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VOLUMETRIC ANALYSIS
INTRODUCTION
Volumetric analysis is an aspect of quantitative analysis which involves the measurement of the volume of reacting solutions in order to find the masses of substances dissolved in them.in other words, two solutions are given; one is a solution of an acid and other a solution of a base .one of them is a standard solution and you are required, by titration to standardize the other.
The other aspect of quantitative analysis is gravimetric analysis, which involves weighing and determining the masses of reactants and products of a chemical reaction.
The most popular aspect of Volumetric analysis is the acid – base (neutralization) reactions. The technique of determination is by titration. Other aspects are redox and precipitation reaction.
APPARATUS USED IN VOLUMETRIC ANALYSIS ARE:
The burette, pipette, beaker, flasks, funnel, wash bottle, chemical balance, dropping pipette and retort stand.
Basic definitions in volumetric analysis
I.TITRATION: It is the technique for carrying out volumetric analysis.
II.CONCENTRATION: The concentration of a solution is the amount of solute in a given volume of the solution.
III.STANDARD SOLUTION: It is a solution containing a known amount of solute in a known volume of solution. An example of a standard solution is a molar solution.
IV.MOLAR SOLUTION: It is a solution which contains one mole of solute in 1dm3solution.
V.BUFFER SOLUTION: It is a solution which resists a change in pH or H+upon further addition of acid or alkali. Buffers are usually made of solutions of a weak acid and its conjugate base or a weak base and its conjugate acid. The weak acid usually has a pH value lower than 7 and is therefore used to buffer systems in the basic region. Examples of buffers solution and their pH ranges over which they are effective are given below:
| BUFFER SYSTEM | PH RANGE |
| Ethanoic acid/Sodium ethanoate (CH3COOH/CH3COONA) | 4.25-5.25 |
| Trioxocarbonate(iv) (carbonic) acid/Sodium hydrogentrioxocarbonate | 5.87-6.87 |
| Ammonia/Ammonium chloride (NH3/NH4Cl) | 8.75-9.75 |
| Sodiumtrioxocarbonate / sodiumhydrogentrioxocabonate | 9.75-10.75 |
MOLAR MASS: This is the mass of one mole of a substance expressed in grams. Its unit is gram per mole.
END POINT: This is the point at which the chemical reaction is complete during titration. The end point is detected with the help of an indicator.
INDICATORS: These are weak organic acids or bases whose colors change with pH of the solution. Indicators are widely used in monitoring titration involving colorless solutions of acids and bases.
DIFFERENT INDICATORS AND THEIR COLOURS IN DIFFERENT MEDIA
| INDICATOR | COLOUR IN ACIDIC MEDIUM | COLOUR IN ALKALINE MEDIUM | COLOUR AT END POINT |
| Methyl Orange | Pinkish red | yellow | Orange |
| Phenolphthalein | Colorless | red | colorless |
| Litmus | Red | blue | Pink/purple |
| Methyl red | Pink | yellow | orange |
| Screened methyl orange | Purple(violet) | green | grey |
| Bromothymol blue | Yellow | blue | green |
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