The method was discovered by Craig and Post. It is consists of 300-400 such chambers. The organic solvent and the aqueous solution is introduced to tube A and then it passes to B. It is shaken and is allowed to attain the equilibrium. Now, the apparatus is tilted so that the upper layer gets decanted through C and is collected in D. When the apparatus is again made vertical. The liquid passes through D into E in the next chamber of A and then to B. The process is repeated till the two liquids gets almost separated.

Application:

1. With the help of this method we can have accurate quantitative analysis of a single as well as the mixture of the components.

2. In this case apparatus required are very simple (separating funnel burette pipets conical flask etc.)

3. Time required for analysis is very small.

4. The method is very well used for detection of traces quantity of substance where precipitation method (Gravimetry) is not possible.

5. Fe⁺³ ferric ion can be easily extracted by ether from 6 molar HCl solution of the ferrous ally and iron ore.

6. The extraction can also be use in the extraction of metal as metal chelate where later has high solubility in an immiscible solvent such as chloroform and benzene.

7. In industrial and commercial field extraction by counter current extraction is frequently applied in the separation of components where the difference in the distribution coefficient are small.

8. The phenomenon is widely applied in drug analysis.

9. The solvent extraction is used in clinical laboratory.

10. Metal chelates are more soluble in non-polar solvents. Thus Ni(II) in its tetra co-ordinate complex with dimethyl glyoxime can be extracted into chloroform. In presence of citrate or tartrate the precipitation of Fe(III) and Cr(III) can be avoided.

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The method was discovered by Craig and Post. It is consists of 300-400 such chambers. The organic solvent and the aqueous solution is introduced to tube A and then it passes to B. It is shaken and is allowed to attain the equilibrium. Now, the apparatus is tilted so that the upper layer gets decanted through C and is collected in D. When the apparatus is again made vertical. The liquid passes through D into E in the next chamber of A and then to B. The process is repeated till the two liquids gets almost separated.

Application:

1. With the help of this method we can have accurate quantitative analysis of a single as well as the mixture of the components.

2. In this case apparatus required are very simple (separating funnel burette pipets conical flask etc.)

3. Time required for analysis is very small.

4. The method is very well used for detection of traces quantity of substance where precipitation method (Gravimetry) is not possible.

5. Fe⁺³ ferric ion can be easily extracted by ether from 6 molar HCl solution of the ferrous ally and iron ore.

6. The extraction can also be use in the extraction of metal as metal chelate where later has high solubility in an immiscible solvent such as chloroform and benzene.

7. In industrial and commercial field extraction by counter current extraction is frequently applied in the separation of components where the difference in the distribution coefficient are small.

8. The phenomenon is widely applied in drug analysis.

9. The solvent extraction is used in clinical laboratory.

10. Metal chelates are more soluble in non-polar solvents. Thus Ni(II) in its tetra co-ordinate complex with dimethyl glyoxime can be extracted into chloroform. In presence of citrate or tartrate the precipitation of Fe(III) and Cr(III) can be avoided.

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Though the multiple extraction is more beneficial than single step extraction. For analytical chemist it is easy to find out the amount extracted in single extraction, so he follow single extraction rather than multiple extraction because it is tedious. The relation between percentage extraction (E) for single extraction can be derived as follow: We know $$ { W }_{ 1 } = \left[ \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right] \times a \qquad ...(1) $$ where \({ W }_{ 1 }\) is the weight of solute remaining after 1st extraction.
\( { V }_{ W } \)= Volume of Aqueous Phase
\( { V }_{ o } \) = Volume of Organic Phase
\(D\) = Distribution Ratio
\(a\) = Total weight of Solute present initially.

The amount extracted will be a $$ { W }_{ 1 } = a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \qquad ...(2) $$ $$ = a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) $$ $$ \therefore Percentage \ extraction \ (E) = \left( \frac { a - { W }_{ 1 } }{ a } \right) \times 100 $$ Lets Substitute the values from equation (1) $$ E = \left( \frac { a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) }{ a } \right) \times 100 $$ $$ E = \left( 1 - \left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \right) \times 100 $$ $$ E = \left( \frac { { V }_{ o }D + { V }_{ W } - { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \times 100 $$ $$E = \left( \frac { { V }_{ o }D }{ { V }_{ o }D + { V }_{ W } } \right) \times 100 $$ on dividing the numerator and denominator of RHS by \({ V }_{ o }\) we get $$ E = \left( \frac { D }{ D + \frac { { V }_{ W } }{ { V }_{ o } } } \right) \times 100 $$ $$ \therefore Percentage extraction (E) = \frac { 100D }{ D + \frac { { V }_{ W } }{ { V }_{ o } } } $$ Thus % extraction (E) depends on D as well as \(\frac { { V }_{ W } }{ { V }_{ o } } \).

Though the multiple extraction is more beneficial than single step extraction. For analytical chemist it is easy to find out the amount extracted in single extraction, so he follow single extraction rather than multiple extraction because it is tedious. The relation between percentage extraction (E) for single extraction can be derived as follow: We know $$ { W }_{ 1 } = \left[ \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right] \times a \qquad ...(1) $$ where \({ W }_{ 1 }\) is the weight of solute remaining after 1st extraction.
\( { V }_{ W } \)= Volume of Aqueous Phase
\( { V }_{ o } \) = Volume of Organic Phase
\(D\) = Distribution Ratio
\(a\) = Total weight of Solute present initially.

