Preparing a colloidal sol of starch

AIM: To prepare a colloidal sol of starch.

THEORY:

Starch forms a lyophilic sol with water which is the dispersion medium. The sol of starch can be prepared by water to about 1000C. The sol is quite stable and is not affected by the presence of an electrolytic impurity.

 PROCEDURE:

Experiment Observation Inference
Take 50 ml of distilled water in a beaker and heat it to about 1000C.  Add a thin paste of starch to water with stirring. A colourless, translucent sol is obtained. Sol of starch has been prepared.

RESULT– Colloidal sol of starch has been prepared.

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Preparing Colloidal Ferric Hydrochloride

AIM: To prepare a colloidal sol of ferric hydroxide.

THEORY:

Ferric hydroxide forms a lyophobic sol with water which is the dispersion medium.  It is prepared by the hydrolysis of ferric chloride with boiling distilled water as per the reaction:

FeCl3 (aq) + 3H2O →   Fe(OH)3  +  3HCl (aq).

The HCl formed during the reaction tries to destabilize the sol and therefore should be removed from the sol by dialysis. A wine red sol of ferric hydroxide is obtained.

PROCEDURE:

Experiment Observation Inference
Take 50 ml of distilled water in a beaker and heat it to about 1000C.  Add the sol of FeClto water with stirring. A wine red sol is obtained Sol of ferric hydroxide has been prepared

RESULT– Colloidal sol of ferric hydroxide has been prepared.

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Chromatography

AIM: To separate the coloured components present in a mixture of red and green ink by ascending paper chromatography and find their Rf values.

THEORY:

In this type of chromatography, a special adsorbent paper (Whatman filter paper) is used. Moisture adsorbed bon this Whatman filter paper acts as the stationary phase and the solvent acts as the mobile phaseThe mixture to be separated is spotted at one end of the paper. This paper is then developed in a particular solvent by placing the paper in a gas jar, taking care that the spot is above the solvent. The solvent rises due to capillary action and the components get separated out as they rise up with the solvent at different rates. The developed paper is called a chromatogram.

Rf (retention factor) values are then calculated, which is the ratio of the distance moved by the component to the distance moved by the solvent front.

Rf = Distance traveled by the component
         Distance traveled by the solvent front

OBSERVATIONS AND CALCULATIONS: (ON THE BLANK PAGE, USING A PENCIL)

Component Distance Travelled by Different Components Distance Travelled by Solvent Rf Value
Red dr= 2cm ds= 4cm 0.5
Green dg= 3.8cm ds = 4cm 0.95
Chromatography Sheet With Readings
Chromatography Sheet With Readings

RESULT: (ON RULED SIDE

The components of the mixture (red and green colour) separate in the form of spots lying between the origin line and solvent front.

Rf(green) = dg/ds = 3.8/4 =0.95

Rf(red) = dr/ds = 2/4= 0.5

Precautions

  • The strip should not touch the walls of the jar.
  • Do not disturb the jar after putting the strip in it.
  • Allow the colours to seperate before pulling the strip out.

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Carbohydrate Test

AIM: To test the presence of carbohydrate in the given food sample.

 PROCEDURE:

S. No. Exepriment Observation Inference
1

CONC H2SOTEST

Food sample + concentrated H2SO4. Heat

Charring occurs with the smell of burnt sugar Carbohydrate present.
OR
2

MOLISCH’S TEST

Food sample + Molisch’sreagent (1% alcoholic solution of α naphthol) + concentrated H2SO4along the sides of the test tube.

 A purple ring is obtained at the junction of the two layers.  Carbohydrate present.
OR
3

BENEDICT’S / FEHLING’S TEST

Food sample + Benedict’s reagent/ Fehling’s reagent (A mixture of equal amounts of Fehling’s A and Fehling’s B). Heat.

 A red ppt. is obtained.  Carbohydrate present.
OR
4

TOLLEN’S TEST

Food sample + Tollen’s reagent (ammonium silver nitrate solution). Heat on the water bath.

 A silver mirror appears on the walls of the test tube.  Carbohydrate present.

EQUATIONS: (ON BLANK SIDE USING A PENCIL)

 1. CHO(CHOH)4CH2OH (Glucose) + 2Cu2+ + 5OH–     →  COOH(CHOH)4CH2OH(Gluconic acid)   + Cu2O + 3H2O  

2.  CHO(CHOH)4CH2OH(Glucose) + 2[Ag(NH3)2]+ + 3OH  →   COOH(CHOH)4CH2OH(Gluconic acid)  + 4NH3   + 2H2O + 2Ag                                                                                         

RESULT: : (ON RULED SIDE )  – The food sample has been tested for carbohydrate.

