (2) a weighed quantity of a secondary standard, or  (3) a measured volume of another standard solution

TWO BASIC METHODS ARE USED CONCENTRATION OF SUCH SOLUTIONS: (1) Direct method ～ ～ careful weighed quantity of primary standard is dissolved in a suitable solvent and dilute to exactly know volume. (2) Standardization: the titrant to be standardized is used to titrate weighed quantity of a primary standard weighed quantity of a secondary standard measured volume of another standard solution

M= moles/L N= equivalents/L

SOME USEFUL ALGEBRAIC RELATIONSHIPS (VOL) 

Most volumetric calculations are based on two pairs of fundamental equations that are derived from definitions of millimole, mole, and molar concentration. For the chemical, we may write Amount (mol) = mass (grams) molar mass (gm/mole) Amount (mmol) = mass (grams) mmolar mass (gm/mmole)  We may derive a second pair from the definition of molar concentration. That is, amount (mol) = volume (L) x concentration (mole/L) amount (mmol) = volume (mL) x concentration (mmole/mL)

SOME USEFUL ALGEBRAIC RELATIONSHIPS (MASS) 

WEIGHT OR GRAVIMETRIC TITRIMETRY – Mass of titrant is measured

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The concentrations of standard solutions are generally expressed in units of either molarity c or normality cN. Molarity gives the number of moles of reagent contained in one liter of solution, Normality gives the number of equivalents of reagent in the same volume.

Weight molarity (MW) : the number of moles of reagent in 1 Kg Solution  Weight Molarity= Mole solution (Kg) Ex. 0.1 MW NaCL = 0.1 mol of the NaCl in 1 Kg of solution ...