Sodium Hydroxide

Determination of strength of 0.1(N) Sodium hydroxide (NaOH) by standard Oxalic acid .

PRINCIPLE :

               Standardization of strong  base by oxalic acid can be consider as neutralization reaction between strong base and week acid . Phenolphthalein Should be used as indicator . The following reaction takes place

                               H⁺      +       OH ^-     –––––>       H₂O

                             acid             base                    water

The calculation is performed by using the following equation :-

                     

                              V₁S₁ = V₂S₂       where,    S₁ = Strength of base solution

                                                                       V₁ = Volume of base solution

                                                                       S₂ = Strength of acid solution

                                                                       V₂ = Volume of acid solution

CHEMICALS :

                 a)  0.1 (N)  NaOH  (Secondary standard solution)

              b)  0.1 (N)  Oxalic acid   (Primary standard solution)

              c)  Indicator  -  Phenolphthalein .

             

APPARATUS :

a)     Conical flask

b)    Pipette

c)     Burette

d)    Funnel

e)     Volumetric flask

f)      Beaker

g)     Measuring cylinder

h)     Stand clamp .

                                                                                                                 

PROCEDURE :-

                    1)  Filling the burette : A clear and dried burette is filled  with 0.1 (N) basic solution and lower meniscus of the solution  is adjusted to zero.

                 2)  Placement of  0.1(N) standard oxalic acid solution is conical flask by pipette. A  clear and dried 10ml pipette is used to take 0.1(N) oxalic acid solution from the volumetric flask . Add 10ml of distilld water and 3-4 drops Phenolphthalein solution to it. This solution remains colorless.

                3) Titration :

                                a) The  bottom of  the  conical  flask is  wiped and a piece of white paper is placed below it .

                                b) Take initial burette reading.

                                c) Add  drop by  drop  NaOH solution form the burette to the conical flask along with gently shaking.  Each drop produces a pink color which disappears rapidly .

                                d) At the point the color of the solution becomes pink which remain for long time .

                                c) Take the final burette reading and fill the table, from which we can calculate the strength of solution .

                                                 Table for 0.1(N) NaOH :-

Solution No.	Volume of acid	Initial burette reading	F.B.R	Difference	Mean
2	10
2	10
2	10

            

                       Where, 

                                  V₁ = Volume of base            =                              ml

                                   S₁ = Strength of base ( ? )    =                             (N)

                                   V₂ = Volume of acid           =                             ml

                                    S₂ = Strength of acid          =                             (N)         

                                                                                                                 

                V₁ S₁  =   V₂ S₂

                                       V₂ S₂

            Or,    S₁   =   ----------------  =  ------------------  =                   (N)

                                          V₁   

    

                           Strength of acid ( NaOH )  =                     (N)

           

RESULT :-

         (a)   Strength of  NaOH     0.1(N)    =                     (N)

PRECAUTION :-

                  i)   Taken necessary step should be taken to prevent the breaking of stop cork of  the burette .

                 ii)   Acid Solution from burette should be added slowly.

                iii)   Not more then 3-4 drops of Phenolphthalein is used.

                iv)   The Difference of acid Solution between two titrations should not vary more than 0.2ml. If it is high, repeat the titration.