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Standardization of KOH with Oxalic Acid


STANDARDISATION OF KOH (POTASSIUM HYDROXIDE) WITH OXALIC ACID


Determine the normality of the given solution of KOH using standard oxalic acid solution containing 6.2 gL-1

Principle:


The determination of normality is based on the reaction between KOH and oxalic acid as shown by the equation given below.


2KOH + H2C2O4  K2C2O4 + 2H2O


Here one mole of oxalic acid (two equivalents) reacts with two moles of KOH. Therefore, the equivalent mass of KOH is the same as its molecular mass (56).


Equivalent Mass of Oxalic acid = Molecular Mass/2 = 126/2 = 63

Equivalent Mass of KOH = Molecular Mass = 56


A known volume of KOH solution is titrated against the standard oxalic acid solution using phenolphthalein as the indicator. From the titre values, the normality and the mass per litre of KOH are calculated.


Indicator

End point

In burette

In pipette

Phenolphthalein

Pink to colourless

Oxalic acid solution

Potassium hydroxide solution

 

Procedure:


20 mL of the potassium hydroxide solution is pipetted out into a clean conical flask after rinsing the pipette with the same solution. One or two drops of phenolphthalein are added to it. It is then titrated against oxalic acid taken in the burette. The addition of acid is continued till the colour of the solution fades. The sides of the conical flask are washed with small quantities of water using a wash bottle. The titration is continued by adding acid in drops till the pink colour just disappears with a last single drop of acid. The end point is the disappearance of the pink colour. The titration is repeated to get concordant values. The results are tabulated as shown below. From the values, the normality and the mass per litre of KOH are calculated.


KOH x H2C2O4


Expt. No:

Volume of KOH

Burette reading

Volume of H2C2O4

Initial               

Final

1

2

3

20

20

20

 

 

 


Calculation


Volume of KOH solution, V1 = 20 mL

Let normality of KOH solution = N1

Normality of H2C2O4, N2 = Mass per litre/Eq. Mass = 6.2/63 = 0.0984

Let volume of H2C2O4 = V2 mL

N1 x V1 = N2 x V2

Normality of KOH, N1 = V2 x 0.0984/20

Mass per litre of KOH = N1 x 56g


Result


Normality of KOH = _____

Mass per litre of KOH = _____ g


NOTE:


Acidimetry: Acidimetry is the estimation of an alkali solution using a standard acid solution.


Alkalimetry: Alkalimetry is the estimation of an acid solution using a standard alkali solution. When an acid reacts with a base neutralization reaction takes place resulting in the formation of a salt and water. If both acid and base are strong then the resulting solution at the end point is neutral with pH = 7. On the other hand, if the acid or base is weak then the salt formed by the neutralization will undergo hydrolysis and the solution at the end point will be slightly alkaline or acidic. The indicators used in acidimetry and alkalimetry are phenolphthalein and methyl orange. These indicators are weak organic acids or bases. In acid-base titrations, acid should be taken in the burette and the base should be pippetted out into a conical flask.


A few other experiments in acidimetry and alkalimetry,


1. Determine the normality and the mass per litre of nitric acid using a standard solution of sodium hydroxide containing 4.1 gL-1.


2. Determine the strength and the mass per litre of sulphuric acid. You are provided with a standard solution of potassium hydroxide containing 5.5 gL-1.


3. Determine the normality and mass per litre of sodium carbonate. You are provided with hydrochloric acid solution containing 3.7 gL-1.


4. Determine the mass per litre of hydrochloric acid. You are supplied with a standard with a standard solution of potassium carbonate containing 7.0 gL-1.

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