Step-by-Step Procedure for Making a Standard Oxalic Acid Solution
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 How to Prepare a Standard Solution of Oxalic Acid
1. What is a standard solution of oxalic acid?
A standard solution of oxalic acid is a solution with a known, precise concentration of oxalic acid (H2C2O4), typically used in titration experiments. To prepare it accurately, use a weighed amount of oxalic acid dihydrate dissolved in a measured volume of distilled water, ensuring the solution’s molarity matches syllabus and practical needs.
2. How do you prepare a standard solution of oxalic acid in the laboratory?
Preparation of standard oxalic acid solution involves dissolving a specific mass of oxalic acid dihydrate in distilled water. Steps include:
- Weigh approximately 6.3 g of oxalic acid dihydrate (H2C2O4·2H2O)
- Dissolve it in about 50-80 mL of distilled water in a beaker
- Transfer into a 250 mL volumetric flask
- Rinse the beaker and add rinsing to the flask
- Make up the volume to the mark with distilled water
- Stopper and shake the flask to mix thoroughly
3. Why is oxalic acid used as a primary standard?
Oxalic acid is used as a primary standard because it can be obtained in pure, stable, and crystalline form, making precise weighing easy. Key reasons:
- High purity and stability
- Non-hygroscopic nature
- Known composition and molar mass
- Does not react with air or atmospheric gases
4. What precautions should be taken while preparing a standard solution of oxalic acid?
When preparing a standard solution of oxalic acid, observe these precautions:
- Use only primary standard grade oxalic acid dihydrate
- Weigh accurately to avoid errors
- Dissolve fully before transferring to the volumetric flask
- Ensure the flask is clean and dry
- Make up to the mark only at eye level
- Avoid spillage and rinsing loss
5. How do you calculate the molarity of the prepared oxalic acid solution?
To calculate the molarity of oxalic acid solution, use the formula:
- Molarity (M) = Number of moles of solute / Volume of solution in litres
- Number of moles = Mass of oxalic acid (g) / Molar mass (g/mol)
- For 6.3 g of oxalic acid dihydrate in 250 mL, molarity = (6.3/126) / 0.25 = 0.2 M
6. What is the role of volumetric flask in preparing standard solutions?
Volumetric flasks are essential for preparing standard solutions because they allow precise measurement of total solution volume. Their calibrated narrow neck ensures accurate dilution to an exact volume, which is crucial for obtaining correct solution concentration as required by the CBSE practical syllabus.
7. What is the normality of a standard oxalic acid solution prepared from 6.3 g oxalic acid dihydrate in 250 mL?
The normality (N) of a standard oxalic acid solution can be calculated as follows:
- Moles = 6.3/126 = 0.05 mol
- Since oxalic acid is dibasic, Normality = 0.05 × 2 / 0.25 = 0.4 N
- Thus, the solution is 0.4 N oxalic acid solution
8. Which apparatus are required for preparing a standard solution of oxalic acid?
To prepare a standard oxalic acid solution, the following apparatus are needed:
- Weighing balance (for measuring oxalic acid)
- Watch glass
- Beaker
- Glass rod
- Volumetric flask
- Funnel
- Distilled water
9. What are the common errors while preparing a standard solution and how can they be minimized?
Common errors in preparing standard solutions of oxalic acid include:
- Inaccurate weighing (use a precise electronic balance)
- Incomplete transfer of solute (rinse beaker thoroughly)
- Incorrect volume adjustment (ensure flask is filled up to the calibration mark at eye level)
- Use of impure or moist chemicals (use only analytical grade reagents)
10. Why is distilled water used to prepare standard solutions?
Distilled water is used in preparing standard solutions because it is free from impurities, ions, or contaminants that could affect the accuracy and consistency of the standard solution, ensuring reliable results in titrations and experiments.
11. What is the principle behind preparing standard solutions for titration?
The principle is to prepare a solution of known concentration that can accurately react with another substance in a solution of unknown concentration. This allows calculation of the unknown by stoichiometry, as per CBSE Chemistry practical examination standards.
12. How do you store a standard solution of oxalic acid?
Standard oxalic acid solution should be stored in a clean, labeled glass bottle, tightly stoppered and kept away from sunlight and heat sources to maintain stability, as per laboratory best practices and syllabus requirements.
