Equivalent Weight Of Oxalic Acid: Calculation & Explanation

markdown # Equivalent Weight of Oxalic Acid: Calculation & Explanation Hello everyone! Today, we're going to tackle a very important concept in chemistry: the equivalent weight of oxalic acid. Many students find this topic a bit tricky, but don't worry! We'll break it down step-by-step to make sure you understand it completely. We'll go through the definition of equivalent weight, the formula for calculating it, and then apply that formula specifically to oxalic acid. So, let's dive in and get a clear understanding of this crucial concept. ## Correct Answer The equivalent weight of oxalic acid (H₂C₂O₄ · 2H₂O) is **63 g/equivalent**. ## Detailed Explanation Let's explore how we arrive at this answer. Understanding equivalent weight is essential in various chemical calculations, especially in titrations and redox reactions. To calculate the equivalent weight of oxalic acid, we need to understand a few key concepts first. ### Key Concepts 1. ***Molecular Weight:*** The molecular weight of a compound is the sum of the atomic weights of all the atoms in the molecule. For oxalic acid dihydrate (H₂C₂O₄ · 2H₂O), we need to consider the water molecules as well. 2. ***Basicity:*** The basicity of an acid is the number of replaceable hydrogen ions (H⁺) in one molecule of the acid. Oxalic acid is a *diprotic* acid, meaning it has two replaceable hydrogen ions. 3. ***Equivalent Weight:*** The equivalent weight of a substance is its molecular weight divided by its n-factor. The n-factor depends on the reaction the substance is undergoing. For acids, the n-factor is often the basicity. 4. ***Oxalic Acid:*** Oxalic acid, with the chemical formula H₂C₂O₄, is a dicarboxylic acid. This means it has two carboxyl groups (-COOH). In its hydrated form (H₂C₂O₄ · 2H₂O), it includes two water molecules. Now, let’s move step by step to calculate the equivalent weight of oxalic acid. **Step 1: Determine the Molecular Weight of Oxalic Acid Dihydrate (H₂C₂O₄ · 2H₂O)** To find the molecular weight, we add up the atomic weights of all the atoms in the formula: * Hydrogen (H): 1 amu * 4 = 4 amu * Carbon (C): 12 amu * 2 = 24 amu * Oxygen (O): 16 amu * 6 = 96 amu Adding these up: Molecular weight = (4 * 1) + (2 * 12) + (6 * 16) + (2 * 18) = 4 + 24 + 96 + 36 = 126 amu So, the molecular weight of anhydrous oxalic acid (H₂C₂O₄) is 90 amu. However, we're dealing with the dihydrate form (H₂C₂O₄ · 2H₂O), so we need to include the weight of two water molecules (2 * H₂O). * Molecular weight of water (H₂O) = (2 * 1) + 16 = 18 amu * Molecular weight of 2H₂O = 2 * 18 = 36 amu Adding this to the anhydrous form: Molecular weight of H₂C₂O₄ · 2H₂O = 90 + 36 = 126 amu Therefore, the molecular weight of oxalic acid dihydrate is 126 g/mol. **Step 2: Determine the Basicity (n-factor) of Oxalic Acid** Oxalic acid (H₂C₂O₄) is a *diprotic* acid. This means it can donate two protons (H⁺ ions) in a reaction. The two carboxylic acid groups (-COOH) each contribute one proton. Thus, the basicity or n-factor of oxalic acid is 2. In other words, it has two replaceable hydrogen ions. **Step 3: Calculate the Equivalent Weight** The formula for equivalent weight is: Equivalent Weight = (Molecular Weight) / (n-factor) Using the values we found: Equivalent Weight = 126 g/mol / 2 = 63 g/equivalent Therefore, the equivalent weight of oxalic acid dihydrate (H₂C₂O₄ · 2H₂O) is 63 g/equivalent. **Example to understand n-factor clearly:** For acids, the n-factor is the number of replaceable H+ ions. For bases, it is the number of replaceable OH- ions. In redox reactions, it is the number of electrons transferred per molecule. * For H₂SO₄, the n-factor is 2 because it can donate two H+ ions. * For HCl, the n-factor is 1 as it donates one H+ ion. * For NaOH, the n-factor is 1 because it has one replaceable OH- ion. ### Practical Importance of Equivalent Weight Understanding equivalent weight is extremely important in several contexts, including: * ***Titration:*** In titrations, particularly acid-base titrations, the concept of equivalent weight helps determine the amount of a substance needed to neutralize another. * ***Normality:*** Normality is a concentration unit defined as the number of equivalents of solute per liter of solution. Using equivalent weight makes normality calculations straightforward. * ***Stoichiometry:*** In stoichiometric calculations, equivalent weight helps in determining the combining ratios of reactants in a chemical reaction. * ***Redox Reactions:*** In redox reactions, equivalent weight is calculated based on the number of electrons transferred, making it vital for balancing redox equations. ### Common Mistakes to Avoid When Calculating Equivalent Weight * **Using the Wrong Molecular Weight:** Always make sure to use the correct molecular weight, especially for hydrated compounds. For oxalic acid, using the anhydrous form’s molecular weight (90 g/mol) instead of the dihydrate form (126 g/mol) will lead to an incorrect equivalent weight. * **Incorrect n-factor:** Determining the n-factor