The amount extracted will be a $$ { W }_{ 1 } = a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \qquad ...(2) $$ $$ = a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) $$ $$ \therefore Percentage \ extraction \ (E) = \left( \frac { a - { W }_{ 1 } }{ a } \right) \times 100 $$ Lets Substitute the values from equation (1) $$ E = \left( \frac { a - a\left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) }{ a } \right) \times 100 $$ $$ E = \left( 1 - \left( \frac { { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \right) \times 100 $$ $$ E = \left( \frac { { V }_{ o }D + { V }_{ W } - { V }_{ W } }{ { V }_{ o }D + { V }_{ W } } \right) \times 100 $$ $$E = \left( \frac { { V }_{ o }D }{ { V }_{ o }D + { V }_{ W } } \right) \times 100 $$ on dividing the numerator and denominator of RHS by \({ V }_{ o }\) we get $$ E = \left( \frac { D }{ D + \frac { { V }_{ W } }{ { V }_{ o } } } \right) \times 100 $$ $$ \therefore Percentage extraction (E) = \frac { 100D }{ D + \frac { { V }_{ W } }{ { V }_{ o } } } $$ Thus % extraction (E) depends on D as well as \(\frac { { V }_{ W } }{ { V }_{ o } } \).

If a solution contains two or more solutes say A and B, it is observed that when A is extracted, some amount of B is also extracted. The extent of the seperation can be expressed in terms of one factor called Seperation Factor \(\beta\) . This is related to the distribution ratio of A and B. $$ \boxed { \beta = \frac { D_{ A } }{ { D }_{ B } } = \frac { { { C }_{ o(A) } }/{ { C }_{ a(A) } } }{ { { C }_{ o(B) } }/{ { C }_{ a(B) } } } } $$ It is ratio therefore no unit and no dimension.

The larger value is always placed in the numerator. \beta must be made as large as possible by choice of extractant and by adjusting the volume ratio.

When \(D_{ A }\) = 10 and \(D_{ B } \)= 0.1. The \(\beta = \frac { 10 }{ 0.1 } = 100%\)

single extraction in case will remove 91% of A and 9% of B. It can be obtained for A, $$ E = \left[ \frac { 100{ D }_{ A } }{ { D }_{ A } + { { V }_{ W } }/{ { V }_{ o } } } \right] $$ for $${ V }_{ W } = { V }_{ o }\qquad \qquad \therefore { { V }_{ W } }/{ { V }_{ o } } = 1 $$ $$ \therefore E = \left[ \frac { 100 \times 10 }{ 10 + 1 } \right] = \left[ \frac { 1000 }{ 11 } \right] = 90.9% $$ $$ Similarly \ for \ B, \ E = \left[ \frac { 100{ D }_{ B } }{ { D }_{ B } + { { V }_{ W } }/{ { V }_{ o } } } \right] $$ $$ for \ { V }_{ W } = { V }_{ o }\qquad \qquad \therefore { { V }_{ W } }/{ { V }_{ o } } = 1 $$ $$ \therefore E = \left[ \frac { 100 \times 0.1 }{ 0.1 + 1 } \right] = \left[ \frac { 10 }{ 1.1 } \right] = 9.1% $$ The seperation of A is almost complete from B if the seperation factor B is high. It can be only in the case when \({ D }_{ A }\) is large and \({ D }_{ B }\) is small. For a given value of \({ D }_{ A }\) and \({ D }_{ B }\), the seperation effect can be increased by adjusting the volume ratio given by Nush Densen Equation which says. $$ \boxed { \frac { { V }_{ o } }{ { V }_{ W } } = \frac { 1 }{ { \left( { D }_{ A }{ D }_{ B } \right) }^{ { 1 }/{ 2 } } } } $$

If a solution contains two or more solutes say A and B, it is observed that when A is extracted, some amount of B is also extracted. The extent of the seperation can be expressed in terms of one factor called Seperation Factor \(\beta\) . This is related to the distribution ratio of A and B. $$ \boxed { \beta = \frac { D_{ A } }{ { D }_{ B } } = \frac { { { C }_{ o(A) } }/{ { C }_{ a(A) } } }{ { { C }_{ o(B) } }/{ { C }_{ a(B) } } } } $$ It is ratio therefore no unit and no dimension.

The larger value is always placed in the numerator. \beta must be made as large as possible by choice of extractant and by adjusting the volume ratio.

When \(D_{ A }\) = 10 and \(D_{ B } \)= 0.1. The \(\beta = \frac { 10 }{ 0.1 } = 100%\)

single extraction in case will remove 91% of A and 9% of B. It can be obtained for A, $$ E = \left[ \frac { 100{ D }_{ A } }{ { D }_{ A } + { { V }_{ W } }/{ { V }_{ o } } } \right] $$ for $${ V }_{ W } = { V }_{ o }\qquad \qquad \therefore { { V }_{ W } }/{ { V }_{ o } } = 1 $$ $$ \therefore E = \left[ \frac { 100 \times 10 }{ 10 + 1 } \right] = \left[ \frac { 1000 }{ 11 } \right] = 90.9% $$ $$ Similarly \ for \ B, \ E = \left[ \frac { 100{ D }_{ B } }{ { D }_{ B } + { { V }_{ W } }/{ { V }_{ o } } } \right] $$ $$ for \ { V }_{ W } = { V }_{ o }\qquad \qquad \therefore { { V }_{ W } }/{ { V }_{ o } } = 1 $$ $$ \therefore E = \left[ \frac { 100 \times 0.1 }{ 0.1 + 1 } \right] = \left[ \frac { 10 }{ 1.1 } \right] = 9.1% $$ The seperation of A is almost complete from B if the seperation factor B is high. It can be only in the case when \({ D }_{ A }\) is large and \({ D }_{ B }\) is small. For a given value of \({ D }_{ A }\) and \({ D }_{ B }\), the seperation effect can be increased by adjusting the volume ratio given by Nush Densen Equation which says. $$ \boxed { \frac { { V }_{ o } }{ { V }_{ W } } = \frac { 1 }{ { \left( { D }_{ A }{ D }_{ B } \right) }^{ { 1 }/{ 2 } } } } $$

In choosing a proper solvent for solvent extractions, the following factors must be taken into consideration.

