## Volumetric Analysis:Oxidation-Reduction Titration

### A. Potassium manganate(VII) / ammonium iron (II) sulphate

#### 1. Determination of water of crystallization of ammonium iron (II) sulphate.

You are provided with two solutions as follows:

C-10 is a solution containing 1.95 gms of potassium manganate(VII), KMnO4 per litre.

C-11 is a solution prepared by dissolving 23.2 gms of hydrated ammonium iron (II) sulphate crystals, (NH4)2SO4.FeSO4.xH2O per litre.

Procedure:

Rinse and fill the burette with the given solution C-10 (KMnO4). Pipette out 20 mL or 25 mL of C-11 (hydrated ammonium iron (II) sulphate solution) and transfer into a clean conical flask. To this add 20 mL of C-12 (dilute sulphuric acid) specially provided for titration.Titrate the solution in the conical flask with C-10 (KMnO4) slowly, till one drop of this gives a light permanent pink colour to the solution C-11 in the flask. The pink colour should not disappear on shaking the contents in the conical flask.Repeat the above procedure to get at least two concordant readings.Tabulate your readings.

State:

(a) The capacity of the pipette used.

(b) The titre value you intend to use in your calculations.

The equations for the above reactions are as follows:

2KMnO4 + 8H2SO4 + 10 (NH4)2SO4.FeSO4.xH2O → K2SO4 + 2MnSO4 +10(NH4)2SO4 + 5Fe2(SO4)3 + 8H2O + 10 x H2O

The ionic equation for the reaction is:

2MnO4 + 10Fe2+ + 16H+ → 2Mn2+ + 10Fe3+ + 8H2O

[K=39, Fe= 56, Mn= 55, S=32, N=14, H=1, O=16]

Calculate the following:

1. The molarity of the solution of Potassium manganate(VII) C-10.
2. The molarity of hydrated ammonium iron(II) sulphate solution C-11.
3. The molecular mass of hydrated ammonium iron(II) sulphate deduced from the experimental data.
4. The numerical value of x in (NH4)2SO4.FeSO4.xH2O.

#### 2. Determination of percentage purity of ammonium iron (II) sulphate in the impure sample

You are provided with two solutions as follows:

C-10 is a solution containing 1.95 gms of potassium manganate(VII), KMnO4 per litre.

C-11 is a solution prepared by dissolving 23.2 gms of impure sample of hydrated ammonium iron (II) sulphate per litre.

Procedure:

Rinse and fill the burette with the given solution C-10 (KMnO4). Pipette out 20 mL or 25 mL of C-11 (hydrated ammonium iron (II) sulphate solution) and transfer into a clean conical flask. To this add 20 mL of C-12 (dilute sulphuric acid) specially provided for titration.Titrate the solution in the conical flask with C-10 (KMnO4) slowly, till one drop of this gives a light permanent pink colour to the solution C-11 in the flask. The pink colour should not disappear on shaking the contents in the conical flask.Repeat the above procedure to get at least two concordant readings.Tabulate your readings.

State:

(a) The capacity of the pipette used.

(b) The titre value you intend to use in your calculations.

The equations for the above reactions are as follows:

2KMnO4 + 8H2SO4 + 10 (NH4)2SO4.FeSO4.xH2O → K2SO4 + 2MnSO4 +10(NH4)2SO4 + 5Fe2(SO4)3 + 8H2O + 10 x H2O

The ionic equation for the reaction is:

2MnO4 + 10Fe2+ + 16H+ → 2Mn2+ + 10Fe3+ + 8H2O

[K=39, Fe= 56, Mn= 55, S=32, N=14, H=1, O=16]

Calculate the following:

1. The molarity of the solution of Potassium manganate(VII) C-10.
2. The molarity of hydrated ammonium iron (II) sulphate solution C-11.
3. The concentration of hydrated ammonium iron (II) sulphate in gm/litre.
4. The percentage purity of hydrated ammonium iron (II) sulphate in the impure sample.

#### 3.Determination of percentage purity of impure sample of potassium manganate (VII) in the impure sample.

You are provided with two solutions as follows:

C-10 is a solution containing 1.96 gms of potassium manganate (VII), KMnO4 per litre.

C-11 is a solution prepared by dissolving 23.2 gms of impure sample of hydrated ammonium iron (II) sulphate per litre.

