Preparation and standardization of sodium hydroxide

BACKGROUND

It is an acid-base titration. The sodium hydroxide is an alkali whose strength changes over time and it can be effectively standardized utilizing primary standard viz. oxalic acid. Sodium hydroxide reacts with oxalic acid in presence of phenolphthalein indicator. The color changes from colorless to pink at the end point.¹

Hence, based on the above theory our aim is to prepare and standardize sodium hydroxide using oxalic acid.

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REQUIREMENTS

Apparatus:     Cleaned and calibrated pipettes, Burettes, Conical flasks

Chemicals:     Sodium hydroxide AR Grade, Oxalic acid AR Grade, Phenolpthalene indicator

PROCEDURE

Preparation of sodium hydroxide solution

            Molecular weight of NaOH = 40 g

            Equivalent weight of NaOH = 40/1 = 40 g

            40 g of NaOH dissolved in 1000 ml water = 1N NaOH

            20 g of NaOH dissolved in 1000 ml water = 0.5 N NaOH

Preparation of oxalic acid solution

            Molecular weight of oxalic acid = 126gm

            Equivalent weight of oxalic acid = 126/2=63gm

            63 g of oxallic acid dissolved in 1000ml water = 1 N oxalic acid

            31.5 g of oxallic acid dissolved in 1000ml water = 0.5 N oxalic acid

Standardization

Transfer 20 ml of 0.5 N oxalic acid to a conical flask. Add 2-3 drops of phenolphthalein indicator and titrate with sodium hydroxide present in the burette. Note the end point when a pale pink color is observed. Repeat the experiment until three concordant reading.

Tabulation for standardization

Sl. No.	Volume of Oxalic acid taken (ml)	Burette reading of sodium hydroxide (ml)		Volume of Sodium hydroxide consumed (ml)
		IR	FR
1.
2.
3.

Calculation

N₁V₁ = N₂V₂

N₂=Normality of oxalic acid, N₁=Normality of NaOH, V₂=Volume of Oxalic acid, V₁=Volume of NaOH

=> N₁=N₂V₂/V₁

CONCLUSION

From the above experiment it was evident that sodium hydroxide can be effectively standardized by using oxalic acid. Addition of phenolphthalein indicator helped in easy detection of the end point. After performing the calculations, strength of the prepared sodium hydroxide solution was found to be……..N.

REFERENCES

1. Available at: http://www.webhosting.au.edu/basic-science/subjects/chemistry%20lab/experiments/12010/BG%200008-week312010.pdf. Accessed on 23 August 2017.
   

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