1. The solvent selected should be such that, the solubility of the solute to be extracted is more. This means seperation factor (B) must be large.

2. The two phases used must be totally immiscible.

3. The solvent must not react chemically with the solute present in aqueous solution.

4. The solvent must be recoverable without much expenditure.

5. The density of the solvent must be different than aqueous phase it will help in quick settling of the two phases.

6. The solvent should not be toxic.

7. The solvent should be cheap.

8. The solvent should possess low inflammability.

9. The solvent should have low viscosity, low vapour pressure and low freezing point.

10. The solvent should be readily available.

In choosing a proper solvent for solvent extractions, the following factors must be taken into consideration.

1. The solvent selected should be such that, the solubility of the solute to be extracted is more. This means seperation factor (B) must be large.

2. The two phases used must be totally immiscible.

3. The solvent must not react chemically with the solute present in aqueous solution.

4. The solvent must be recoverable without much expenditure.

5. The density of the solvent must be different than aqueous phase it will help in quick settling of the two phases.

6. The solvent should not be toxic.

7. The solvent should be cheap.

8. The solvent should possess low inflammability.

9. The solvent should have low viscosity, low vapour pressure and low freezing point.

10. The solvent should be readily available.

In general, organic solute (covalent solute) are more soluble in non polar (organic) solvents than water and hydrated salts are more soluble in water (polar) solvent. The inorganic salts in the solution are in the form of ions. In solvent extraction, we must see that solubility of inorganic salts in water should be less and solubility in organic solvent must be increased. The solubility of the metal ions in water is due to the association of water molecules with charged metal ions. in other words due to the hydration. Therefore, if the charged on the metal ions is neutralised, the solubility of the metal ions in the watt will be decreased. The charge on the metal ion is neutralised by reaction of metal ions with the appropriate complexing agent to form the metal-chellate complex. The bulkier the complex and if it is more hydrophobic in nature better will be extraction. .. Each ion will have to be treated differently. Thus, aluminium ions in the solution are usually converted into hydroxy aluminium quinolate by the addition of 8-hydroxy quinolene. The chellate thus formed can be extracted by using benzene or chloroform. It is possible to extract aluminium at pH 5:18, 3 in the presence of iron Nickel and Vanadium. The other complexing agents are dimethyl - glyoxime, acetyl acetone cupferron, \(\alpha\) - nitroso \(\beta\) - naphthol dithizone etc.

In general, organic solute (covalent solute) are more soluble in non polar (organic) solvents than water and hydrated salts are more soluble in water (polar) solvent. The inorganic salts in the solution are in the form of ions. In solvent extraction, we must see that solubility of inorganic salts in water should be less and solubility in organic solvent must be increased. The solubility of the metal ions in water is due to the association of water molecules with charged metal ions. in other words due to the hydration. Therefore, if the charged on the metal ions is neutralised, the solubility of the metal ions in the watt will be decreased. The charge on the metal ion is neutralised by reaction of metal ions with the appropriate complexing agent to form the metal-chellate complex. The bulkier the complex and if it is more hydrophobic in nature better will be extraction. .. Each ion will have to be treated differently. Thus, aluminium ions in the solution are usually converted into hydroxy aluminium quinolate by the addition of 8-hydroxy quinolene. The chellate thus formed can be extracted by using benzene or chloroform. It is possible to extract aluminium at pH 5:18, 3 in the presence of iron Nickel and Vanadium. The other complexing agents are dimethyl - glyoxime, acetyl acetone cupferron, \(\alpha\) - nitroso \(\beta\) - naphthol dithizone etc.

It is the simplest and most widely used method. The method is to be applied when the distribution D is high.

Requirement: Simple glass separating flask beaker, funnel etc.

Experiment: In this technique the aqueous phase containing the solute to be extracted is brought in contact with the immiscible organic solvent in a simple separating funnel. The two phases are shaken vigorously at least for 10-15 minutes. Then are allowed to attain the equilibrium. After the layers become clear, the denser liquid is withdrawn by opening the stop cock of the funnel. Once the denser liquid is separated, then lighter layer is separated.

It is the simplest and most widely used method. The method is to be applied when the distribution D is high.

Requirement: Simple glass separating flask beaker, funnel etc.

Experiment: In this technique the aqueous phase containing the solute to be extracted is brought in contact with the immiscible organic solvent in a simple separating funnel. The two phases are shaken vigorously at least for 10-15 minutes. Then are allowed to attain the equilibrium. After the layers become clear, the denser liquid is withdrawn by opening the stop cock of the funnel. Once the denser liquid is separated, then lighter layer is separated.

When the distribution is small, we have to carry out the multiple extractions. But multiple extraction brings no. of the complications and is very tedious. Kutcher and Steudel devised a continuous extractions to avoid the multiple extractions.

