How to Prepare and Standardize Oxalic Acid Solution Stepwise Procedure and Calculations
The Preparation Of Standard Solution Of Oxalic Acid is an essential laboratory exercise in chemistry, particularly in volumetric analysis. This process involves accurately dissolving a calculated quantity of oxalic acid, a primary standard, into distilled water to prepare a solution of precisely known concentration. Understanding this standardization practice is vital for titration experiments and quantitative analysis in both educational settings (such as class 12 lab manual) and industrial applications.
What Is a Standard Solution?
A standard solution is a solution of known, accurate concentration, used to determine the concentration of unknown solutions in titration experiments. Oxalic acid ($ C_2H_2O_4 \cdot 2H_2O $) serves as an excellent primary standard because of its high purity and stable nature.
Key Characteristics of a Primary Standard Solution
- High purity and stability over time
- Non-hygroscopic and easy to weigh
- Known composition and molar mass
Preparation Of Standard Solution Of Oxalic Acid: Step-by-Step Procedure
Follow this procedure for accurate oxalic acid standard solution preparation:
1. Calculation of Required Amount
- First, choose the desired molarity (M) and volume (V) for your solution. Commonly, a 0.1 M solution is used for titrations.
- Calculate the mass of oxalic acid dihydrate needed using the formula: \[ \text{Mass (g)} = M \times V (\text{L}) \times \text{Molar mass} \]
- The molar mass of oxalic acid dihydrate ($ C_2H_2O_4 \cdot 2H_2O $) is 126 g/mol.
For 250 mL (0.250 L) of 0.1 M solution:
\( \text{Mass} = 0.1 \times 0.250 \times 126 = 3.15 \, \text{g} \)
2. Weighing the Oxalic Acid
- Accurately weigh 3.15 g of oxalic acid dihydrate on a balance.
- Transfer the acid into a clean beaker carefully.
3. Dissolving and Diluting
- Add approximately 50–100 mL of distilled water to the beaker to dissolve the oxalic acid fully. Stir with a glass rod.
- Once dissolved, transfer the solution to a 250 mL volumetric flask.
- Rinse the beaker with small amounts of distilled water, adding the rinsing into the flask to ensure complete transfer.
- Carefully add distilled water up to the calibration mark of the flask for precise volume.
4. Mixing and Storage
- Stopper the flask and invert it gently several times for uniform mixing.
- Label the flask clearly with concentration and date.
Diagram: Preparation Of Standard Solution Of Oxalic Acid
A labeled diagram typically illustrates weighing the acid, dissolving it, and transferring into the volumetric flask. Visual aids help in understanding the process and may be found in class 12 lab manuals or standard chemistry textbooks.
Precautions and Viva Questions
- Use only clean and dry apparatus.
- Always use distilled water to avoid contamination.
- Make sure the oxalic acid is pure and dry before weighing.
- Questions you may face in viva: Why is oxalic acid a primary standard? How do you calculate the required mass? What are the uses of a standard solution?
Applications of Oxalic Acid Standard Solution
- As a titrant in redox titration, particularly with potassium permanganate (KMnO4)
- In analytical chemistry for quantitative analysis of substances
For more details about the properties and uses of oxalic acid, visit oxalic acid properties and uses. You can also understand more about redox titration principles and the nature of acids, bases, and salts for further reading.
Conclusion
Accurate preparation of standard solution of oxalic acid is fundamental for quantitative analytical chemistry. Mastery of this process ensures reliable results in titration and other procedures that depend on precise solution concentrations. From correct calculation to thorough mixing, every step is critical to success—making this a core skill for students and professionals. Understanding the process also helps you answer common viva questions and excel in practical exams. To gain a deeper understanding of solutions in chemistry, refer to this comprehensive guide on solutions in chemistry.
FAQs on Preparation of Standard Oxalic Acid Solution for Titration
1. What is the preparation of standard solution of oxalic acid?
The preparation of standard solution of oxalic acid is the process of accurately weighing pure oxalic acid and dissolving it in a definite volume of distilled water to obtain a solution of known concentration. In laboratory practice, oxalic acid dihydrate H2C2O4·2H2O is commonly used as a primary standard.
