Buffer Preparation And Ph Measurement Using The Electrometric Method And Colorimetric Method.docx 1s56e

BUFFER PREPARATION AND PH MEASUREMENT USING THE ELECTROMETRIC METHOD AND COLORIMETRIC METHOD Arndrei John I. Cunanan, Angelica De La Torre, Maria Concepcion M. De Vera, Zandreah Regine T. Diaz, Lordjel Kin M. Eleda ABSTRACT An acetate buffer solution with a pH of approximately 5.00 was prepared from a solution that has an initial ph of 0.5 that is made by mixing 220 mL of distilled water with a 7.16 mL acetic acid. For the electrometric determination, a pH meter was used to determine the pH of the buffer solution and the chosen sample. Addition of NaOH and HCl was done to adjust the pH of the buffer solution towards the desired pH. On the other hand, acid-base indicators were used for the colorimetric determination of pH of both the buffer and the chosen sample. The change of color of the solutions was observed. It was later on found out that using a pH meter is a more accurate way of determining a pH of a solution rather than an indicator.

INTRODUCTION

HCl or 6.0 M NaOH while being monitored by the pH meter.

EXPERIMENTAL A. Compounds tested (or Samples used) For Buffer Solution: Acetic acid (CH3COOH) For Acid-base indicators: Thymol blue, Bromophenol blue, Bromocresol green, Bromocresol purple, Phenol red, Methyl red, Methyl orange, Phenolphthalein For Standard Reagent Preparation: Conc. HCl and Conc. NaOH Figure 1. pH meter

B. Procedure 1. Preparation of Reagents Prepare a 500 mL of the following aqueous solutions (6.0 M HCl and 6.0 M NaOH) and label the containers accordingly.

2. Buffers The buffer solution was prepared using the following guidelines: Table 1. Buffer solution used Volume (L) Concentration 0.250 L

4. Colorimetric Determination of pH a. Preparation of Color Standards using the Buffer Solution

Six test tubes were prepared and labeled with the pH of the buffer and acid-base indicator to be added. 5 ml of a buffer of a certain pH and 2 drops of an acid-base indicator was added into the test tubes. The mixture was shaken and the resulting color was noted. Buffer Solution

0.50 M

A volume of 220 mL of distilled water was added to 7.16 mL Acetic Acid (CH3COOH) into a 600 mL beaker then was transferred to volumetric flask. To make the buffer solution 250 mL in a volumetric flask, certain amounts of distilled water were added. The prepared solution was then transferred to a 500 mL amber bottle that was labeled properly.

3. Electrometric Determination of pH The pH meter was then calibrated at pH 4, 7 and 10. The pH of 20 ml portion of distilled water was measured and the [H+] was calculated. The pH of the buffer solution was adjusted to the desired pH by adding in portions of either 6.0 M

b. Determination of the pH of samples

Two drops of an acid-base indicator Acetate was added to 5 mL of distilled water. The mixture was shaken and the resulting color was noted. This procedure was repeated using each acid-base indicator.

RESULTS AND DISCUSSION 1. Electrometric Determination of pH In the experiment, from the initial pH of the buffer prepared (0.5), the desired pH of the acetate buffer which is 5.00 was reached through adding small amounts of 6.0 M HCl and 6.0 M NaOH. The calibrated pH meter showed accurate readings of the pH of the acetate buffer. It manifested sensitivity to a small amount of [H+] and [OH-] ions for it displayed fluctuations in readings with the slightest addition of 6.0 M HCl and 6.0 M NaOH. Therefore, the pH meter is

more accurate in reading pH levels compared to a pH paper.

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