## 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.

## Study of the rate of reaction

This experiment is designed to find the effect of concentration of the reactants on the rate of a chemical reaction.

You are provided with two solutions:

(a) C-13 is a solution of sodium thiosulphate crystals of strength 0.2 M

(b) C-14 is a solution of HCl of strength 0.1 M.

Procedure:

Take 5 beakers labelled 1 to 5. With the help of a measuring cylinder, put sodium thiosulphate solution and distilled water according to the table given below:

Place beaker number 1 over a piece of paper with a cross mark (X) on it.

Now add 10 mL of the solution C-14(HCl) to this solution and start the stop-watch at the same time. Swirl the contents of the beaker and return it over the over mark.

Look down vertically on the cross mark and stop the stop-watch as soon as tge cross on the paper become invisible. Note the time in the stop-watch.

Na2S2O3 (aq) + 2HCl(aq) → 2NaCl (aq) + SO2(g) + H2O + S(Colloidal)

Repeat the experiment by adding 10 mL of C-14 to the beaker labelled 2,3,4 and 5 and note the time taken in each case for the cross mark on the paper to become invisible.