CBSE CHEMISTRY PRACTICAL

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CBSE Chemistry Practical
CBSE Chemistry Practical

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.

Answer:

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.

Answer:

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.

Answer:

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.

Answer:

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

Answer:

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.

3. Wet test for anions.

ExperimentObservationInference
Little amount of the S.E is taken in a test tube. Then few drops of sodium nitroprusside solution is added.Violet colouration formed.S2‑ confirmed
Dilute HCl is added to the S.E till effervescence ceases. Then BaCl2 solution is added.White ppt formed which is soluble in dil. HCl. White ppt formed which is insoluble in dil. HCl.SO32- confirmed   SO42- confirmed
Dilute HNO3 is added to the S.E till effervescence ceases. Then AgNO3 solution is added.White ppt obtained which is soluble in NH4OH solution.Cl confirmed
Dilute HNO3 is added to the S.E till effervescence ceases. Then AgNO3 solution is added.Pale yellow ppt obtained which is soluble in excess NH4OH solution.Br confirmed
Dilute HNO3 is added to the S.E till effervescence ceases. Then AgNO3 solution is added.Yellow ppt obtained which is insoluble in NH4OH solution.I confirmed
Few drops of dlute sulphuric acid is added to the S.E followed by few drops of KI solution and freshly prepared starch solution.The solution turns deep blue.NO2 confirmed
To the S.E dilute sulphuric acid is added till effervescence ceases. Then freshly prepared ferrous sulphate is added. The mixture is cooled under running tap water. Then concentrated sulphuric acid is slowly added along the side of the test tube.A dark brown ring is formed at the junction of the two liquids.NO3 confirmed
To the S.E, few drops of neutral ferric chloride is added.Red colour solution is formed which produce a brown ppt when heated.CH3COO confirmed
To the S.E few drops of dilute acetic acid is added followed by calcium chloride solution.White ppt formed.C2O4­2- confirmed
To the S.E concentrated nitric acid is added and warmed with excess ammonium molybdate solution.Canary yellow ppt formed.PO43‑ confirmed.

4. Preparation of Original solution:

Cold waterHot waterDil HClConc.HClAqua Regia
     

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

5. Group Analysis:

ExperimentObservationInference
Dil. HCl is added to the original solution.White ppt formed.Group I present
Filtered. H2S is passed through the filtrate.Black ppt formed.Group II present.
Filtered. H2S is boiled off. Then few drops of conc. HNO3 is added and reheated. NH4Cl is added followed by NH4OH till ammoniacal.Ppt formed.Group III present.
Filtered. H2S is passed through the filtrate.Ppt formed.Group IV present.
Filtered. The filtrate is heated to 1/3 of its mass. Then NH4Cl, NH4OH and saturated (NH4)2CO3 is added.White ppt formed.Group V present.
Filtered. Saturated Na2HPO4 is added to the filtrate.White crystalline ppt formed.Group VI present. Mg2+ confirmed.

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.

Identification of organic compounds and functional groups based on observations

1. Alcoholic group- glycerol

ExperimentObservation
a) To 3 mL of 1% borax solution taken in a clean test tube, few drops of phenolphthalein solution are added. To this solution, few drops of sample is added and shaken.Pink colour gets discharged.
b) To 1 mL of the sample solution ,4-5 drops of phenol is added followed by 2-3 drops of conc. sulphuric acid. The mixture is heated. Cooled. Diluted with water and finally ammonium hydroxide solution is added.A red coloured solution is produced
c) To 1 mL of the sample solution, 1 mL of copper sulphate solution is added and then 1 mL of sodium hydroxide solution is added.A blue coloured solution is produced.

2. Aldehyde group- formaldehyde

ExperimentObservation
a) To 2 mL of the sample few crystals of resorcinol is added and shaken. Then 1 mL of conc. sulphuric acid is along the side of the test tube.A red ring is formed at the junction of the two liquids while a white ppt forms in aqueous layer.
b) To 2 mL of the sample , 1 mL of freshly prepared pyrogallol solution is added. The content is shaken. 2 mL of conc. HCl is added and then the content is warmed in a water bath.A white ppt is formed which readily turns pink and then deep red.
c) To 2 mL of the sample, 1 mL of tollen’s reagent is added and warmed in hot water bath.A shiny silver mirror is formed.

