Chemistry Experiment: To Prepare 250 ml of M/10 Solution of Oxalic Acid From Crystalline Oxalic Acid
What is oxalic acid? Oxalic acid is a chemical compound that has the chemical formula ${{C}_{2}}{{H}_{2}}{{O}_{4}}$ and bears the IUPAC name ethanedioic acid. It's considered the simplest dicarboxylic acid. A white crystalline solid forms a colourless solution once dissolved in water. The standard solution of ethanedioic acid is a known high-purity substance that may be dissolved to provide a primary standard solution in a known volume of solvent.
In the preparation of oxalic acid, several known solvent weights are dissolved. It's prepared using a standard, like a standard primary substance. Let us look into the preparation of ethanedioic acid solution.
Table of Content
Aim
Material Required
Theory
Procedure
Result
Observation
Precautions
Viva Questions
Summary
Aim
To prepare 250 ml of M/10 solution of oxalic acid from crystalline oxalic acid.
Materials Required
Weighing Tube
Watch Glass
Measuring Flask
Beaker (250 ml)
Glass Rod
Chemical Balance
Wash Bottle
Funnel
Funnel Stand
Distilled Water
Oxalic Acid
Theory
Many acids are obtainable in concentrated form, as they're required to be used in diluted type. Thus, they're mixed with water to acquire the required volume of diluted acid. Suppose the concentration of the concentrated acid is known. In that case, we can simply determine the volume of that individual acid that must be diluted to prepare a particular volume of dilute acid of the required concentration.
We can calculate the volume of the sample acid if the molarity of the targeted acid is known to us, the following molarity equation may be used to determine the molarity of the concentrated acid as described below:-
${{M}_{1}}{{V}_{1}}={{M}_{2}}{{V}_{2}}$
Where,
M is the molarity of the concentrated acid
V1 is the volume of concentrated acid,
M2 is the molarity of dilute acid,
V2 is the volume of dilute acid.
Suppose the normality of the targeted acid is known to us. In that case, the calculation for the amount of the acid needed is completed by the following formula:
${{N}_{1}}{{V}_{1}}={{N}_{2}}{{V}_{2}}$
Where,
The normality of concentrated acid is N1
V1 is the volume of concentrated acid
N2 is the normality of dilute acid,
V2 is the volume of dilute acid.
Formula for hydrated ethanedioic acid is ${{C}_{2}}{{H}_{4}}{{O}_{4}}.2{{H}_{2}}O$ .
2.6 g of ethanedioic acid/litre of the solution ought to be dissolved to produce an M/10 oxalic acid solution.
On the other hand, 12.6 /4 = 3.15 g of crystals of ethanedioic acid (oxalic acid) should be dissolved in water, and 250 millilitres of the solution should be precisely made.
Procedure
Take a watch glass, wash it with Distilled water, and dry it properly.
Weigh the precise amount of dried and clean watch glass and record its weight in the notebook.
Weigh accurately on the watch glass 3.15 g of oxalic acid and note this weight inside the notebook.
Transfer oxalic acid softly and thoroughly with the help of a funnel from the watch glass into a clean and dry measuring flask.
Transfer gently and carefully the oxalic acid from the watch glass into a clean 250-milliliter beaker.
Wash the watch glass with distilled water using a wash bottle to transfer the particles sticking to it into the beaker.
Dissolve oxalic acid crystals within the beaker by gently stirring with a clean glass rod.
When the oxalic acid within the beaker is dissolved, carefully transfer the complete solution into a 250 ml measuring flask (volumetric flask) with a funnel
Wash the beaker with distilled water. Transfer the solution mixture into the measuring flask.
Finally, wash the funnel well with distilled water with the help of a wash bottle to transfer the solution left over to the funnel into the measuring flask.
Add enough water to the measurement flask carefully, up to just below the etched mark thereon, with the help of a wash bottle.
Add the last few drops of distilled water with a pipette till the lower level of the meniscus simply touches the mark on the measuring flask
Stopper the measuring flask and shake gently to create the solution uniform throughout.
Label it as an oxalic acid solution. Now, calculate it as a solution of oxalic acid M/10.
Observations
Result
250ml of (M/10) or 0.1 M solution of oxalic acid is prepared.
