Chemistry 1225 Lab Write-Up #13

Abstract

Introduction

Electrolysis is a method that is used to separate compounds by attracting ions in aqueous solutions to the opposite electrode. This means the electrode that is attached to the negative pole of the battery (supplies electrons) is called the cathode. The electrode attracted to the positive pole of the battery (accepts electrons) is called the anode. Electrodes that contain graphite are widely used – graphite is typically used because they are inert.

In order to successfully ionize, the aqueous electrolyte containing hydrogen and hydroxide ions as well as the solute compete with each other at the electrodes. The hydrogen atoms (H2) are reduced at the cathode whereas the oxygen atoms (O2) are oxidized at the anode. When there is an electric current running through an aqueous solution containing an electrolyte, water molecules separate into hydrogen and oxygen. Therefore, the reaction occurs as two distinct half reactions. As a result, each half reaction is accompanied by hydroxide (OH-) and Hydronium (H+) ions. The OH- ions will assemble at the cathode and cause the pH to increase. At the anode, H+ ions will gather and therefore cause the pH to decrease.

A universal indicator is a solution that undergoes several color changes over a wide range of pH values. The color is used to indicate pH directly. Universal indicators are usually mixtures of several indicators.

pH
Color
4
Red
5
Orange
6
Yellow
7
Green
8
Blue / Green
9
Dark Blue
10
Purple

Procedure

Part A: Universal Indicator and Sodium Sulfate

Begin by obtaining a petri dish. Separate the petri dish so you now have two halves in front of you. Pour approximately 5-10 mL of universal indicator to roughly 20-30 mL of sodium sulfate solution. Mix both of them thoroughly. Pour just enough of this solution into the petri dish in order to cover the bottom half of the dish.
Obtain pencil lead. Break the piece of lead in half. Attach one half of lead to one side of the petri dish with an alligator clip and attach the other half of lead to the opposite side with the other alligator clip. Without having the alligator tips submerged in the solution be sure both halves of the lead are submerged. Attach the 9V battery to the snaps that are