incorrectly is a common mistake. For acids, the n-factor is the basicity, which is the number of replaceable hydrogen ions. For oxalic acid, which is diprotic, the n-factor is 2. * **Not Considering Hydration:** For hydrated compounds like oxalic acid dihydrate, it’s essential to include the water molecules in the molecular weight calculation. Forgetting the water of hydration will give you a wrong molecular weight and, consequently, a wrong equivalent weight. * **Confusing with Molar Mass:** Equivalent weight is not the same as molar mass. Molar mass is the mass of one mole of a substance, while equivalent weight is the mass of a substance that will react with or replace one mole of hydrogen ions (for acids) or hydroxide ions (for bases) or one mole of electrons in a redox reaction. * **Misunderstanding the Reaction:** The n-factor can change based on the specific reaction. For instance, if oxalic acid only donates one proton in a particular reaction, the n-factor would be 1, not 2. Always consider the context of the reaction. ### Real-World Applications Oxalic acid and its equivalent weight have various applications in industries and laboratories. Here are a few: * ***Textile Industry:*** Oxalic acid is used as a bleaching agent in the textile industry. Understanding its equivalent weight helps in preparing the correct concentrations for bleaching solutions. * ***Leather Industry:*** It is also used in the leather industry for tanning processes. The equivalent weight helps in determining the appropriate amount of oxalic acid required for the tanning process. * ***Analytical Chemistry:*** Oxalic acid is a common reagent in analytical chemistry, especially in titrations. Knowing its equivalent weight is crucial for accurate titrations and quantitative analysis. * ***Rust Removal:*** Oxalic acid is effective in removing rust and stains. Its equivalent weight helps in preparing solutions of the right concentration for these applications. * ***Pharmaceutical Industry:*** In the pharmaceutical industry, oxalic acid is used in the synthesis of certain drugs. Understanding its chemical properties, including equivalent weight, is essential for safe and effective drug synthesis. ### A Deeper Dive into Titration and Equivalent Weight Titration is a common laboratory method used to determine the concentration of a solution. It involves the gradual addition of a solution of known concentration (the titrant) to a solution of unknown concentration (the analyte) until the reaction between them is complete. * **Acid-Base Titration:** In acid-base titrations, the equivalent weight of the acid and base plays a critical role. The endpoint of the titration is reached when the number of equivalents of the acid equals the number of equivalents of the base. * **Redox Titration:** In redox titrations, the equivalent weight is determined by the number of electrons transferred. For example, in the titration of oxalic acid with potassium permanganate (KMnO₄), the n-factor for oxalic acid is 2 because it loses two electrons when it is oxidized to carbon dioxide (CO₂). * **Normality and Titration Calculations:** The normality (N) of a solution is defined as the number of equivalents of solute per liter of solution. The relationship between normality, volume, and number of equivalents is given by: Equivalents = Normality * Volume In titration, at the equivalence point: (Equivalents of Acid) = (Equivalents of Base) (N₁ * V₁)Acid = (N₂ * V₂)Base Understanding equivalent weight and normality simplifies titration calculations and ensures accurate results. ### Importance of Hydration State in Calculations Always consider the hydration state of a compound when calculating its molecular and equivalent weights. Oxalic acid is commonly used in its dihydrated form (H₂C₂O₄ · 2H₂O). The water molecules contribute to the overall molecular weight, which affects the equivalent weight. If you use the molecular weight of anhydrous oxalic acid (H₂C₂O₄), your calculations will be incorrect. **Example illustrating the effect of hydration:** * **Using Anhydrous Oxalic Acid (H₂C₂O₄):** Molecular Weight = 90 g/mol n-factor = 2 Equivalent Weight = 90 / 2 = 45 g/equivalent * **Using Oxalic Acid Dihydrate (H₂C₂O₄ · 2H₂O):** Molecular Weight = 126 g/mol n-factor = 2 Equivalent Weight = 126 / 2 = 63 g/equivalent As you can see, using the correct form is critical for accurate calculations. ## Key Takeaways * The equivalent weight of oxalic acid dihydrate (H₂C₂O₄ · 2H₂O) is 63 g/equivalent. * The molecular weight of oxalic acid dihydrate is 126 g/mol. * Oxalic acid is a diprotic acid with a basicity (n-factor) of 2. * Equivalent weight is calculated by dividing the molecular weight by the n-factor. * Understanding equivalent weight is crucial for accurate calculations in titrations, stoichiometry, and redox reactions. * Always consider the hydration state of the compound when calculating its molecular and equivalent weights. I hope this detailed explanation clarifies the concept of equivalent weight of oxalic acid. If you have any more questions, feel free to ask!