Theory Of Determining Moisture Content Biology Essay

It is of import that the H2O content of both natural and finished goods be determined at all phases of the fabrication procedure since the quality of the merchandise depends on it. The presence of unwanted wet in merchandises such as kerosine, transformer insularity oil and brakes oil, can hold black effects.In the pharmaceutical industry, it is of import to cognize the sum of H2O nowadays in the active ingredients of a drug in order to right foretell its life-time, stableness and effectivity. In the nutrient industry, the H2O content of both natural stuffs and the finished grocery demands to be carefully monitored. The technique most normally used for these analyses is the Karl Fischer titration.

This titration is based upon the oxidization of sulfur dioxide by I in the presence of H2O.

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Theory of finding wet content

Titration

This is a technique used to find the concentration of a substance in solution by adding to it a standard reagent of known concentration in carefully measured sums until a reaction of definite and known proportion is completed, as shown by a colour alteration or by electrical measuring, and so ciphering the unknown concentration.

What is Karl-Fischer titration?

Karl Fischer is an analytical technique designed to mensurate the water/moisture content in solids, liquids or gaseous substances. It involves the reaction of H2O, I and sulfur dioxide in the presence of an intoxicant such as methyl alcohol and an organic base such as anhydrous pyridine.Chemical reaction 1: CH30H + SO2 +RN – [ RNH ] SO3CH3Chemical reaction 2: [ RNH ] SO3CH3 + I2 + H2O + 2RN – [ RNH ] SO4CH3 + 2 [ RNH ] IThe first reaction involves the formation of the akylsulfite intermediate. In the 2nd reaction, the akylsulfite reacts with the H2O and I.In the 2nd reaction, H2O and I are used up in equimolar sums. As such, if the sum of I consumed is known, so the sum of H2O nowadays in the sample will besides be known.

Types of Karl-Fisher titration

Volumetric titration: In the volumetric titration method the I is present within the reagent. Iodine, required for reaction with H2O, is antecedently dissolved in H2O, and the H2O content is determined by mensurating the sum of I consumed as a consequence of reaction with H2O in a sample. Volumetric titration is used in samples incorporating 0.

1 % – 100 % of H2O. The volumetric system is used for the titration of solids, liquids and gases and it allows for the alteration of temperature.Coulometric titration: In the coulometric titration method, the I is produced at an electrode. Iodine is generated by the electrolysis of the reagent incorporating iodide ion, and so, the H2O content in a sample is determined by mensurating the measure of electricity which is required for the electrolysis ( the production of I ) , based on the quantitative reaction of the generated I with H2O. Coulometric titration is used in samples incorporating 0.001 % – 0.1 % of H2O. The coulometric system is used for the titration of liquids and gases and has no option for the alteration of temperature.

Both methods use bi-potentiometric titration to mensurate the sum of I consumed by the H2O.Bi-potentiometric titration: is a technique designed to track the extent of a reaction by mensurating the alterations in electrical conduction of the reaction solution.

Bi-potentiometric titration: finding the sum of I

See the 2nd reaction that occurs in Karl Fischer titration:[ RNH ] SO3CH3 + I2 + H2O + 2RN – [ RNH ] SO4CH3 + 2 [ RNH ] IThis is a redox reaction since both oxidization and decrease is happening. The sulfur in the akylsulfite has been oxidized and the I has been reduced.Oxidation reaction: SO3CH32- ® SO4CH32- + 2e- reduction agentDecrease reaction: I2 + 2e- ® 2I- ( E & A ; deg ; = 0.54 V ) oxidising agentFrom the two oxidization and decrease equations, it can be seen that sulfur has changed oxidization province from +4 to +6 whereas I has moved from O to -1.

As such, alkylsulfite is the cut downing agent and I is the oxidising agent.The decrease of iodine causes iodine to take up negatrons produced by the oxidization of S, and this causes a alteration in the electrical potency of the system. The alteration in possible is detected by an electrode called the dual Pt electrode ) .

Practice of finding wet content

Volumetric method

Apparatus: Automatic burette, titration flask, back-titration flask, scaremonger, equipment for bi-potentiometric titrationReagents: sulfuric acid, H2O, I, menthanol and pyridine.Procedure: Direct titrationMeasure 25ml of methyl alcohol for H2O finding and topographic point in a dried titration flask.

Titrate with H2O finding TS ( a reagent ) to the terminal point.Accurately weigh a measure of the sample incorporating 10 to 50mg of H2O so reassign it rapidly into the titration flask, and fade out by stirring.Titrate the solution with H2O finding TS to the terminal point under vigorous stirring. When the sample is indissoluble in the dissolver, pulverize the sample rapidly, accurately weigh a suited sum of the sample, and reassign it rapidly into the titration vas, stir the mixture for 30 proceedingss while protecting it from wet.

Perform a titration under vigorous stirring. When the sample interferes with the Karl Fisher reaction, H2O in the sample can be removed by heating under a watercourse of N gas and introduced into the titration vas by utilizing a water-evaporation device.Water =

Back titration

Take 20ml of methyl alcohol for H2O finding in the dried titration vas, and titrate with H2O finding TS.Accurately weigh a suited measure of the sample incorporating 1050 milligram of H2O, reassign the sample rapidly into the titration vas, add an inordinate and definite volume of H2O finding TS.

Stir for 30mins, protecting from atmospheric wet, and so titrate the solution with WaterMethanol Standard Solution under vigorous stirring.Where: degree Fahrenheit = the figure of milligram of H2O ( H2O ) matching to 1 milliliter of H2O finding TS,f* = the figure of milligram of H2O ( H2O ) in 1 milliliter of WaterMethanol Standard Solution

Coulometric method

Apparatus: An electrolytic cell for the production of I, a scaremonger, titration flask and a potentiometric titration system.Reagents: sulfuric acid, H2O, I, menthanol and pyridine.Procedure: 1. Take a suited volume of an anolyte for H2O finding in a titration vas.2. Immerse in this solution a brace of dual Pt electrodes for potentiometric titration at changeless current.

3. Then, plunge the iodide production system filled with a catholyte for H2O finding in the anolyte solution.4. Switch over on the electrolytic system and do the content of the titration vas anhydrous.

5. Following, take an accurately weighed sum of the sample incorporating 15mg of H2O, add it rapidly to the vas, and fade out by stirring.6. Perform the titration to the terminal point under vigorous stirring.7.

When the sample is indissoluble in the anolyte, pulverize it rapidly, and add an accurately weighed sum of the sample to the vas.8. After stirring the mixture for 530 proceedingss, while protecting from atmospheric wet, execute the titration with vigorous stirring.9. Determine the measure of electricity ( C ) [ electric current ( A ) – clip ( s ) ] required for the production of I during the titration, and cipher the per centum H2O content in the sample.

When the sample interferes with the Karl Fisher reaction, H2O in the sample can be removed by heating under a watercourse of N gas, and introduced into the titration vas by utilizing a water-evaporation device.

Precaution ( s )

Because H2O finding TS ( a reagent ) is highly hygroscopic, the titration setup should be protected from atmospheric wet. For this ground, silicon oxide gel or Ca chloride for H2O finding is normally used for wet protection.

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