Precautions
Following precautions ought to be taken while finishing the experiment:
Wash the watch glass carefully, making sure that not even one crystal of oxalic acid is left on the watch glass.
Using a pipette, add the remaining few drops to avoid an additional addition of distilled water to the mark above the neck of the measuring cylinder.
If it's required to titrate oxalic acid or oxalate, add the required dilute amount of H2SO4 and heat the flask at a range of 60° - 70° C.
Lab Manual Questions
1. Why does oxalic acid solution boil before titration?
Ans. We heat the oxalic acid solution because without heat it's a slow method with much more energy than the activation power required to react. Thus to increase energy, the temperature ought to be increased which is only attainable by heating the oxalic acid solution.
2. What is the principle behind the estimation of oxalic acid?
Ans. Estimation is based on the reaction between KMnO4 and Oxalic acid. KMnO4 oxidizes oxalic acid in the presence of acid and while hot. Approximately 0.8g of oxalic acid is weighed, transferred into a 250 mL standard flask, and made up to the mark.
3. Does oxalic acid dissolve in hot water?
Ans. Oxalic acid crystals dissolve more readily in hot water than in a sugar solution. Tip: dissolve the oxalic crystals within the indicated amount of hot (150˚F) water before adding the sugar. Once the oxalic crystals are dissolved, only then stir in the sugar.
4. Is titration affected by temperature?
Ans. A temperature change will change the equilibrium constant, which can affect titrations in shifting equilibria in one direction or the other, adding sources of error in the titration process.
Viva Questions
Q1. Is oxalic acid a strong acid?
Ans. As an organic acid, oxalic acid could be a weak acid. Oxalic acid is understood to be a soft acid. It’s weaker than (water) H3O+ atoms. However, it's better than acetic acid, sulphuric acid, nitrous acid, carboxylic acid, etc.
Q2. Describe the procedure for the preparation of 1 normal oxalic acid.
Ans. If you dissolve ninety g of acid in 1 liter of water, it'll be 1 normal (N). To make 0.1 N, you wish to dissolve nine g of oxalic acid in one liter. If you wish to create one Molar acid, you ought to dissolve ninety g of acid in one kg of water.
Q3. How to prepare 250 ml of M/20 solution of oxalic acid?
Ans. The molecular weight of oxalic acid is 126g.
Therefore, to prepare 250 ml M/20 oxalic acid solution:
(126×250)÷(20×1000) = 1.575 grams of oxalic acid is to be dissolved in water in a 250 ml volumetric flask.
Q4. Why is the standard solution always prepared in a volumetric flask?
Ans. A volumetric flask is employed when it's necessary to understand the volume of the solution prepared exactly and accurately. Volumetric flasks are calibrated (standardised) to specific volumes. This allows scientists to see how much liquid is contained in a specific flask once it's filled.
Q5. What is the standard solution?
Ans. A standard solution of known concentration is what the quality solution is called. Normal solutions are often created by dissolving a known quantity of the substance in a specific solvent volume.
Summary
Oxalic acid, also called ethanedioic acid. It's a white crystalline solid that dissolves in water to generate a colourless solution. We can calculate the volume of the acid required to make a particular volume of the dilute solution if the molarity or normality of the concentrated acid is given and how 1M oxalic acid preparation is performed.
Practical Questions
1. Why does oxalic acid dissolve in water?
Ans. The slightly charged ends of water molecules attract these ions. As a result, the ions are dissociated or separated by the water molecules and spread equally throughout the solution.
2. What is the SI unit of normality?
Ans. Normality is represented by the letter “N.” The gram/liter is the SI unit.
3. What is known as normality?
Ans. We define normality as the number of grams equivalent to solute present in a one-litre solution. So, the unit of normality is gram/litre. we tend to denote normality with the letter 'N'.
4. Where is normality used?
Ans. Normality is usually used in acid-base chemical reactions, oxidation-reduction reactions, and precipitation reactions. Thus it refers to the chemical process. Equivalent concentration refers to the solution's reactive capacity.
5. What is the endpoint in titration?
Ans. Endpoint: the point during a titration when an indicator shows that the amount of reactant necessary for a complete reaction has been added to a solution.
