Oxalic acid: Preparation and standardization of molar and normal solutions
Oxalic acid is a dicarboxylic acid 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 oxalic acid solution and a 0.1 N oxalic acid solution:
Preparation of 0.1 M oxalic acid solution:
- Weigh 1.26 g of oxalic acid dihydrate (C2H2O4·2H2O) using an analytical balance and transfer it to a 1-liter volumetric flask.
- Add about 800 mL of distilled water to the flask and swirl gently to dissolve the oxalic acid.
- Once the oxalic acid 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 oxalic acid 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 oxalic acid solution until a pale pink color is observed.
- Record the volume of the oxalic acid solution used for the titration.
Calculation:
The molar mass of KHP is 204.22 g/mol. The equation for the reaction between KHP and oxalic acid is:
KHP + H2C2O4 → KHC2O4 + H2O
From the balanced equation, we know that 1 mole of KHP reacts with 1 mole of oxalic acid. Therefore, the number of moles of oxalic acid can be calculated from the volume of oxalic acid 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 oxalic acid solution.
Standardization of 0.1 N oxalic acid solution:
- Weigh about 0.8 g of sodium carbonate (Na2CO3) 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 sodium carbonate.
- Add a few drops of methyl orange indicator to the solution.
- Titrate the sodium carbonate solution with the 0.1 N oxalic acid solution until the solution turns from yellow to pink.
- Record the volume of the oxalic acid solution used for the titration.
Calculation:
The molar mass of Na2CO3 is 105.99 g/mol. The equation for the reaction between Na2CO3 and oxalic acid is:
Na2CO3 + H2C2O4 → Na2C2O4 + H2O + CO2
From the balanced equation, we know that 2 moles of Na2CO3 react with 1 mole of oxalic acid. Therefore, the number of moles of oxalic acid can be calculated from the volume of oxalic acid solution used in the titration and the normality of the solution.
The weight of Na2CO3 used in the titration can also be used to calculate the normality of the oxalic acid solution.
Note: It is important to perform the calculations carefully and accurately, as any errors in the preparation or standardization of the solutions can affect the accuracy
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