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Titration (Oxalic Acid)

AIM: –

(a) To prepare 100ml of M/40 solution of oxalic acid.                                                

(b)Using this calculate the molarity and strength of the given KMnO4 solution. 

APPARATUS AND CHEMICALS REQUIRED

Oxalic acid, weighing bottle, weight box, volumetric flask, funnel, distilled water, chemical balance, beakers, conical flask, funnel, burette, pipette, clamp stand, tile, dilute H2SO4, KMnO4 solution.

(a) THEORY

Oxalic acid is a dicarboxylic acid having molar mass 126gmol-1. It is a primary standard and has the molecular formula COOH-COOH.2H2O. Its equivalent mass is 126/2 = 63 as its n factor is 2 as per the following reaction:

COOH-COOH → 2CO2 + 2H+ + 2e.

PROCEDURE:

  1. Weigh a clean dry bottle using a chemical balance.
  2. Add 3.15g more weights to the pan containing the weights for the weighing bottle.
  3. Add oxalic acid in small amounts to the weighing bottle, so that the pans are balanced.
  4. Remove the weighing bottle from the pan.
  5. Using a funnel, transfer the oxalic acid to the volumetric flask.
  6. Add a few drops of distilled water to dissolve the oxalic acid.
  7. Make up the volume to the required level using distilled water.
  8. The standard solution is prepared.

(b) THEORY

  1. The reaction between KMnO4 and oxalic acid is a redox reaction and the titration is therefore called a redox titration.
  2. Oxalic acid is the reducing agent and KMnO4 is the oxidizing agent.
  3. KMnO4 acts as an oxidizing agent in all the mediums; i.e. acidic, basic and neutral medium.
  4. KMnO4 acts as the strongest oxidizing agent in the acidic medium and therefore dil. H2SO4 is added to the conical flask before starting the titration.
  5. The titration between oxalic acid and KMnO4 is a slow reaction, therefore heat the oxalic acid solution to about 600C to increase the rate of the reaction.

 IONIC EQUATIONS INVOLVED:  

Reduction Half:    MnO4 + 8H+ + 5e  →  Mn2+ + 4H2O] X 2

Oxidation Half:     C2O42-  →  2CO2 + 2e ] X 5

Overall Equation:   2MnO4 + 16H+ + 5C2O42- → 2Mn2+ + 10CO2 + H2O

 INDICATOR– KMnO4 acts as a self indicator.

 END POINT– Colourless to light pink (KMnO4 in the burette)

 PROCEDURE

1. Fill the burette with KMnO4 solution.

2. Pipette out 10ml. of oxalic acid solution into the conical flask.

3. Add half a test tube of dil. H2SO4 and heat the solution to about 600C to increase the rate of the reaction.

4. Keep a glazed tile under the burette and place the conical flask on it.

5. Note down the initial reading of the burette.

6. Run down the KMnO4 solution into the conical flask dropwise with shaking.

7. Stop the titration when a permanent pink colour is obtained in the solution.

8. This is the endpoint. Note down the final burette reading.

9. Repeat the experiment until three concordant values are obtained.

 OBSERVATION TABLE: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)

Volume of Oxalic Acid solution taken = 10mL

S.No. Burette  Readings Volume of KMnO4
I

nitial

Final Used (mL)
1 16 26.5 10.5
2 26.5 36.9 10.4
3 36.9 47.4 10.5

Concordant Value = 10.5mL

 CALCULATIONS: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)

Calculation of amount of oxalic acid to be weighed to prepare 100ml M/20 solution:

 Molecular Mass of Oxalic Acid = 126g/mole

1000 cm3 of 1M oxalic acid require 126g oxalic acid.

1000 cmof M/40 oxalic acid require =126/40g = 3.15g

Using formula:

N1M1V1 = N2M2V2

Where N1=5 (for KMnO4), V1= 10.5          , M1 = ?

N2=2 (for oxalic acid), V= 10ml, M2 = 1/40

M1 = [2*(1/40)*10]/[5*10.5] = 1/105M = 0.0095M

Strength = M X Molar Mass = 158 *( 1/105) = 1.504g/L

 RESULT- (ON RULED SIDE)

The Molarity of KMnO4 =   0.0095M

And the strength of KMnO4 =     1.504g/L 

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Titration of Mohr’s Salt

AIM –

(a) To prepare 250ml of M/20 solution of Mohr’s salt.
(b) Using this calculate the molarity and strength of the given KMnO4 solution.