1. When the extracting solvent is heavier than water (aqueous). It is consist of tube and reservoir. The reservoir contain the same organic solvent. The tube is fitted with the condenser. The solvent in reservoir is heated slowly which is converted into vapours, Which move up and are condensed and the organic solvent is converted into liquid which is heavy and descend while moving through aqueous, the solute gets transferred from aqueous to organic and at the bottom we get solution of solute in organic. so the level increases and corresponding solution will fall in reservoir. This continue till maximum amount of solute is transferred from aqueous to organic. Then by opening the stopper at the bottom, we can separate organic and aqueous layer, then solute can be extracted from organic.

2. When organic solvent is lighter than aqueous. In that case reservoir contain organic, which on warming is converted into to the vapours, which ascends and is condensed in condenser which descends through bubbler type of funnel. This liquids goes to bottom but as it is light so it ascends, and passes through solution and here the solute gets transferred from aqueous solution. So the level of of the solution increases and the corresponding gets transferred to reservoir.

When the distribution is small, we have to carry out the multiple extractions. But multiple extraction brings no. of the complications and is very tedious. Kutcher and Steudel devised a continuous extractions to avoid the multiple extractions.

1. When the extracting solvent is heavier than water (aqueous). It is consist of tube and reservoir. The reservoir contain the same organic solvent. The tube is fitted with the condenser. The solvent in reservoir is heated slowly which is converted into vapours, Which move up and are condensed and the organic solvent is converted into liquid which is heavy and descend while moving through aqueous, the solute gets transferred from aqueous to organic and at the bottom we get solution of solute in organic. so the level increases and corresponding solution will fall in reservoir. This continue till maximum amount of solute is transferred from aqueous to organic. Then by opening the stopper at the bottom, we can separate organic and aqueous layer, then solute can be extracted from organic.

2. When organic solvent is lighter than aqueous. In that case reservoir contain organic, which on warming is converted into to the vapours, which ascends and is condensed in condenser which descends through bubbler type of funnel. This liquids goes to bottom but as it is light so it ascends, and passes through solution and here the solute gets transferred from aqueous solution. So the level of of the solution increases and the corresponding gets transferred to reservoir.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

If the sample does not undergo any physical or chemical change. Then there will be no temperature difference between sample and reference. But a temperature difference will definitely occur if sample undergoes any change. For instance in an endothermic change such as melting or dehydration of the sample, the temperature of the sample will be lower than that of reference. On completion of the process the sample will again show zero difference of temperature as compared with reference. On the other hand if an exothermic reaction take place, the sample temperature will be higher than that of reference material.

If we plot a graph of difference of temp. Vs temp. of reference. The graph obtained is in the form of peaks. For endothermic peak will be in the downward and for exothermic the peak is In upward direction. The shape, size of the peaks gives lot, of information about the nature of the test sample. Endothermic curve is for physical change while exothermic is for chemical change. The oxidation reaction give exothermic curve, The melting or fusion are endothermic. Peak areas and peak heights are used for quantitative measurements.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

If the sample does not undergo any physical or chemical change. Then there will be no temperature difference between sample and reference. But a temperature difference will definitely occur if sample undergoes any change. For instance in an endothermic change such as melting or dehydration of the sample, the temperature of the sample will be lower than that of reference. On completion of the process the sample will again show zero difference of temperature as compared with reference. On the other hand if an exothermic reaction take place, the sample temperature will be higher than that of reference material.

If we plot a graph of difference of temp. Vs temp. of reference. The graph obtained is in the form of peaks. For endothermic peak will be in the downward and for exothermic the peak is In upward direction. The shape, size of the peaks gives lot, of information about the nature of the test sample. Endothermic curve is for physical change while exothermic is for chemical change. The oxidation reaction give exothermic curve, The melting or fusion are endothermic. Peak areas and peak heights are used for quantitative measurements.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

Following are the applications of DTA:

1) With the help of DTA, we can find out the effect of heat on Physical and chemical properties of sample.

2) DTA technique is used in fuel analysis, Polymers, ceramics, cements and in pharmaceutical fields.

3) The phenomenon is used to identify the products formed and also their quantitative estimation.

4) DTA gives information regarding transformation, fusion of the sample.

5) It is used for determination of M.P. and hence absolute purity of organic compound,

6) DTA phenomenon is used to find out thermal stability, fusion, phase changes, purity of variety of sample can be determined.

7) Moisture content in the sample can be determined.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

Following are the applications of DTA:

1) With the help of DTA, we can find out the effect of heat on Physical and chemical properties of sample.

2) DTA technique is used in fuel analysis, Polymers, ceramics, cements and in pharmaceutical fields.

3) The phenomenon is used to identify the products formed and also their quantitative estimation.

4) DTA gives information regarding transformation, fusion of the sample.

5) It is used for determination of M.P. and hence absolute purity of organic compound,

6) DTA phenomenon is used to find out thermal stability, fusion, phase changes, purity of variety of sample can be determined.

7) Moisture content in the sample can be determined.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

1) Furnace: It is operating from the temp. of 170-2800°C. The temperature varies 0.1-30°C per minute. The heating is done with heater coils or IR-radiations.

2) Two wells of equal size: One for reference and the other well (cavity) is for sample. The reference is usually Alumina. The reference and sample is placed in the wells.

3) Thermo couple: The temp. of reference and sample and the diff. between two temperature is measured with the help of thermocouples, which is combination of two metals

4) Amplifier: If the diff. of temp. is small, it is difficult to measure accurately then it is to be amplified with amplifier.

5) Atmosphere Control: The heating of sample and reference is done in presence of inert (purge) atmosphere. In other case the ref. or sample may react with the gases of atmosphere.