Procedure:

Rinse and fill the burette with the given solution C-10 (KMnO4). Pipette out 20 mL or 25 mL of C-11 (hydrated ammonium iron (II) sulphate solution) and transfer into a clean conical flask. To this add 20 mL of C-12 (dilute sulphuric acid) specially provided for titration.Titrate the solution in the conical flask with C-10 (KMnO4) slowly, till one drop of this gives a light permanent pink colour to the solution C-11 in the flask. The pink colour should not disappear on shaking the contents in the conical flask.Repeat the above procedure to get at least two concordant readings.Tabulate your readings.

State:

(a) The capacity of the pipette used.

(b) The titre value you intend to use in your calculations.

The equations for the above reactions are as follows:

2KMnO4 + 8H2SO4 + 10 (NH4)2SO4.FeSO4.xH2O → K2SO4 + 2MnSO4 +10(NH4)2SO4 + 5Fe2(SO4)3 + 8H2O + 10 x H2O

The ionic equation for the reaction is:

2MnO4 + 10Fe2+ + 16H+ → 2Mn2+ + 10Fe3+ + 8H2O

[K=39, Fe= 56, Mn= 55, S=32, N=14, H=1, O=16]

Calculate the following:

1. The molarity of the solution of hydrated ammonium iron (II) sulphate C-11.
2. The molarity of potassium manganate (VII) solution C-10.
3. The concentration of potassium manganate (VII) solution C-10.
4. The percentage purity of potassium manganate (VII) in the impure sample.

### B. Potassium manganate(VII) / oxalic acid

#### 1. Determination of the percentage purity of sample of oxalic acid solution.

You are provided with two solutions as follows:

C-10 is a solution containing 2.8 gms of potassium manganate (VII), KMnO4 per litre.

C-11 is a solution prepared by dissolving 6.25 gms of impure sample of oxalic acid crystals (H2C2O4.2H2O) per litre.

Procedure:

Rinse and fill the burette with potassium manganate (VII) solution C-10 (KMnO4). Pipette out 20 mL or 25 mL of the oxalic acid solution C-11 (H2C2O4.2H2O) in a clean conical flask. To this, add 20 mL of dilute sulphuric acid (H2SO4) C-12, specially provided for this purpose. Warm the contents of the flask to 60oC -70oC. The heating should be continued till the first bubble appears at the bottom of the flask. Remove the conical flask from fire and titrate this solution by running solution C-10 from the burette. Shake the solution constantly till a permanent pale pink colour is obtained. Ensure that the pink colour obtained does not disappear on shaking the contents of the conical flask. Repeat the above procedure to get at least two concordant readings. Tabulate your readings.

State:

(a) The capacity of the pipette used.

(b) The titre value you intend to use in your calculations.

The equations for the above reactions are as follows:

2KMnO4 + 4H2SO4 + 5H2C2O4 → K2SO4 + 2MnSO4 + 8H2O + 10CO2

2MnO4 + 5C2O42- + 16 H+ → 2Mn2+ + 10CO2 + 8H2O

[K=39, Mn=55, C=12, O=12, H=1]

Calculate the following:

1. The molarity of potassium manganate (VII) solution C-10.
2. The molarity of oxalic acid solution C-11.
3. The strength of oxalic acid solution in gms per litre.
4. The percentage purity of the sample of oxalic acid solution.

#### 2.Determination of water of crystallization of oxalic acid.

You are provided with two solutions as follows:

C-10 is a solution containing 2.8 gms of potassium manganate (VII), KMnO4 per litre.

C-11 is a solution prepared by dissolving 5.83 gms of impure sample of oxalic acid crystals (H2C2O4.2H2O) per litre.

Procedure:

Rinse and fill the burette with potassium manganate (VII) solution C-10 (KMnO4). Pipette out 20 mL or 25 mL of the oxalic acid solution C-11 (H2C2O4.2H2O) in a clean conical flask. To this, add 20 mL of dilute sulphuric acid (H2SO4) C-12, specially provided for this purpose. Warm the contents of the flask to 60oC -70oC. The heating should be continued till the first bubble appears at the bottom of the flask. Remove the conical flask from fire and titrate this solution by running solution C-10 from the burette. Shake the solution constantly till a permanent pale pink colour is obtained. Ensure that the pink colour obtained does not disappear on shaking the contents of the conical flask. Repeat the above procedure to get at least two concordant readings. Tabulate your readings.

State:

(a) The capacity of the pipette used.

(b) The titre value you intend to use in your calculations.