- Accurately weigh the required mass of oxalic acid crystals.
- Dissolve in distilled water in a beaker.
- Transfer to a volumetric flask and make up to the mark.
- Shake well to ensure uniform concentration.
2. Why is oxalic acid used as a primary standard solution?
Oxalic acid is used as a primary standard because it is pure, stable, non-hygroscopic, and has a high molar mass. These properties make it suitable for preparing an accurate standard solution.
- Available in highly pure crystalline form as H2C2O4·2H2O.
- Does not absorb moisture easily from air.
- Can be weighed accurately.
- Completely soluble in water.
3. What is the chemical formula of oxalic acid used in standard solution preparation?
The chemical formula of oxalic acid used in laboratory standard solution preparation is H2C2O4·2H2O, known as oxalic acid dihydrate. It contains two molecules of water of crystallization.
- Molar mass of oxalic acid dihydrate ≈ 126 g mol-1.
- It is a diprotic acid, meaning it can donate two H+ ions.
4. How do you prepare 0.1 M oxalic acid solution?
To prepare 0.1 M oxalic acid solution, dissolve 12.6 g of oxalic acid dihydrate in water and make the volume up to 1 litre. This is calculated using the molar mass 126 g mol-1.
- Molarity (M) = moles / volume (L).
- Required moles for 1 L of 0.1 M solution = 0.1 mol.
- Mass = 0.1 × 126 = 12.6 g.
- Dissolve in distilled water and make up to 1 L in a volumetric flask.
5. What is the procedure for preparation of standard solution of oxalic acid in the laboratory?
The laboratory procedure involves accurate weighing, dissolution, and dilution of oxalic acid to a fixed volume to obtain a standard solution. The steps are:
- Weigh the calculated mass of H2C2O4·2H2O using an analytical balance.
- Dissolve it in a small amount of distilled water in a beaker.
- Transfer the solution into a volumetric flask using a funnel.
- Rinse the beaker and add washings to the flask.
- Make up the volume to the calibration mark with distilled water.
- Stopper and shake well for uniform mixing.
6. How do you calculate the mass of oxalic acid required for a standard solution?
The mass of oxalic acid required is calculated using the formula Mass = Molarity × Molar mass × Volume (in L). For oxalic acid dihydrate, molar mass = 126 g mol-1.
- Example: For 250 mL (0.25 L) of 0.1 M solution:
- Mass = 0.1 × 126 × 0.25 = 3.15 g.
7. What is the reaction of oxalic acid with sodium hydroxide in titration?
Oxalic acid reacts with sodium hydroxide in a neutralization reaction to form sodium oxalate and water. The balanced chemical equation is: H2C2O4(aq) + 2NaOH(aq) → Na2C2O4(aq) + 2H2O(l).
- Oxalic acid is a diprotic acid.
- 1 mole of oxalic acid reacts with 2 moles of NaOH.
8. What precautions should be taken while preparing standard oxalic acid solution?
Key precautions include accurate weighing, proper transfer, and correct volume adjustment to ensure a reliable standard solution. Important points are:
- Use a clean and dry weighing bottle.
- Weigh using an analytical balance for precision.
- Ensure complete dissolution before making up the volume.
- Add distilled water up to the calibration mark at eye level.
- Shake the volumetric flask thoroughly after dilution.
9. What is the difference between molarity and normality of oxalic acid solution?
Molarity is the number of moles per litre, while normality is the number of equivalents per litre of solution. For oxalic acid, which is diprotic, 1 mole provides 2 equivalents.
- Molarity (M) = moles of solute / litre of solution.
- Normality (N) = equivalents of solute / litre of solution.
- For oxalic acid: Normality = 2 × Molarity.
10. What is the importance of preparing a standard solution of oxalic acid?
The importance of preparing a standard solution of oxalic acid lies in its use for accurate volumetric analysis and standardization of bases. It serves as a reliable reference solution in titration experiments.
- Used to standardize NaOH and other strong bases.
- Helps determine unknown concentrations.
- Ensures accuracy in quantitative chemical analysis.