6) Recorder: Very sensitive recorders are used. It may be photographic light beam galvanometer or electronic potentiometer. A two point recorder records both the diff. temp. and reference material temp as a function of time or temp. ref. on the axis. Recorder will give graph, which on analysis we can have quantitative analysis and from the graph we can decide the change whether it is physical or chemical change.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

1) Furnace: It is operating from the temp. of 170-2800°C. The temperature varies 0.1-30°C per minute. The heating is done with heater coils or IR-radiations.

2) Two wells of equal size: One for reference and the other well (cavity) is for sample. The reference is usually Alumina. The reference and sample is placed in the wells.

3) Thermo couple: The temp. of reference and sample and the diff. between two temperature is measured with the help of thermocouples, which is combination of two metals

4) Amplifier: If the diff. of temp. is small, it is difficult to measure accurately then it is to be amplified with amplifier.

5) Atmosphere Control: The heating of sample and reference is done in presence of inert (purge) atmosphere. In other case the ref. or sample may react with the gases of atmosphere.

6) Recorder: Very sensitive recorders are used. It may be photographic light beam galvanometer or electronic potentiometer. A two point recorder records both the diff. temp. and reference material temp as a function of time or temp. ref. on the axis. Recorder will give graph, which on analysis we can have quantitative analysis and from the graph we can decide the change whether it is physical or chemical change.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Following are the applications of TGA:

1) With TGA we can have quantitative analysis. e.g. The thermal curve of 125.70 mg. of a substance contains mixture of \(Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\) (Mol. wt. = 146.12) and thermally stable salt had a loss in the mass of 6.98 mg. At Tonset 140°C. We can find out the % of Ca-oxalate. $$ Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\ \underrightarrow{140C} \ Ca{ C }_{ 2 }{ O }_{ 4 } + { H }_{ 2 }O\uparrow $$ This indicates 146.12 gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) will lose 18 gm of \( { H }_{ 2 }O\).

Therefore x gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) is loosing 6.98 gm of \({ H }_{ 2 }O\) $$ \therefore \ x\quad =\ \frac { 146.12\ \times \ 6.98 }{ 18 } \ =\ 56.7\ gm\ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O $$ That is \(\therefore \ x\ =\ \frac { 56.7\ \times \ 100 }{ 125.7 } \ =\ 45\ \% \ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\)

2) TGA curve gives the information regarding chemical kinetics.

3) As the Tonset is characteristic property so from Tonset, we can have qualitative analysis.

4) With the help of TGA curve, we can find out the energy of activation of the chemical reaction.

5) For any compound, the products formed at various temperatures can be found from TGA curve.

6) The amount of water present in the clay and soil can be determined.

7) Mechanism of polymer can be studied.

8) The correct drying and ignition temperature in gravimetry can be determined.

9) Thermal decomposition of organic, inorganic and polymeric compounds can be studied.

10) We can find out purity and thermal stability of primary and secondary standards can be determined in titrimetry.

Limitations:

1) TGA is applicable to solid compounds only.

2) As thermocouple is kept very close to sample but not in contact with the sample. Therefore exact temp. of the sample cannot be detected.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Following are the applications of TGA:

1) With TGA we can have quantitative analysis. e.g. The thermal curve of 125.70 mg. of a substance contains mixture of \(Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\) (Mol. wt. = 146.12) and thermally stable salt had a loss in the mass of 6.98 mg. At Tonset 140°C. We can find out the % of Ca-oxalate. $$ Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\ \underrightarrow{140C} \ Ca{ C }_{ 2 }{ O }_{ 4 } + { H }_{ 2 }O\uparrow $$ This indicates 146.12 gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) will lose 18 gm of \( { H }_{ 2 }O\).

Therefore x gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) is loosing 6.98 gm of \({ H }_{ 2 }O\) $$ \therefore \ x\quad =\ \frac { 146.12\ \times \ 6.98 }{ 18 } \ =\ 56.7\ gm\ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O $$ That is \(\therefore \ x\ =\ \frac { 56.7\ \times \ 100 }{ 125.7 } \ =\ 45\ \% \ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\)

2) TGA curve gives the information regarding chemical kinetics.

3) As the Tonset is characteristic property so from Tonset, we can have qualitative analysis.

4) With the help of TGA curve, we can find out the energy of activation of the chemical reaction.

5) For any compound, the products formed at various temperatures can be found from TGA curve.

6) The amount of water present in the clay and soil can be determined.

7) Mechanism of polymer can be studied.

8) The correct drying and ignition temperature in gravimetry can be determined.

9) Thermal decomposition of organic, inorganic and polymeric compounds can be studied.

10) We can find out purity and thermal stability of primary and secondary standards can be determined in titrimetry.

Limitations:

1) TGA is applicable to solid compounds only.

2) As thermocouple is kept very close to sample but not in contact with the sample. Therefore exact temp. of the sample cannot be detected.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The following are the factors:

1) Heating Rate: When the substance is heated to the faster rate, the temperature of the sample (decomposition) is higher, it means temperature changes and as thermogram depends on temperature so the thermogram changes.

2) Heat of Reaction: It depends whether the reaction is exothermic or endothermic, it means heat changes so the thermogram changes.

3) Furnace Atmosphere: The nature of the surrounding atmosphere can have the effect on temperature of decomposition. e.g. instead of N₂ if CO₂ is used as surrounding atmosphere, the decomposition of CaCO3 take place at much higher temperature. $$ CaC{ O }_{ 3 }\quad \overset { \Delta }{ \longrightarrow } \quad CaO\quad +\quad C{ O }_{ 2 } $$ As the CO₂ is on R.H.S. so the reverse reaction takes place, so the nature of thermogram changes. It means whenever furnace atmosphere is enrich with one of the product of reaction the decomposition temp. changes and so the nature of thermogram changes

4) Geometry of Crucible: The geometry of crucible can change slope of TGA curve, usually flat shaped crucible is used, because the diffusion of gases evolved is easier.