The equations for the above reactions are as follows:

2KMnO4 + 4H2SO4 + 5H2C2O4 → K2SO4 + 2MnSO4 + 8H2O + 10CO2

2MnO4 + 5C2O42- + 16 H+ → 2Mn2+ + 10CO2 + 8H2O

[K=39, Mn=55, C=12, O=12, H=1]

Calculate the following:

1. The molarity of the solution of Potassium manganate (VII) C-10.
2. The molarity of hydrated ammonium oxalic acid solution C-11.
3. The molecular mass of hydrated oxalic acid deduced from the experimental data.
4. The numerical value of x in H2C2O4.xH2O

## Qualitative Analysis

### 1. Dry Test for anions:

a) Dilute sulphuric acid is added to dry solid sample.

b) Concentrated sulphuric acid is added to dry solid sample and heated.

### 2. Preparation of sodium carbonate extract:

Dry sample and anhydrous sodium carbonate is taken in 1:3 ratio in a beaker and boiled with 20 mL of water for 10 to 15 mins. Filtered hot and with the filtrate(sodium carbonate extract S.E) the following test are done.

### 4. Preparation of Original solution:

The sample given is soluble in ______ to produce the original solution.

### 6. Confirmatory test for cations:

i) The residue of group I is dissolved in hot water and potassium chromate solution is added. Heavy yellow ppt is formed. Pb2+ confirmed.

ii) The residue of group II is dissolved in conc. HNO3 and then divided into two portions.

a) First portion is treated with potassium chromate solution. Heavy yellow ppt is formed. Pb2+ confirmed.

b) Second portion is treated with potassium ferrocyanide solution. Chocolate brown ppt formed. Cu2+ confirmed.

iii) The residue of group III is dissolved in conc. HCl and divided into two portions.

a) First portion is treated with sodium hydroxide solution. White gelatinous ppt obtained. Al3+ confirmed.

b) Second portion is treated with potassium ferrocyanide solution. Prussian blue colouration formed. Fe3+ confirmed.

iv) The residue of group IV is treated with minimum quantity of dil. HCl and heated for a long time to boil off H2S. Filtered.

Residue is dissolved in aqua regia or (NaOCl + HCl) and divided into two parts.

a) First portion is treated with amyl alcohol and shaken with NH4SCN. Amyl alcohol layer turns blue. Co2+ confirmed.

b) In the second portion NH4Cl is added followed by NH4OH till alkaline. Then excess of dimethyl glyoxime is added. Red ppt obtained. Ni2+ confirmed.

Filtrate is divided into two parts.

a) First part is treated with NaOH solution. The ppt formed is dissolved in conc. HNO3 in presence of PbO2. Purple colouration formed. Mn2+ confirmed.

b) In the second part potassium ferrocyanide solution is added. Bluish white ppt formed. Zn2+ confirmed.

v)The residue of group V is dissolved in dil.acetic acid and divided into three parts.

a) First part is treated with potassium chromate solution. Yellow ppt formed. Ba2+ confirmed.

b) If Ba2+ is absent in the first part, to the second portion ammonium sulphate solution is added. White ppt formed. Sr2+ confirmed.

c) If both Ba2+ and Sr2+ are absent, ammonium oxalate solutions is added to the third portion. White ppt formed. Ca2+ confirmed.

### 7. Detection of group zero:

Dry sample is NaOH solution is added and heated. Pungent smelling gas produced which produce dense white fumes when come in contact with a glass rod dipped in conc. HCl. Group Zero present.

The gas produced is passed through nessler’s reagent. The Nessler’s reagent turns brown. NH4+ confirmed.

## Preparation of inorganic compounds

### 1. Preparation of ferrous ammonium sulphate

Principle: Ferrous ammonium sulphate is prepared by crystallisation from saturated aqueous solution of equimolar quantity of ferrous sulphate and ammonium sulphate containing small amount of sulphuric acid.

FeSO4.7H2O + (NH4)2SO4 → (NH4)2SO4.FeSO4.6H2O + H2O

Procedure: 7g of ferrous sulphate and 3.5 g of ammonium sulphate are taken in a beaker. To it, 2-3 mL of sulphuric acid is added. 25 mL of boiled distilled water is added to the mixture in small amount with constant stirring. The solution is then boiled until it reaches the crystallisation point. The solution is covered with a lid and cooled gently when greenish crystals  of Mohr’s salt are formed. The mother liquor is decanted out and the adhering acid solutions on the crystals are washed with a small amount of ethanol. The crystals are dried.