APPARATUS AND CHEMICALS REQUIRED

Mohr’s salt, weighing bottle, weight box, volumetric flask, funnel, distilled water, chemical balance, dilute H2SO4, beakers, conical flask, funnel, burette, pipette, clamp stand, tile, KMnO4 solution.

(a) THEORY

Mohr’s salt having the formula FeSO4.(NH4)2SO4.6H2O has molar mass 392gmol-1. It is a primary standard.

It’s equivalent mass is 392/1 = 392 as its n factor is 1 as per the following reaction:

      Fe2+ →  Fe3+ + e 

PROCEDURE:

    1. Weigh a clean dry bottle using a chemical balance.
    2. Add 4.9g more weights to the pan containing the weights for the weighing bottle.
    3. Add Mohr’s salt in small amounts to the weighing bottle, so that the pans are balanced.
    4. Remove the weighing bottle from the pan.
    5. Using a funnel, transfer the Mohr’s salt to the volumetric flask. 
    6. Add about 5ml. of dilute H2SO4 to the flask followed by distilled water and dissolve the Mohr’s salt.
    7. Make up the volume to the required level using distilled water.
    8. The standard solution is prepared.

(b) THEORY

  1. The reaction between KMnO4 and Mohr’s salt is a redox reaction and the titration is therefore called a redox titration.
  2. Mohr’s salt is the reducing agent and KMnO4 is the oxidizing agent.
  3. KMnO4 acts as an oxidizing agent in all the mediums; i.e. acidic, basic and neutral medium.
  4. KMnO4 acts as the strongest oxidizing agent in the acidic medium and therefore diluted H2SO4 is added to the conical flask before starting the titration.

 IONIC EQUATIONS INVOLVED:  

Reduction Half:    MnO4 + 8H+ + 5e  →  Mn2+ + 4H2O

Oxidation Half:     5Fe2+  →  5Fe3+ + 5e

Overall Equation:   MnO4 + 8H+ + 5Fe2+  → Mn2+ + 5Fe3+ + 4H2O

 INDICATOR– KMnO4 acts as a self-indicator.

 END POINT– Colourless to light pink (KMnO4 in the burette)

 PROCEDURE

1.       Fill the burette with KMnO4 solution.

2.        Pipette out 10ml. of Mohr’s salt solution into the conical flask.

3.       Add half a test tube of diluted H2SO4.

4.       Keep a glazed tile under the burette and place the conical flask on it.

5.       Note down the initial reading of the burette.

6.       Run down the KMnO4 solution into the conical flask drop wise with shaking.

7.       Stop the titration when a permanent pink color is obtained in the solution.

8.       This is the end point. Note down the final burette reading.

9.       Repeat the experiment until three concordant values are obtained.

OBSERVATION TABLE: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)

Volume of Mohr’s salt solution taken =

S. No. Burette Readings Volume of KMNnO4
Initial Final Used (mL)
1 10 18.8 8.8
2 18.8 27.7 8.9
3 27.7 36.5 8.8

Concordant Value = 8.8mL

CALCULATIONS: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL)

Calculation of amount of Mohr’s Salt to be weighed to prepare 100ml M/20 solution:

Molecular Mass of Mohr’s Salt = 392g/mole

1000 cm3 of 1M KMnOrequire 392g Mohr’s Salt.

250 cmof M/40 KMnO4 require =392/40g = 4.9g

 Using formula:

N1M1V1 = N2M2V2

Where N1=5 (for KMnO4), V1=8.8mL, M1 =?

N=1 (for Mohr’s salt), V= 10ml, M2 = 1/20M

M1 = [1*(1/20)*10]/[5*8.8] = 1/88M = 0.01M

Strength = M X Molar Mass = 158 *( 1/88) = 1.79g/L

RESULT- (ON RULED SIDE)

The Molarity of KMnO4 =  0.01M

And the strength of KMnO4 =  1.79g/L

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Salt Analysis – Chemistry Class XII Practicals

A complete Index of all the various kind of salt analysis experiments:-

Append following Result to each experiment:-

Result:- The given salt contains ________ as acidic radical and ________ as basic radical.

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Magnesium (Mg2+)

AIM: – To identify the given inorganic compound for its acidic and basic radical.