5) Characteristics of Samples: Characteristic means amount of sample, particle size packing density, thermal conductivity of sample, the mode of preparation of sample and the atmosphere around it.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The following are the factors:

1) Heating Rate: When the substance is heated to the faster rate, the temperature of the sample (decomposition) is higher, it means temperature changes and as thermogram depends on temperature so the thermogram changes.

2) Heat of Reaction: It depends whether the reaction is exothermic or endothermic, it means heat changes so the thermogram changes.

3) Furnace Atmosphere: The nature of the surrounding atmosphere can have the effect on temperature of decomposition. e.g. instead of N₂ if CO₂ is used as surrounding atmosphere, the decomposition of CaCO3 take place at much higher temperature. $$ CaC{ O }_{ 3 }\quad \overset { \Delta }{ \longrightarrow } \quad CaO\quad +\quad C{ O }_{ 2 } $$ As the CO₂ is on R.H.S. so the reverse reaction takes place, so the nature of thermogram changes. It means whenever furnace atmosphere is enrich with one of the product of reaction the decomposition temp. changes and so the nature of thermogram changes

4) Geometry of Crucible: The geometry of crucible can change slope of TGA curve, usually flat shaped crucible is used, because the diffusion of gases evolved is easier.

5) Characteristics of Samples: Characteristic means amount of sample, particle size packing density, thermal conductivity of sample, the mode of preparation of sample and the atmosphere around it.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The instrumentation of TGA is consisting of the following components:

1) Balance: It must be highly sensitive analytical balance. It must be precise and accurate at experimental temp. The commonly used balance is "Cahn" electro balance. It functions as null type device by providing an electrical force to restore the beam to a predetermined position. When mass changes, the beam of the balance changes, a shutter fixed to the beam changes the amount of light reaching a photo tube (EMR), which causes a restoring force to be generated by passing a current through an electromagnet, that serves as the pivot for the balance beam. A permanent magnet above and below the pivot provides the magnetic attraction to the electromagnet. The force require to restore the beam is proportional to the current which is recorded.

2) Furnace or Heating Device: Here the sample is heated by resistance heaters, IR-radiations, Microwave radiations or heating can also be done by passing the hot vapors of liquids or solids. The furnace must be design in such a manner that heat produced is directly given to the sample. The rate of increase of temp must be 0.15 to 2 deg per minute. The heating should be done in such a manner so that the weighing system should not be affected.

3) Sample Holder: The sample holder should be made up of glass, quartz, stainless steel or pt. The size and shape depends on the weight and nature of the sample

4) Temperature measurement and control: The temperature measurement is done by thermo couples. It is placed very Close to the sample. The emf generated by thermocouple, when heated is incident and is applied on the X-axis of Data acquisition and Manipulation (computer).

5) Recorder: The electrical current obtained with EMR null detector is plotted on the Y-axis and emf. of the thermocouple on X-axis in data acquisition manipulation (Computer).

6) Control of Atmosphere: The results in tile thermo gravimetry depends on the atmosphere of sample see that the atmosphere should be inert gas called purge gas which may be Ar OR N₂.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The instrumentation of TGA is consisting of the following components:

1) Balance: It must be highly sensitive analytical balance. It must be precise and accurate at experimental temp. The commonly used balance is "Cahn" electro balance. It functions as null type device by providing an electrical force to restore the beam to a predetermined position. When mass changes, the beam of the balance changes, a shutter fixed to the beam changes the amount of light reaching a photo tube (EMR), which causes a restoring force to be generated by passing a current through an electromagnet, that serves as the pivot for the balance beam. A permanent magnet above and below the pivot provides the magnetic attraction to the electromagnet. The force require to restore the beam is proportional to the current which is recorded.

2) Furnace or Heating Device: Here the sample is heated by resistance heaters, IR-radiations, Microwave radiations or heating can also be done by passing the hot vapors of liquids or solids. The furnace must be design in such a manner that heat produced is directly given to the sample. The rate of increase of temp must be 0.15 to 2 deg per minute. The heating should be done in such a manner so that the weighing system should not be affected.

3) Sample Holder: The sample holder should be made up of glass, quartz, stainless steel or pt. The size and shape depends on the weight and nature of the sample

4) Temperature measurement and control: The temperature measurement is done by thermo couples. It is placed very Close to the sample. The emf generated by thermocouple, when heated is incident and is applied on the X-axis of Data acquisition and Manipulation (computer).

5) Recorder: The electrical current obtained with EMR null detector is plotted on the Y-axis and emf. of the thermocouple on X-axis in data acquisition manipulation (Computer).

6) Control of Atmosphere: The results in tile thermo gravimetry depends on the atmosphere of sample see that the atmosphere should be inert gas called purge gas which may be Ar OR N₂.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Only solid substances can be analyzed by this method.

