DETERMINACION DE SOLUBILIDAD

Laboratory Practice: Solubility of Benzoic Acid and Entropy of Dissolution

Introduction to the Laboratory Practice

• Laura Carolina Hernández introduces herself as a teacher in environmental engineering, presenting a laboratory practice on thermodynamics focused on the solubility of benzoic acid and entropy of dissolution.

• Emphasizes the importance of safety equipment in the lab, including lab coats, safety glasses, gloves, and masks.

Materials Required for the Experiment

• Lists materials needed: solid benzoic acid, sodium hydroxide (as base), phenolphthalein (indicator), 100 mL graduated cylinder, burette, stirrers, thermometer, pipette, universal support stand, 500 mL beaker with magnetic stirrer for water bath.

Procedure Overview

• Describes initial steps: weighing 1 gram of benzoic acid using an analytical balance and preparing a 20 mL aliquot of distilled water.

• Explains that solubility is the property allowing solutes to dissolve in solvents; it varies with temperature.

Conducting the Experiment

• Discusses heating solutions using a water bath to maintain constant temperature while dissolving benzoic acid.

• Advises on maintaining temperatures above room temperature (30°C to 50°C) to enhance solubility during titration.

Titration Process

• Instructs on filling the burette with sodium hydroxide solution ensuring no air bubbles are present before starting titration.

• Highlights adding phenolphthalein indicator which changes color based on pH levels during neutralization process.

Data Collection and Observations

• Stresses recording temperatures at which titration occurs along with volume consumed from the base for data analysis.

• Reminds not to forget adding indicator; suggests using 2 to 3 drops only. Ensures constant agitation throughout experiment for accurate results.

Titration Procedure and Key Concepts

Introduction to the Titration Process

• The transition of the indicator from transparent to pink should be subtle; a fuchsia color indicates overshooting the titration endpoint.

• The procedure begins with preparing benzoic acid, using a spatula and a watch glass for measurement.

Preparation Steps

• One gram of benzoic acid is dissolved in distilled water, followed by titration using a burette filled with sodium hydroxide.

• Solubility is defined as the ability of solutes to dissolve in solvents, which varies with temperature; heating is essential for maintaining consistent conditions.

Maintaining Temperature and Agitation

• A 500 ml beaker filled with water will serve as a water bath at an initial temperature of 45 degrees Celsius to ensure constant temperature during the experiment.

• Continuous agitation is necessary for homogeneity in the solution throughout the titration process.

Indicator Usage and Recommendations

• The octalene indicator changes color based on pH levels, transitioning from transparent to light pink; careful monitoring is crucial.

• Avoid air bubbles in the burette during filling, as they can affect volume readings. If bubbles are present, refill the burette.

Finalizing Measurements

• Aim for a very light pink hue; if it turns fuchsia, repeat the titration due to overshooting.

• Record final data including system temperature and volume of sodium hydroxide used at completion.

Practical Execution

• Ensure that when filling the burette, it’s done at eye level for accuracy. Any excess liquid must be removed by opening the valve.

• Confirm that meniscus aligns above the calibration mark before proceeding with further steps in preparation.

Solution Preparation Details

• Prepare benzoic acid solution carefully while ensuring all equipment (like pipettes and flasks) are clean and dry prior to use.

• Begin heating water before adding distilled water into benzoic acid mixture; maintain focus on achieving proper temperatures throughout.

Titration Process and Temperature Control

Heating the Solution

• The heating plate is set to 55 degrees Celsius, but the current temperature reads 40 degrees. The goal is to increase it to 45 degrees for optimal conditions.

• Adjustments are made to the heating ramp due to energy losses from the plate, which affects temperature readings. It's crucial to maintain a consistent temperature throughout the process.

Adding Indicator and Sodium Hydroxide

• Once the target temperature is reached, titration begins with the addition of an indicator (phenolphthalein). About 2-4 drops are sufficient for this step. Continuous agitation is necessary during this phase.

• Monitoring color changes in the solution is essential as sodium hydroxide (NaOH) is added; patience is required to avoid overshooting the endpoint of titration. The solution should transition from clear to a pale pink hue.

Achieving Endpoint of Titration

• The desired endpoint color should be a very light pink that remains stable for at least 30 seconds; any change indicates that too much NaOH has been added, surpassing neutralization point. This specific coloration signifies successful titration completion.

• Upon reaching this endpoint, it's important to record both the volume of NaOH used (approximately 23.9 mL) and ensure significant figures are noted accurately when measuring liquid levels using meniscus readings.

Concentration Measurement and Future Steps

• Before concluding, measure the concentration of NaOH used in titration (0.10 N), as this data will be vital for subsequent calculations related to acid-base reactions performed during practice sessions.

• Future experiments will involve preparing solutions at varying temperatures (40°C, 35°C, and downwards) with expectations that lower temperatures will require less NaOH for neutralization due to decreased solubility of acids in cooler conditions. This aims at understanding how temperature influences titration outcomes effectively.