- Preparation and standardization of solutions is essential for accurate chemical analysis.
- Below are step-by-step guides for preparing and standardizing the given molar and normal solutions.
1. Oxalic Acid (H₂C₂O₄) Solution
- Molecular weight: 126.07 g/mol
- Normality: For reactions with KMnO₄ (5e⁻), Oxalic acid is 2N (since it donates two electrons in redox reactions).
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Preparation of 0.1 M Oxalic Acid:
- Weigh 6.3035 g of oxalic acid dihydrate (H₂C₂O₄·2H₂O).
- Dissolve in distilled water and make up the volume to 1 liter.
- Mix thoroughly.
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Standardization:
- Titrate against a standard solution of sodium hydroxide using phenolphthalein as an indicator (end point: pink color).
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2. Sodium Hydroxide (NaOH) Solution
- Molecular weight: 40.00 g/mol
- Normality: For NaOH, M = N since it is monoprotic (1 OH⁻ ion per molecule).
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Preparation of 0.1 N Sodium Hydroxide:
- Weigh 4.0 g of sodium hydroxide.
- Dissolve in 1 liter of distilled water.
- Store in a sealed container to avoid absorption of CO₂ from the air.
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Standardization:
- Titrate against a standard solution of oxalic acid using phenolphthalein as an indicator. The end point is the appearance of a pink color.
3. Hydrochloric Acid (HCl) Solution
- Molecular weight: 36.46 g/mol
- Commercial HCl is usually around 37
- Concentration of stock HCl: ~12 M
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Preparation of 0.1 N Hydrochloric Acid:
- Use a volumetric calculation to dilute the stock solution:
- $V_1 = \frac{N_2 V_2}{N_1} = \frac{0.1 \times 1000}{12} \approx 8.33\,\text{mL}$
- Dilute 8.33 mL of concentrated HCl to 1 liter with distilled water.
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Standardization:
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- Titrate against a standard solution of sodium carbonate (Na₂CO₃) using methyl orange as an indicator (end point: orange).
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4. Sodium Thiosulphate (Na₂S₂O₃) Solution
- Molecular weight: 248.18 g/mol
- Sodium thiosulphate is typically used in redox titrations (Iodometric titration).
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Preparation of 0.1 N Sodium Thiosulphate:
- Weigh 24.818 g of Na₂S₂O₃·5H₂O.
- Dissolve in distilled water and dilute to 1 liter.
- Store in a cool, dark place to prevent decomposition.
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Standardization:
- Titrate against a standard solution of potassium dichromate (K₂Cr₂O₇) or potassium iodate (KIO₃) in the presence of iodine and starch as an indicator (end point: disappearance of blue color).
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5. Sulfuric Acid (H₂SO₄) Solution
- Molecular weight: 98.08 g/mol
- Concentrated H₂SO₄ is around 98
- Concentration of stock H₂SO₄: ~18 M
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Preparation of 0.1 N Sulfuric Acid:
- Use the dilution formula:
- $V_1 = \frac{N_2 V_2}{N_1} = \frac{0.1 \times 1000}{18} \approx 5.56\,\text{mL}$
- Carefully dilute 5.56 mL of concentrated H₂SO₄ to 1 liter with distilled water (add acid to water, not the reverse).
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Standardization:
- Titrate against a standard solution of sodium carbonate (Na₂CO₃) using methyl orange as an indicator (end point: orange).
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6. Potassium Permanganate (KMnO₄) Solution
- Molecular weight: 158.03 g/mol
- Potassium permanganate is a strong oxidizing agent and is used in redox titrations.
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Preparation of 0.1 N Potassium Permanganate:
- Weigh 3.1606 g of KMnO₄.
- Dissolve in distilled water and dilute to 1 liter.
- The solution needs to be standardized before use as it may decompose over time.
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Standardization:
- Titrate against a standard oxalic acid solution in acidic medium (with H₂SO₄). Heat the solution to about 70°C to accelerate the reaction. The end point is the disappearance of the purple color of KMnO₄.
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7. Ceric Ammonium Sulphate [(NH₄)₄Ce(SO₄)₄] Solution
- Molecular weight: 632.57 g/mol
- Ceric ammonium sulfate is used as an oxidizing agent in redox titrations.
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Preparation of 0.1 N Ceric Ammonium Sulphate:
- Weigh 63.257 g of ceric ammonium sulfate.
- Dissolve in 1 liter of distilled water containing a small amount of sulfuric acid (to prevent hydrolysis).
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Standardization:
- Titrate against a primary standard such as arsenious oxide (As₂O₃) in acidic conditions with ferroin as an indicator (end point: red color to pale blue).
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General Notes for Preparation and standardization of solutions:
- Glassware: Always use clean and calibrated volumetric flasks, pipettes, and burettes for accurate results.
- Indicators: Choose an appropriate indicator based on the nature of the reaction (acid-base or redox).
- Safety: Always handle concentrated acids and bases with care. Use proper personal protective equipment (PPE) like gloves and goggles.