In TGA following changes are possible: $$ 1)\ Reactants\ (S)\ \overset { \Delta }{ \longrightarrow } \ product\ (S)\ +\ gas $$ $$2)\ Reactants\ (S)\ +\ gas\ \ \overset { \Delta }{ \longrightarrow } \ \ product\ (S) $$

The second type of changes usually we do not perform in the laboratory. The first type of changes involves loss in the mass or weight. This loss may be due to gas which is obtained by decomposition of reactants on heating or this loss may be due to H₂O present with the reactants. This water is essential water. The essential water is water of crystallization or it is water of constituent’s.

e.g. i) The loss due to gas is $$ CaC{ O }_{ 3 }\ \overset { \Delta }{ \longrightarrow } \ CaO\ +\ C{ O }_{ 2 } $$

ii) The loss due to water of crystallization is $$ CuS{ O }_{ 4 }.5{ H }_{ 2 }O\ \overset { \Delta }{ \longrightarrow } \ CuS{ O }_{ 4 }.{ H }_{ 2 }O\ +\ 4{ H }_{ 2 }O $$

iii) The loss of water due to constituent is $$ 2Fe\left( OH \right) _{ 3 }\ \overset { \Delta }{ \longrightarrow } \ { Fe }_{ 2 }{ O }_{ 3 }\left( S \right) \ +\ 3{ H }_{ 2 }O $$

The graph is plotted mass Vs temperature or time. The graph thus obtained is known as Thermogram. Thermogram is characteristic curve for a given compound. In this graph the horizontal portion i.e. plateau indicate regions where there is no change in the weight while curved portion indicates the loss in the mass. The heating temperature varies from Ambient to 1500°C.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Only solid substances can be analyzed by this method.

In TGA following changes are possible: $$ 1)\ Reactants\ (S)\ \overset { \Delta }{ \longrightarrow } \ product\ (S)\ +\ gas $$ $$2)\ Reactants\ (S)\ +\ gas\ \ \overset { \Delta }{ \longrightarrow } \ \ product\ (S) $$

The second type of changes usually we do not perform in the laboratory. The first type of changes involves loss in the mass or weight. This loss may be due to gas which is obtained by decomposition of reactants on heating or this loss may be due to H₂O present with the reactants. This water is essential water. The essential water is water of crystallization or it is water of constituent’s.

e.g. i) The loss due to gas is $$ CaC{ O }_{ 3 }\ \overset { \Delta }{ \longrightarrow } \ CaO\ +\ C{ O }_{ 2 } $$

ii) The loss due to water of crystallization is $$ CuS{ O }_{ 4 }.5{ H }_{ 2 }O\ \overset { \Delta }{ \longrightarrow } \ CuS{ O }_{ 4 }.{ H }_{ 2 }O\ +\ 4{ H }_{ 2 }O $$

iii) The loss of water due to constituent is $$ 2Fe\left( OH \right) _{ 3 }\ \overset { \Delta }{ \longrightarrow } \ { Fe }_{ 2 }{ O }_{ 3 }\left( S \right) \ +\ 3{ H }_{ 2 }O $$

The graph is plotted mass Vs temperature or time. The graph thus obtained is known as Thermogram. Thermogram is characteristic curve for a given compound. In this graph the horizontal portion i.e. plateau indicate regions where there is no change in the weight while curved portion indicates the loss in the mass. The heating temperature varies from Ambient to 1500°C.

i) Quantitative Analysis: Gelatinous or very small size particles are difficult to filter and are so difficult to estimate. Such ppt. can be converted into ideal solution (suspension) and then can be estimated by either Nephelometry or Turbidimetry.

ii) The amount of Sulphur present in the coal, Oil, rubber, plastics and several organic materials can be determined. That material which contains sulphur is heated at very high temp so that sulphur present is oxidized to the corresponding SO₄^-2 . This is then treated with BaCl₂ so that suspension of BaSO₄ is obtained. This suspension is then subjected to Nephelometer or Turbidimeter.

iii) Water which is required in power plant (Nuclear Reactor) and steam generating plant (Boiler) must be free from any of the suspended particles that testing can be done by Nephelometer and Turbidimeter. If no response from the instrument it, means water is free from of the suspended impurities.

iv) Air is continuously monitored for dust and other particulate matter using these two methods.

v) Determination of molecular weight of macromolecules i.e. polymer.  Polymers have the property of scattering of light. The turbidity of the solution is related to molecular weight of the polymer. $$ \tau = Hc{ M }_{ w } $$ Where H = constant, depends on polymer and medium.

vi) Turbidimetric Titrations: In this case, the solution of SO₄^-2 is taken in the cuvette and after each addition of the titrant i.e. BaCl₂ the precipitate formation takes place. This ppt, formation goes on increasing till all the SO₄^-2 ions are precipitated and so the turbidance goes on increasing and is maximum at the Equivalence point, after that, it remains constant.

vii) The phenomenon is used in sewage work.

viii) Used in pharmaceutical industries and petroleum refineries.

ix) Used in pulp and paper manufacturing.

x) The phenomenon is applied in the determination of suspended material in liquid found in nature.

i) Quantitative Analysis: Gelatinous or very small size particles are difficult to filter and are so difficult to estimate. Such ppt. can be converted into ideal solution (suspension) and then can be estimated by either Nephelometry or Turbidimetry.

ii) The amount of Sulphur present in the coal, Oil, rubber, plastics and several organic materials can be determined. That material which contains sulphur is heated at very high temp so that sulphur present is oxidized to the corresponding SO₄^-2 . This is then treated with BaCl₂ so that suspension of BaSO₄ is obtained. This suspension is then subjected to Nephelometer or Turbidimeter.

iii) Water which is required in power plant (Nuclear Reactor) and steam generating plant (Boiler) must be free from any of the suspended particles that testing can be done by Nephelometer and Turbidimeter. If no response from the instrument it, means water is free from of the suspended impurities.

iv) Air is continuously monitored for dust and other particulate matter using these two methods.

