Sodium hydroxide: Preparation and standardization of molar and normal solutions
Sodium hydroxide (NaOH) is a strong base that is commonly used in the preparation of molar and normal solutions. Here is a general procedure for the preparation and standardization of a 0.1 M sodium hydroxide solution and a 0.1 N sodium hydroxide solution:
Preparation of 0.1 M sodium hydroxide solution:
- Weigh 4 g of sodium hydroxide pellets using an analytical balance and transfer them to a 1-liter volumetric flask.
- Add about 800 mL of distilled water to the flask and swirl gently to dissolve the sodium hydroxide.
- Once the sodium hydroxide is completely dissolved, add more distilled water until the solution reaches the 1-liter mark on the flask.
- Cap the flask and mix the solution thoroughly to ensure uniformity.
Standardization of 0.1 M sodium hydroxide solution:
- Weigh about 0.5 g of primary standard potassium hydrogen phthalate (KHP) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
- Add about 50 mL of distilled water to the flask and swirl gently to dissolve the KHP.
- Add a few drops of phenolphthalein indicator to the solution.
- Titrate the KHP solution with the 0.1 M sodium hydroxide solution until a pink color is observed.
- Record the volume of the sodium hydroxide solution used for the titration.
Calculation:
The molar mass of KHP is 204.22 g/mol. The equation for the reaction between KHP and sodium hydroxide is:
KHP + NaOH → NaKP + H2O
From the balanced equation, we know that 1 mole of KHP reacts with 1 mole of sodium hydroxide. Therefore, the number of moles of sodium hydroxide can be calculated from the volume of sodium hydroxide solution used in the titration and the molarity of the solution.
The weight of KHP used in the titration can also be used to calculate the molarity of the sodium hydroxide solution.
Standardization of 0.1 N sodium hydroxide solution:
- Weigh about 0.3 g of primary standard oxalic acid dihydrate (C2H2O4·2H2O) using an analytical balance and transfer it to a clean, dry Erlenmeyer flask.
- Add about 50 mL of distilled water to the flask and swirl gently to dissolve the oxalic acid.
- Add a few drops of phenolphthalein indicator to the solution.
- Titrate the oxalic acid solution with the 0.1 N sodium hydroxide solution until a pink color is observed.
- Record the volume of the sodium hydroxide solution used for the titration.
Calculation:
The molar mass of C2H2O4·2H2O is 126.07 g/mol. The equation for the reaction between oxalic acid and sodium hydroxide is:
H2C2O4 + 2 NaOH → Na2C2O4 + 2 H2O
From the balanced equation, we know that 2 moles of sodium hydroxide react with 1 mole of oxalic acid. Therefore, the number of moles of sodium hydroxide can be calculated from the volume of sodium hydroxide solution used in the titration and the normality of the solution.
The weight of C2H2O4·2H2O used in the titration can also be used to calculate the normality of the sodium hydroxide solution.
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