### Introduction

In this experiment, you will study the electrical conductivity of water and various water solutions. A solution can contain molecules, ions, or both. Some substances, such as sucrose (C12H22O11) and glucose (C6H12O6), dissolve to give a solution containing mostly molecules. An equation representing the dissolving of sucrose (table sugar) in water is:

${{\text{C}}_{{\text{12}}}}{{\text{H}}_{{\text{22}}}}{{\text{O}}_{{\text{11}}}}{\text{(s)}} \leftrightarrow {{\text{C}}_{{\text{12}}}}{{\text{H}}_{{\text{22}}}}{{\text{O}}_{{\text{11}}}}{\text{(aq)}}$

where (s) refers to a solid substance and (aq) refers to a substance dissolved in water. Other substances, such as calcium chloride (CaCl2), dissolve in water to produce a solution containing mostly ions. An equation is:

${\text{CaC}}{{\text{l}}_{\text{2}}}{\text{(s) }} \leftrightarrow {\text{ C}}{{\text{a}}^{{\text{2 + }}}}{\text{(aq) + 2C}}{{\text{l}}^{\text{ - }}}{\text{(aq)}}$

Calcium ions are necessary for muscle contraction, mitochondrial activity, bone formation, and many other metabolic processes. Organisms may obtain minerals such as calcium from their water supply, since ions dissolve in water.

You will determine conductivity of the solutions using a computer-interfaced Conductivity Probe. The unit of conductivity in this experiment is microsiemens per centimeter, or µS/cm.

### Objectives

In this experiment, you will

• Write equations for the dissolving of substances in water.
• Use a Conductivity Probe to test the electrical conductivity of solutions.
• Determine whether molecules or ions are responsible for electrical conductivity of solutions.