FAQs on Preparation of Solution of Oxalic Acid
1. What is the most accurate method to prepare a standard 250 ml M/10 solution of oxalic acid for board examinations?
To prepare a standard 250 ml M/10 (0.1 M) solution of oxalic acid, accurately weigh 3.15 g of crystalline oxalic acid (formula: C₂H₂O₄·2H₂O). Dissolve the crystals completely in distilled water using a beaker, transfer the solution to a 250 ml volumetric flask, and add distilled water up to the mark. Stopper and mix thoroughly to ensure uniform concentration. Label and use this solution as required.
2. Which mistakes do students commonly make while preparing oxalic acid solutions, and how can these affect marks in the practical exam?
Common errors include:
- Incorrect weighing of oxalic acid crystals, leading to inaccurate concentration.
- Failure to transfer all residue from the weighing vessel and beaker, resulting in loss of material.
- Not rinsing the funnel, beaker, or watch glass—causing incomplete transfer.
- Improper meniscus reading while making up to the mark in the volumetric flask.
These mistakes can cause the prepared solution to deviate from the required molarity, potentially resulting in lost marks due to calculation or procedural errors during evaluation.
3. Explain why oxalic acid can be used as a primary standard in board practicals, and how this benefits students preparing for CBSE Class 12 Chemistry assessments.
Oxalic acid is used as a primary standard because it is highly pure, stable, and non-hygroscopic. Its chemical composition remains unchanged under laboratory conditions, enabling precise calculation of concentration. This ensures reliable preparation of standard solutions, making titration results accurate and supporting high-scoring answers in practical board assessments.
4. Describe the necessary safety precautions students must follow when handling oxalic acid during solution preparation in the Chemistry practical exam.
Essential precautions:
- Wear gloves and safety goggles to avoid direct skin and eye contact.
- Use a clean, dry watch glass and measuring apparatus for weighing and transferring.
- Do not inhale or ingest oxalic acid, as it is toxic and can cause health hazards.
- Handle with care to prevent spills, and clean any residual crystals thoroughly after transfer.
- Dispose of waste as per lab safety protocols.
5. How is the required mass of oxalic acid calculated for preparing solutions of different normalities or molarities in exam situations?
Calculate the required mass using formulas:
- Molarity (M): grams required = (Molarity × Molar mass × Volume in L)
- Normality (N): grams required = (Normality × Equivalent weight × Volume in L)
For oxalic acid (equivalent weight = 63 g, molar mass = 126 g): For a 0.1 M (M/10) 250 ml solution:
grams = 0.1 × 126 × 0.25 = 3.15 g. This method can be adjusted for other concentrations or volumes during exams.
6. In board practicals, why is a volumetric flask preferred over other lab glassware for preparing standard solutions?
A volumetric flask offers precise volume measurement due to its standardized calibration. This ensures that the prepared solution has an exact and reproducible volume, which is crucial for obtaining accurate and reliable results in titration and scoring full marks during practical assessments.
7. What procedural step is vital to ensure complete transfer of oxalic acid during solution preparation for practical exams?
After transferring oxalic acid from the weighing vessel or beaker, it is essential to rinse all apparatus (watch glass, beaker, funnel) with distilled water, ensuring all residual crystals are added to the volumetric flask. This guarantees that the solution’s concentration matches the calculation, which examiners expect for full credit.
8. How do examiners evaluate the accuracy of oxalic acid solution preparation during Class 12 Chemistry practicals?
Examiners assess:
- The accuracy of weighing the crystalline oxalic acid.
- The correctness and cleanliness of procedure and apparatus.
- Whether precautions were followed.
- The accuracy of making up volume in a volumetric flask.
- Recording and calculation skills in the observation table.
These criteria align with CBSE’s practical experiment marking scheme.
9. Why is heating sometimes necessary before titrating oxalic acid solutions in board practicals, and how can skipping this step impact results?
Heating the oxalic acid solution increases the reaction rate during titration with potassium permanganate (KMnO₄), ensuring faster and complete oxidation. Skipping heating can slow the reaction, leading to incomplete titration, error in endpoint detection, and reduced marks in the practical exam.
10. How does the accurate preparation of an oxalic acid solution demonstrate important chemical concepts relevant for high-order board questions?
Accurate solution preparation illustrates key concepts like mole concept, stoichiometry, primary standard substances, and the importance of precision in experimental chemistry. Mastery of these steps is often assessed in HOTS and long-answer board questions, reflecting a student’s deep understanding of both theory and laboratory practice.
