Preparation and standardization of sulfuric acid

BACKGROUND

It is an acid-base titration. The sulfuric acid is an acid whose strength changes over time and it can be effectively standardized utilizing pre-standardized sodium hydroxide. H₂SO₄ react with NaOH in presence of methyl orange indicator. The color changes from yellow to orange at the end point.¹

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Hence, based on the above theory our aim is to prepare and standardize sulfuric acid with sodium hydroxide solution.

REQUIREMENTS

Apparatus:     

• Cleaned and calibrated pipette
• Burette
• Conical flask

Chemicals:     

• Conc. sulfuric acid – 96%
• Sodium hydroxide AR grade
• Oxalic acid AR grade
• Methyl orange indicator
• Phenolphthalein 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 = 1 M NaOH

            4 g of NaOH dissolved in 1000 ml water = 0.1 M NaOH

Preparation of oxalic acid solution

            Molecular weight of oxalic acid =126 g

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

            126 g of oxallic acid dissolved in 1000 ml water = 1M oxalic acid

            1.26gm of oxallic acid dissolved in 1000 ml water = 0.1 N oxalic acid

Preparation of sulfuric acid solution

            Molecular weight of conc. H₂SO₄ =98.09 g

            Molarity of conc. H₂SO₄ =18 M (density 1.8 g/ml)

            Volume of conc. H₂SO₄ required = 5.67 ml

    Therefore, 5.67 ml of conc. H₂SO₄ dissolved in 1000ml water gives 0.1 M H₂SO₄

Standardization of sodium hydroxide

Transfer 20 ml of 0.1 M oxalic acid to a conical flask and add 2 drops of phenophthalein indicator. Titrate with sodium hydroxide from the burette. Note the end point, when a light pink color will be observed. Repeat the experiment until three concordant readings.

Tabulation for standardization of sodium hydroxide using oxalic acid

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.

        M₁V₁ = M₂V₂

        M₂=Molarity of oxalic acid, M₁=Molarity of NaOH.

        V₂=Volume of oxalic acid, V₁=Volume of NaOH

        M₁=M₂V₂/V₁

Standardization of sulfuric acid

Take 20 ml of sodium hydroxide solution into a clean conical flask with addition of 2-3 drops of methyl orange indicator. Perform titration with H₂SO₄ present in burette. Note the end point when yellow color changes to orange color. Repeat the experiment with two successive readings are concurrent.

Tabulation for standardization of sulfuric acid using standard sodium hydroxide solution

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

        M₂V₂ = M₃V₃

        M₂=Normality of Oxalic acid, M₃=Normality of Sulfuric acid

        V₂=Volume of Oxalic acid, V₃=Volume of Sulfuric acid

        M₃=M₂V₂/V₃

CONCLUSION

From the above experiment it is evident that sulfuric acid can be effectively standardized by using sodium hydroxide and methyl orange as the visual indicator. However, the sodium hydroxide needs to be pre-standardized using a primary standard oxalic acid using phenolphthalein as the indicator. After performing the calculations, strength of the prepared sodium hydroxide solution was found to be……..N.

REFERENCES

1. Kasture AV, Wadodkar SG, Gokhale SB. Practical Pharmaceutical Chemistry-I. Nirali Prakashan; 1993: 47.

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