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Chapter: 12th Chemistry : Practicals

Estimation of sodium hydroxide

To estimate the amount of sodium hydroxide dissolved in 250 ml of the given unknown solution volumetrically.

Estimation of sodium hydroxide

 

Aim :

To estimate the amount of sodium hydroxide dissolved in 250 ml of the given unknown solution volumetrically. For this you are given with a standard solution of sodium carbonate solution of normality 0.0948 N and hydrochloric acid solution as link solution.

 

Principle:

Neutralization of Sodium carbonate by HCl is given below. To indicate the end point, methyl orange is used as an indicator.

Na2CO3  + 2HCl 2NaCl + CO2  + H2O

Neutralization of Sodium hydroxide by HCl is given below. To indicate the end point, phenolphthalein is used as an indicator.

NaOH + HCl NaCl + H2O

 

Short procedure:


 

Procedure :

Titration–I

(Link HCl )Vs (standard Na2CO3)

Burette is washed with water, rinsed with HCl solution and filled with same HCl solution up to the zero mark. Exactly 20 ml of standard Na2CO3solution is pipetted out into the clean, washed conical flask. To This solution 2 to 3 drops of methyl orange indicator is added and titrated against HCl link solution from the burette. HCl is added drop wise till the colour change from straw yellow to pale pink. Burette reading is noted and the same procedure is repeated to get concordant values.

Titration –I

(Link HCl )Vs (standard Na2CO3)


 

Calculation :

Calculation :                           

Volume of  HCl (link) solution         V1      =       ml

Normality HCl (link) solution N1      =       ? N

Volume of standard Na2CO3 solution         V2      =       20 ml

Normality of standard Na2CO3 solution     N2      =       0.0948 N

 

According to normality equation:

According to normality equation: V1× N1 = V2 × N2

N1 = V2 × N2 / V1


Normality of HCl (link) solution (N1) = ------------X--------- N

Titration–II

(Unknown NaOH ) Vs (Link HCl)

Burette is washed with water, rinsed with HCl solution and filled with same HCl solution up to the zero mark. Exactly 20 ml of unknown NaOH solution is pipetted out into the clean, washed conical flask. To This solution 2 to 3 drops of phenolphthalein indicator is added and titrated against HCl link solution from the burette. HCl is added drop wise till the pink colour disappears completely. Burette reading is noted and the same procedure is repeated to get concordant values.

Titration –II

(Link HCl )Vs (Unknown NaOH solution)


 

Calculation :

Volume of Unknown NaOH solution         V1      =       20 ml

Normality of Unknown NaOH solution     N1      =       ? N

Volume of  HCl (link) solution         V2      =       ml

Normality HCl (link) solution N2      =       N

According to normality equation:

V1 x N1 = V2  x N2

N1  = V2  x N2  / V1


Normality of Unknown HCl solution N1  = __________Y_____ N

 

Weight calculation:

The amount of NaOH dissolved in 1 lit of the solution = (Normality) x (equivalent weight)

The amount of NaOH dissolved in 250 ml of the solution = Normality x equivalentweight x 250 / 1000

=  Y × 40 × 250 / 1000


 

Report :

The amount of NaOH dissolved in 750 ml of the solution      =       g


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