Lab S

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Chemistry

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Jan 9, 2024

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Lab S. Acids and Bases: Titrations Jayden Podmoroff 17122912 Partner: Miller Lab performed: Feb 15, 2019 Chem 123 L22 TA: Sydney Fearnley Lab Submitted: Feb 29, 2019 1

Introduction: The purpose of this experiment was to perform different acid-base titrations and observe the use of indicators in the titrations. Conducting this experiment will further the development skills in plotting graphical data and graphical interpretation. A titration is defined as a technique that uses a solution with a known concentration is used to find the unknown concentration of another solution. The titrations involved in Lab S are all acid-base titrations, where two both a strong (HCl) and weak (CH 3 COOH) acid are titrated with a basic solution (NaOH) of known concentration. The chemical reaction of the titration varies depending on whether the acid and base involved is strong or weak. The reaction for strong acid and strong base titrations are given in reaction (I) while the reaction for weak acid and strong base titrations are given in reaction (II). 1 The corresponding reactions are given below. 1 H 3 O + + OH -  2H 2 O (I) HA + OH -  A - + H 2 O (II) Once the acid has been fully neutralized by the base, the unknown concentration can be found using the total volume of base added and the balanced chemical equation reaction of the titration. The data obtained from a titration can be plotted as a graph into what is called a titration curve, where pH is plotted as a function of volume of titrant added. The equivalence point can be found using a titration curve graph by finding the average of the end point and start point, which is asked of Part A (intersecting points between tangent lines and slope of pH jump). 2 Part B seeks to find the endpoint of different titrations with the use of indicators. Indicators are weak acids or bases that are used to monitor the progress of a titration through colour change at certain pH 2

levels. The appropriate indicator must be used for the appropriate titration based off pH range in order to yield accurate results. The change in colour occurs when the indicator changes into its conjugate acid or base form through removal of a proton, using the equation (III) below. 3 HIn + OH -  H 2 O + In - (III) Colour I Colour II Procedure: The procedure of Lab S given by the First Year Chemistry Lab Manual 4 was followed as described below. Part A of Lab S required the use of a pH meter to find the equivalence point. First, the pH meter was calibrated by following steps described in the lab manual. A burette was attached to a retort stand and filled with an appropriate amount of standardized NaOH solution with concentration 0.105 M. 10.00 mL of the hydrochloric acid solution was pipetted into a 100 mL beaker along with about 20 mL of distilled water. The beaker was placed on a magnetic stirrer and a magnetic stirring flea was placed inside the beaker. The initial pH of the solution was recorded using the pH meter. The standardized NaOH solution was titrated very carefully with the HCl solution. The NaOH was added in small increments ranging from 1 mL to 0.1 mL and the reading from the pH meter was recorded after each corresponding addition. Smaller increments were used when finding the equivalence point of the titration and larger increments were used nearing the end of the titration. After completion of the titration, the exact same steps were repeated with the exception of using a acetic acid solution instead of an HCl solution. 5.00 mL of acetic acid was pipetted into a 100 mL beaker along with about 20 mL of distilled water to create the solution. 3

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