### 2. Preparation of Potash Alum:

Principle: Ferrous ammonium sulphate is prepared by crystallisation from saturated aqueous solution of equimolar quantity of potassium sulphate and aluminium sulphate containing small amount of sulphuric acid.

K2SO4 + Al2(SO4)3.18H2O + 6H2O → K2SO4.Al2(SO4)3.24H2O

Procedure: 10 g of aluminium sulphate and 3 g potassium sulphate are separately mixed in 20 mL water followed with 5 mL of sulphuric acid(in aluminium sulphate). The solutions are mixed in a porcelain basin and heated to crystallisation point. The solution is covered with a lid and cooled gently when white crystals of potash alum are formed. The mother liquor is decanted out and the adhering acid solutions on the crystals are washed with a small amount of ethanol. The crystals are dried.

### 3. Preparation of Potassium Ferric Oxalate:

Principle: Potassium Ferric Oxalate or potassium trioxalatoferrate(III) is prepared by dissolving freshly prepared ferric hydroxide in potassium oxalate and oxalic acid solution.

FeCl3 + 3KOH → Fe(OH)3↓ + 3KCl

2Fe(OH)3 + 3(COOH)2.2H2O → Fe2(C2O4)3 + 12H2O

Fe2(C2O4)3 + 3(COOK)2.H2O → 2K3[Fe(C2O4)3].3H2O

Procedure: 5g FeCl3, 5.5g KOH and 6g oxalic acid are dissolved in 25mL of water separately. The KOH solution is added to FeCl3 solution in small portions. The ppt of ferric hydroxide is filtered and washed with hot water. In the oxalic acid solution, 2g of KOH beads is added and dissolved by constant stirring. To this alkaline oxalic acid solution, ferric hydroxide ppt is added in small portions and dissolved by stirring. The solution thus obtained is filtered in a porcelain basin and heated to crystallisation point. The solution is covered with a black paper and cooled gently when bright green crystals of Potassium Ferric Oxalate are formed.

## Content based experiment

### 1. Separation of pigments from extracts of leaves and flowers by paper chromatography and determination of Rf values.

Principle: Extracts of leaves and flowers contains chlorophyll, xanthophylls , carotene etc. The spot of the extract is applied on one end of the strip of filter paper and dipped into a suitable solvent. The components of the extract rise up at different rates and separated from one another.

Procedure: Small pieces of spinach are put in a mortar with 7 to 8 mL of methanol. The mixture is grinded to paste by a pestle. A line is drawn with a pencil 3 cm above the lower end of a strip of filter paper. With the help of a capillary tube, a spot of the extract is put on the middle of the line. The spot is dried. Same process is carried out over the same spot to get a extract rich spot.

A mixture of 95 mL petroleum ether and 5 mL acetone is prepared. The filter paper containing the spot is suspended vertically from a hook into the solvent, keeping the spot 2cm above the solvent level. The solvent rises along the components of the extract. As the solvent rises 15 cm, the chromatogram is taken out, and the spots of different components are marked with a pencil. The strip is dried. The distance travelled by the solvent from the point of application of the spot and that of the components is noted. Rf value calculated.

Observation:

### 2. Separation of constituents present in an inorganic mixture by paper chromatography and determination of Rf values.

Principle: The spot of the mixture of cations is applied on one end of the strip of filter paper and dipped into a suitable solvent. The components of the extract rise up at different rates and separated from one another.

Procedure: A line is drawn with a pencil 3 cm above the lower end of a strip of filter paper. With the help of a capillary tube, a spot of the solution of mixture of Cu2+ and Co2+ is put on the middle of the line. The spot is dried. Same process is carried out over the same spot to get a extract rich spot.

A mixture of solvent is formed by mixing acetone, ethyl acetate and 6(M) HCl in 9:9:2 ratio. The filter paper containing the spot is suspended vertically from a hook into the solvent, keeping the spot 2cm above the solvent level. The solvent rises along the components of the extract. As the solvent rises 15 cm, the chromatogram is taken out, and the spots of different components are marked with a pencil. The strip is dried and kept in a jar containing ammonia vapour for 15 mins to neutralise the acid. The strip is taken out, sprayed with spray reagent, dried. Co2+ produces a yellowish-orange spot and Cu2+ produces an olive green spot. These spots are encircled. The distance travelled by the solvent from the point of application of the spot and that of the components is noted. Rf value calculated.

Observation: