Neutralization (Acid-Base) Titration: Determining Concentration of HCl

Purpose and Principle of HCl Neutralization Titration

The primary objective of this laboratory exercise is to determine the unknown molarity ($M$) and mass concentration ($g/L$) of a Hydrochloric acid ($HCl$) solution. This is achieved through the process of titration, involving the reaction of the acid against a standard solution of sodium carbonate ($Na_2CO_3$), which has a known concentration of $0.05\,M$. The chemical principle underlying this experiment is a neutralization reaction. Based on the provided material, the specific reaction occurring during the titration is represented by the equation: $HCl + Na_2CO_3 \rightarrow NaHCO_3 + NaCl$. In this reaction, the titration identifies the point at which the Hydrochloric acid has reacted sufficiently with the sodium carbonate to reach a specific chemical endpoint, facilitated by the use of an indicator.

Laboratory Requirements and Apparatus

To perform this titration accurately, several specific pieces of glassware and chemical reagents are required. The chemical reagents include Hydrochloric acid ($HCl$) of unknown concentration, sodium carbonate ($Na_2CO_3$) at a standard concentration of $0.05\,M$, distilled water for cleaning and dilution, and Phenolphthalein ($ph.ph$) which serves as the visual indicator. The laboratory apparatus consists of a burette and a burette stand with a clamp for controlled delivery of the acid. A volumetric pipette ($10\,ml$) and a pipette filler are used to measure the base. The reaction takes place in a conical flask, which is placed on a white tile to better observe the color change of the indicator. Additional equipment includes a funnel for filling the burette, beakers for holding solutions, a volumetric flask, a dropping bottle for the indicator, and a wash bottle containing distilled water for rinsing.

Detailed Experimental Procedure

The titration process begins by using a volumetric pipette to accurately measure and transfer a specific volume, exactly $10\,ml$, of the $0.05\,M$ sodium carbonate ($Na_2CO_3$) solution into a clean conical flask. Following this, a few drops of the Phenolphthalein ($ph.ph$) indicator are added to the flask; the solution will typically exhibit a red-pink color in this basic environment. The burette is then filled with the Hydrochloric acid ($HCl$) of unknown concentration, ensuring the meniscus is properly aligned with the initial graduation mark. The titration is performed by slowly adding the $HCl$ from the burette into the conical flask while constantly shaking or swirling the flask to ensure thorough mixing. This addition continues until the indicator undergoes a distinct color change from red-pink to a near colorless state. This transition signifies the endpoint of the titration. At this moment, the flow from the burette is stopped immediately, and the final volume of $HCl$ used is recorded. To ensure accuracy and precision, the titration is repeated multiple times until concordant results are achieved, defined as readings where the average volume difference does not exceed $0.2\,cm^3$.

Results, Observations, and Data Collection

Data collection is organized into a systematic results table to track the titration progress across multiple trials. For each experiment number ($No.\text{ of Ex.}$), the following data points must be recorded: the Initial Burette Reading ($ml$), the Final Burette Reading ($ml$), and the total Volume used ($ml$), which is calculated as the difference between the final and initial readings. Examples provided in the documentation show specific volume readings such as $19.62\,cm^3$, $19.50\,cm^3$, and $19.42\,cm^3$. Once multiple trials are completed, the average volume of $HCl$ consumed is calculated using the concordant values to used in the final molarity calculations.

Quantitative Analysis and Calculations

The calculation phase uses the titration formula to derive the molarity of the unknown acid. The relationship is defined by the equation: $\frac{M_1 \times V_1}{x} = rac{M_2 \times V_2}{y}$. In this context, $M_1$ represents the molarity of the Hydrochloric acid ($M$), $V_1$ is the volume of Hydrochloric acid used from the burette ($ml$), $M_2$ is the molarity of the Sodium carbonate ($0.05\,M$), and $V_2$ is the volume of Sodium carbonate in the flask ($10\,ml$). According to the reaction stoichiometry provided where the molar ratio is $1:1$ for this specific stage of neutralization, the formula simplifies to: $M_1 \times V_1 = 0.05 \times 10$. Solving for the molarity of the acid gives: $M_1 = \frac{0.05 \times 10}{V_1}$. After determining the molarity, the mass concentration in grams per liter can be calculated using the formula: $\text{Concentration of HCL } (g/L) = Molarity \times Molecular \text{ weight}$.