3. Ketonic group- acetone

ExperimentObservation
a) Few crystals of iodine are taken and then 2 mL of the sample is added. The mixture is shaken to dissolve iodine. Few drops of NaOH solution is added and warmed.Yellow ppt formed.
b) To 2 mL of the sample solution, 0.5 mL of NaOH solution is added followed by 2-3 drops of sodium nitroprusside solution. Allowed to stand for some time and then warmed gently.A ruby red colouration formed which fades to yellow or disappears.
c) To about 0.5 mL of mercuric chloride solution, NaOH solution is added till no further change occurs. To it sample solution is added.Yellow crystals formed dissolves on adding the sample solution.

4.Carboxylic acid- benzoic acid

ExperimentObservation
a) The sample solution is treated with moist blue litmus solution.The solution turns red.
b) To 2 mL of the sample solution, 2 mL of sodium bicarbonate solution is added.Effervescence seen.
c) To 2 mL of the sample solution, 2 mL of ethanol is added and few drops of conc. H2SO4 are added. The mixture is warmed.A pleasant fruity smell is obtained.

5. Amino group-aniline

ExperimentObservation
a) To 1 mL of the sample solution, 1 mL of conc. HCl is added. Now, few drops of neutral ferric chloride solution is added and then diluted with water.Pale green colouration.
b) To 1 mL of the sample solution 2-3 drops of sodium hypochlorite solution is added and shaken.Violet or purple colouration is obtained.
c) To 1 mL of the sample solution few drops of dilute sulphuric acid is added followed by 1 mL of potassium dichromate solution. The mixture is shaken and warmed.A deep red colouration is produced which finally changes to deep blue or black.

6. Unsaturation

ExperimentObservation
a) 0.2 mL of the sample is dissolved in water or acetone. Then 1% alkaline KMnO4 solution is added to it.The purple colour disappears.
b) 0.2 mL of the sample is dissolved in water or acetone. Then Br2/H2O or Br2/CCl4 solution is added to it. A glass rod dipped in NH4OH is held at the mouth of the test tube.Reddish-brown colour of Br2 disappears, but white fumes are not formed around the glass rod.

7. Phenolic-OH

ExperimentObservation
a) 0.2 mL of the sample is dissolved in 2 mL of alcohol. Then 1-2 drops of neutral FeCl3 solution is added to it.The solution turns violet or blue or green.
b) 1-2 drops of aniline is dissolved in dilute HCl.The solution is cooled and diazotised with cld NaNO2 solution. Few drops of this diazotised solution is added to the alkaline solution of the sample.Red coloured azo dye formed.

Characteristic Tests of carbohydrates and proteins

1. Carbohydrate-glucose

ExperimentObservation
a) To 2 mL of the sample solution, 1 mL of Fehling’s solution is added and warmed.A brick red ppt is obtained.
b) To 2 mL of the sample solution, 2-3 drops of α-naphthol solution is added. After that, conc. sulphuric acid is slowly added along the side of the test tube.A violet ring is formed at the junction of the two liquids.
c) To 1 mL of the sample solution, 1mL of lead acetate solution is added followed by ammonium hydroxide solution. The content is boiled.A white ppt is formed which turns to salmon pink on boiling with ammonium hydroxide.

2. Protein- powdered milk

ExperimentObservation
a) The sample is dissolved in water. 2 mL of such solution is treated with 1 mL of copper sulphate solution and shaken. Now 3 mL of NaOH solution is added.Violet colouration is developed.
b) The sample is dissolved in water. 2 mL of such solution is treated with 1 mL of nitric acid. The content is boiled. The 5 mL of ammonium hydroxide solution is added.Orange colour is produced.

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:

Serial NoColour of componentsDistance of components from the point of application (cm)Final distance of the solvent from the point of application (cm)Rf value
1 axa/x
2 bxb/x
3 cxc/x

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:

Serial NoColour of componentsDistance of components from the point of application (cm)Final distance of the solvent from the point of application (cm)Rf value
1 axa/x
2 bxb/x
3 cxc/x