v) Determination of molecular weight of macromolecules i.e. polymer.  Polymers have the property of scattering of light. The turbidity of the solution is related to molecular weight of the polymer. $$ \tau = Hc{ M }_{ w } $$ Where H = constant, depends on polymer and medium.

vi) Turbidimetric Titrations: In this case, the solution of SO₄^-2 is taken in the cuvette and after each addition of the titrant i.e. BaCl₂ the precipitate formation takes place. This ppt, formation goes on increasing till all the SO₄^-2 ions are precipitated and so the turbidance goes on increasing and is maximum at the Equivalence point, after that, it remains constant.

vii) The phenomenon is used in sewage work.

viii) Used in pharmaceutical industries and petroleum refineries.

ix) Used in pulp and paper manufacturing.

x) The phenomenon is applied in the determination of suspended material in liquid found in nature.

i) Effect of Concentration on Scattering:

The attenuation of a parallel beam of radiation by scattering is given by $$ { I }_{ t }={ I }_{ 0 }{ e }^{ -Jl } $$ $$ \log { \frac { { I }_{ 0 } }{ { I }_{ t } } } =KlC $$ $$where\quad K= \frac { J }{ 2.303C } $$ Where \({ I }_{ 0 }\) and \({ I }_{ t }\) are the intensity of the beam before and after passing through the length \(l\) of a turbid medium. The quantity \(J\) is called turbidity coefficient. Its value is often found to be linearly related to the concentration of the scattering particles. As a consequence, a relationship similar to Beers Law is,

ii) Effect of Particle size on Scattering:

The fraction of radiations scattered at any angle depends upon the size and shape of particles responsible for scattering. Those factors which influence the particle size at the time of precipitation in gravimetric, also affect both turbidimetry and nephelometry. Thus gravimetric factors such as the concentration of reagents, rate, and order of mixing, temperature, pH and Ionic strength are important Experimental variables. For proper scattering see that particles size must be uniform.

iii) Effect of Wavelength on scattering:

It has been shown experimentally that the turbidity Coefficient varies with wavelength as given by the equation \(J=S{ \lambda }^{ -t }\) Where S is Constant for a given system. The quantity t depends on the particle size and has a value of 4 when scattering particles are smaller than the wavelength of the radiations incident on it. For particles with a dimension similar to wavelength, \( \lambda \) is found to be 2. For purpose of analysis ordinary white light is used, but if the solution is colored then we have to select that wavelength so that absorption by the medium is minimum.

i) Effect of Concentration on Scattering:

The attenuation of a parallel beam of radiation by scattering is given by $$ { I }_{ t }={ I }_{ 0 }{ e }^{ -Jl } $$ $$ \log { \frac { { I }_{ 0 } }{ { I }_{ t } } } =KlC $$ $$where\quad K= \frac { J }{ 2.303C } $$ Where \({ I }_{ 0 }\) and \({ I }_{ t }\) are the intensity of the beam before and after passing through the length \(l\) of a turbid medium. The quantity \(J\) is called turbidity coefficient. Its value is often found to be linearly related to the concentration of the scattering particles. As a consequence, a relationship similar to Beers Law is,

ii) Effect of Particle size on Scattering:

The fraction of radiations scattered at any angle depends upon the size and shape of particles responsible for scattering. Those factors which influence the particle size at the time of precipitation in gravimetric, also affect both turbidimetry and nephelometry. Thus gravimetric factors such as the concentration of reagents, rate, and order of mixing, temperature, pH and Ionic strength are important Experimental variables. For proper scattering see that particles size must be uniform.

iii) Effect of Wavelength on scattering:

It has been shown experimentally that the turbidity Coefficient varies with wavelength as given by the equation \(J=S{ \lambda }^{ -t }\) Where S is Constant for a given system. The quantity t depends on the particle size and has a value of 4 when scattering particles are smaller than the wavelength of the radiations incident on it. For particles with a dimension similar to wavelength, \( \lambda \) is found to be 2. For purpose of analysis ordinary white light is used, but if the solution is colored then we have to select that wavelength so that absorption by the medium is minimum.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis. This phenomenon is known as Turbidimetry. And if we measure the intensity of scattered radiation then also we can have quantitative analysis, This phenomenon is known as Nephelometry.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis. This phenomenon is known as Turbidimetry. And if we measure the intensity of scattered radiation then also we can have quantitative analysis, This phenomenon is known as Nephelometry.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis of sample. That phenomenon is known as Turbidimetry.

But if we know intensity of scattered radiations then we can also have quantitative analysis. This phenomenon is Known as Nephelometry.

The scattered radiation is always observed at the angle of either 45°, 90° or at 135° to the incident light.

Turbidimetry and Nephelometry involve the use of Very dilute Solutions Therefore suspended particles must have negligible solubility. Such particles scatter the light considerably and therefore great care must he taken that samples are free of dust particles. The particles of the disperse phase must be very fine so that they do not settle down rapidly.

When the light is incident on a solution containing suspended particles. The fraction of the light it scattered and the remaining is transmitted. If we know the intensity of transmitted radiations then we can have quantitative analysis of sample. That phenomenon is known as Turbidimetry.

But if we know intensity of scattered radiations then we can also have quantitative analysis. This phenomenon is Known as Nephelometry.

The scattered radiation is always observed at the angle of either 45°, 90° or at 135° to the incident light.

Turbidimetry and Nephelometry involve the use of Very dilute Solutions Therefore suspended particles must have negligible solubility. Such particles scatter the light considerably and therefore great care must he taken that samples are free of dust particles. The particles of the disperse phase must be very fine so that they do not settle down rapidly.