Class 12 Record Experiment 2

 (WRITE IN RHS)                     Experiment 2                                                        

Estimation of unknown KMnO4 using M/20 oxalic acid solution

AIM:-

1. To find the mass of oxalic acid to prepare 250ml of  (M/20) solution.

2. To find the molarity of unknown KMnO4 solution using M/20 oxalic acid solution.

3. To estimate the strength (amount as grams in 1 litre) of KMnO4  solution.

THEORY:-

Oxalic acid a primary standard is chemically H2C2O4.2H2O (molar mass = 126g/mol)

To prepare M/20 solution of oxalic acid, the weight of oxalic acid required can be calculated by using the formula

Molarity  =    (WbX1000) / (Mb X 250)    

          Wb    = (MOLARITY X Mb) / 4   

                  =  (0.05 X 126) / 4      =  1.575  g

Here 

Mb = Molecular mass of oxalic acid                = 126g/mol

Wb = Weight of oxalic acid  required             =1.575g

Oxidising agent : unknown potassium permanganate solution

Reducing agent : standard M/20 oxalic acid

KMnO4 (molar mass = 158g/mol) is an oxidising agent and it oxidises carbon present in oxalic acid from +3 to +4 oxidation state. The manganese of KMnO4 is reduced from +7 to +2 oxidation state.

PROCEDURE:- 

 1) Preparation of 250ML standard solution of M/20 oxalic acid

1.575 g of oxalic acid is weighed into a 250ml standard flask, made up to the mark using distilled water and labelled as M/20 .

2) Titration and estimation of unknown KMnO4 with standard M/20 oxalic acid solution (learn well all the steps of procedure for exam) 

1. Take 50ml burette and wash it with distilled water and then rinse it with few ml of given KMnO4 solution and place it in the burette stand after filling with unknown KMnO4 with the help of a funnel.

(Write in LHS) OBSERVATIONS AND CALCULATIONS:-    

AIM 1:-    

Weight of watch glass                                                                    = 10g

Weight of watch glass + oxalic acid                                             = 11.575g

Weight of oxalic acid dissolved in 250ml of distilled water  = 1.575g

Molarity of oxalic acid solution prepared = (1.575 × 4)/126  =M/20

AIM 2 and 3 :-

Volume of oxalic acid  solution           (V1)                                     = 20ml

Molarity of oxalic acid solution         (M1)                                     =(M/20)

Standard oxalic acid solution (M/20) against unknown KMnO4 solution

SL.NO.	VOLUME OF M/20 OXALIC ACID  SOLUTION	INITIAL  READING OF BURETTE	FINAL READING  OF BURETTE	VOLUME OF  KMnO4 USED
1.	..........ml	..........ml	..........ml	..........ml
2.	..........ml	..........ml	..........ml	..........ml
3.	..........ml	..........ml	..........ml	..........ml

PRINCIPLE OF VOLUMETRIC ANALYSIS 

(M1V1) / n1 = (M2V2) / n2

From ionic equations:- 

n1  = stoichiometric coefficient of reactant 1 oxalic acid                           =5

n2  = stoichiometric coefficient of reactant 2 Potassium permanganate =2

Volume of potassium permanganate solution   = (V2) = ...........ml

Therefore Molarity of KMnO4  solution              = (M2) = (M1V1n2)/(n1V2)

                                                                                     = ……………………….M

Molecular mass of potassium permanganate     = 158g/mol

Strength of potassium permanganate  (M2)         = ...............M × 158g/mol=................g/ l

RESULT:-

1. Mass of oxalic acid used to prepare M/20 , 250ml solution = .........g

2.Molarity of the given KMnO4 solution = ............M

3. Strength of given KMnO4 solution = ............g/l

(Write in RHS)

2. Take a pipette and wash it with distilled water and then rinse it with few ml of given standard (M/20) oxalic acid solution. Pipette out 20ml into a clean 250ml conical flask. 

3. Add 20ml (Approximately one test tube full) of dilute sulphuric acid into the conical flask to make the solution acidic. Heat the contents of the conical flask to about 70 to 800C.

4. Place the conical flask along with its content below the nozzle of the burette and start adding KMnO4 solution from the burette drop wise into the conical flask with continuous swirling until a permanent pink colour just appear in the solution of conical flask.

5. Note down the reading of the upper meniscus of the KMnO4 solution in the burette and repeat the experiment to get three concordant values (close values)

BURETTE SOLUTION	Unknown POTASSIUM PERMANGANATE  SOLUTION
PIPETTE SOLUTION	Standard M/20  OXALIC ACID SOLUTION
(SELF) INDICATOR	POTASSIUM PERMANGANATE
ENDPOINT	COLOURLESS TO PERMANENT  LIGHT PINK

RESULT:-

1. Mass of oxalic acid used to prepare M/20 , 250ml solution = .........g

2.Molarity of the given KMnO4 solution = ............M

3. Strength of given KMnO4 solution = ............g/l

PRCAUTIONS:-

1. Always add one test tube full of 4N sulphuric acid to 20ml of oxalic acid solution before titration

2. Always add KMnO4 solution drop wise otherwise the solution will become brown due to MnO2 form.

3. Always add dilute sulphuric acid into oxalic acid solution while preparing.

4. Always take the reading of KMnO4 solution in the burette from the upper meniscus.

5. Always use distilled water for preparing the solution.