Introduction
Sulfuric acid (H₂SO₄) is a highly corrosive, strong acid widely used in chemical laboratories, industries, and analytical applications. Preparing and standardizing H₂SO₄ molar and normal solutions is crucial for maintaining accuracy in titrations, chemical reactions, and industrial processes. This guide provides a step-by-step approach to preparing and standardizing sulfuric acid solutions with high precision.
What is Sulfuric Acid (H₂SO₄)?
Sulfuric acid is a strong diprotic acid commonly used in:
- Titrations (as a standard acid in acid-base reactions)
- Chemical manufacturing (fertilizers, dyes, and pharmaceuticals)
- Batteries (lead-acid batteries in vehicles)
- Industrial cleaning and etching
Since sulfuric acid is a highly concentrated and hazardous chemical, proper handling, storage, and preparation procedures are essential.
Understanding Molarity and Normality of H₂SO₄
- Molarity (M): Number of moles of H₂SO₄ per liter of solution.
- Normality (N): Number of gram-equivalent weights of H₂SO₄ per liter of solution.
Sulfuric acid is a diprotic acid, meaning it donates two protons (H⁺) per molecule in a reaction.
Thus, 1M H₂SO₄ = 2N H₂SO₄ in acid-base titrations.
Preparation of Sulfuric Acid (H₂SO₄) Molar and Normal Solutions
1. Materials Required
- Concentrated sulfuric acid (98% H₂SO₄, density = 1.84 g/mL)
- Distilled water
- Analytical balance
- Volumetric flask (1L)
- Pipette and measuring cylinder
- Glass rod
- Safety gear (gloves, goggles, lab coat, fume hood)
2. Calculation for H₂SO₄ Solution Preparation
The molar mass of H₂SO₄ is 98.08 g/mol, and the concentrated sulfuric acid (98%) has a density of 1.84 g/mL.
Using the formula:
Thus, 54.4 mL of concentrated sulfuric acid is needed to prepare 1L of 1M H₂SO₄ solution.
For a 0.1M H₂SO₄ solution, use 5.44 mL of concentrated H₂SO₄ per liter.
3. Procedure for Preparation
⚠ Caution: Always add acid to water, NEVER the reverse.
- Take 500 mL of distilled water in a 1L volumetric flask.
- Slowly add 54.4 mL of concentrated H₂SO₄ while stirring continuously.
- Allow the solution to cool, as the reaction is highly exothermic.
- Make up the volume to 1L with distilled water.
- Mix well and store in a properly labeled bottle.
⚠ Safety Note: Always prepare sulfuric acid solutions in a fume hood while wearing protective gear.
Standardization of Sulfuric Acid (H₂SO₄) Solution
Since sulfuric acid absorbs moisture from the air, it must be standardized using a primary standard such as sodium carbonate (Na₂CO₃) or potassium hydrogen phthalate (KHP).
1. Materials Required for Standardization
- Prepared H₂SO₄ solution
- Sodium carbonate (Na₂CO₃) (Primary standard)
- Methyl orange indicator
- Pipette and burette
- Conical flask and distilled water
2. Reaction Equation
The standardization is based on the neutralization reaction:
3. Procedure for Standardization
- Weigh 0.53g of anhydrous Na₂CO₃ and dissolve it in 100 mL of distilled water.
- Pipette 25 mL of Na₂CO₃ solution into a conical flask.
- Add 2-3 drops of methyl orange indicator (solution turns yellow).
- Titrate with H₂SO₄ solution from the burette until the color changes from yellow to faint pink.
- Record the final burette reading and repeat for accuracy.
4. Calculation of Standardized Molarity
Using the titration formula:
This determines the exact concentration of the sulfuric acid solution.
Applications of Standardized Sulfuric Acid Solution
- Acid-base titrations in analytical chemistry.
- Manufacturing of fertilizers, dyes, and detergents.
- Electrolyte in lead-acid batteries.
- Used in petroleum refining and metal processing.
Conclusion
The preparation and standardization of sulfuric acid (H₂SO₄) molar and normal solutions are essential for precise analytical work in laboratories and industries. Proper handling and strict adherence to safety protocols ensure accurate titration results and solution stability. Since sulfuric acid is hygroscopic, it should be standardized periodically to maintain consistent concentration and reliability in chemical reactions, titrations, and industrial applications. By mastering these preparation and standardization techniques, laboratories can ensure high precision, reproducibility, and compliance with analytical standards.
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