APPARATUS:- Chemical Reagent, Test Tube, Test Tube holder, Spatula

PROCEDURE:-

Preliminary Test:-

Experiment Observation Inference
Smelled the salt. No Ammonical smell. Ammonium absent.
Added dilute hydrochloric acid to the original solution. No Effect. Lead(II) may be present.
Added hydrogen disulphide, hydrochloric acid to the original solution. No Effect. Pb(II), Cu(II) , As(III) absent.
Added dilute hydrochloric acid, concentrated nitric acid, and boiled solution. Then cooled it and added solid ammonium hydroxide. No Effect. Al(III) ,Fe(III) absent.
Passed Hydrogen disulphide gas through the above formed solution. No Effect. Zn (II) ,Mn(II), Ni(II), Co(II) absent.
Added ammonium carbonate to above solution. No Effect. Mg (II) may be present.

Confirmatory Test:-

Experiment Observation Inference
Added ammonium chloride, ammonium hydroxide and disodium hydrogen phosphate to the original solution. White precipitate is formed. Mg(II) Confirmed.

Chemical Equations:-

Ionic equation:-

Mg2+  + HPO42-(aq) + NH4+(aq) –> Mg(NH4)PO4(white)  + H+

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Strontium (Sr2+)

AIM: – To identify the given inorganic compound for its acidic and basic radical.

APPARATUS:- Chemical Reagent, Test Tube, Test Tube holder, Spatula

PROCEDURE:-

Preliminary Test:-

Experiment Observation Inference
Smelled the salt. No Ammonical smell. Ammonium absent.
Added dilute hydrochloric acid to the original solution. No Effect. Lead(II) may be present.
Added hydrogen disulphide, hydrochloric acid to the original solution. No Effect. Pb(II),  Cu(II) ,  As(III) absent.
Added dilute hydrochloric acid, concentrated nitric acid, and boiled solution. Then cooled it and added solid ammonium hydroxide. No Effect. Al(III) , Fe(III) absent.
Passed Hydrogen disulphide gas through the above-formed solution. No Effect. Zn (II) , Mn(II),  Ni(II),  Co(II) absent.
Added ammonium carbonate to above solution. White precipitate is formed. Ba(II), Sr(II), Ca(II) may be present.

Confirmatory Test:-

Experiment Observation Inference
Dissolved precipitate in acetic acid and boiled it. Added few drops of ammonium sulphate to above solution and then added ammonium hydroxide. White precipitate is formed. Sr(II) Confirmed.

Chemical Equations:-

Ionic equation:-

Sr2+ + (NH4)2CO3 (aq) –> SrCO3(s)(white) + 2NH4+(aq)

SrCO3(s) + 2CH3COOH (aq)  –> (CH3COO)2Sr + CO2(g) + H2O(l)

Sr2+(aq) + (NH4)2SO4(aq) –> SrSO4(s)(white)  +  2NH4+(aq)

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Barium (Ba2+)

AIM: – To identify the given inorganic compound for its acidic and basic radical.

APPARATUS:- Chemical Reagent, Test Tube, Test Tube holder, Spatula

PROCEDURE:-

Preliminary Test:-

Experiment Observation Inference
Smelled the salt. No Ammonical smell. Ammonium absent.
Added dilute hydrochloric acid to the original solution. No Effect. Lead(II) may be present.
Added hydrogen disulphide, hydrochloric acid to the original solution. No Effect. Pb(II), Cu(II) , As(III) absent.
Added dilute hydrochloric acid, concentrated nitric acid, and boiled solution. Then cooled it and added solid ammonium hydroxide. No Effect. Al(III) ,Fe(III) absent.
Passed Hydrogen disulphide gas through the above formed solution. No Effect. Zn (II) ,Mn(II), Ni(II), Co(II) absent.
Added ammonium carbonate to above solution. White precipitate is formed. Ba(II), Sr(II), Ca(II) may be present.

Confirmatory Test:-

Experiment Observation Inference
Dissolved precipitate in acetic acid and boiled it. Added few drops of potassium chromate to above solution. Yellow precipitate is formed. Ba (II) Confirmed.

Chemical Equations:-

Ionic equation:-

Ba2+ + (NH4)2CO3 (aq) –> BaCO3(s)(white) + 2NH4+(aq)

BaCO3(s) + 2CH3COOH (aq)  –> (CH3COO)2Ba + CO2(g) + H2O(l)

Ba2+(aq) + K2CrO4(aq) –> BaCrO4(s)(yellow)  + 2K+

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