INTRODUCTION
Many doctors and coaches recommend staying hydrated after exercising by drinking sports drinks containing electrolytes. Electrolytes are essential in the proper functioning of muscles and the nervous system, and losing too many electrolytes through sweating can cause cramps and headaches. So, what are electrolytes?
THEORY
DISSOCIATION
Many ionic compounds dissolve easily in water, forming ionic solutions. When they dissolve, the compounds break up into their individual ions, a process called dissociation.
For example, when table salt is dissolved in water, the sodium chloride breaks up into sodium ions and chloride ions. We can write the dissociation in the form of an equation:
NaCl
(𝑠)
→ Na
+
(𝑎𝑞)
+ Cl
−
(𝑎𝑞)
For every one molecule of solid (s) sodium chloride added to the water, two ions (one sodium ion and one chloride ion) can be found dissolved in the water (aq).
WEAK AND STRONG ELECTROLYTES
Ionic compounds that break up completely into their individual ions are called strong electrolytes. There are also ionic compounds that only partially break up into ions, which are called weak electrolytes.
One example of a weak electrolyte is acetic acid, H(CH
3
COO) , the acid in vinegar. When acetic acid is added to water, only some of the molecules break up into ions, and the rest remain joined together. The dissociation equation for acetic acid looks like:
H(CH
3
COO) ⇌ H
+
+ (CH
3
COO)
−
Notice that we use a double-headed arrow to describe how weak electrolytes dissociate.
CONDUCTIVITY
Ionic solutions are a good conductor of electricity. If we place two ends of an open circuit into a beaker containing salt water, electrons can readily flow from one electrode to the other through the ionic solution, closing the circuit. If more ions are added to the solution, the solution becomes a better conductor. If the compound doesn’t break into ions, the solution will be a poor conductor. Conductivity is measured in the units microsiemen per centimeter, or µS/cm.
In this lab, we will be using a special meter that can measure the conductivity of a solution. The probe contains an open circuit and a voltage meter.

LAB PROCEDURE
HYPOTHESIS
Molecules of ionic compounds break apart into a specific number of ions when they are added to water. By measuring how well the ionic solution conducts electricity, the number of ions in the solution can be found.
MATERIALS
 Computer with LoggerPro
 LabPro
 Conductivity probe
 Distilled water wash bottle
 250 mL flask
 Paper towels
 Equipment stand and clamp
 Vials of solutions o Sodium chloride o Calcium chloride o Aluminum chloride o Acetic acid o Hydrochloric acid o Tap water o Distilled water o Methanol
SAFETY PROCEDURES
 Acids are caustic. Avoid contact with eyes, skin and clothing. Wear goggles.
 Make sure cables are placed safely around the work space.
 Do not taste any of the chemicals.
PROCEDURE
1.
Connect the LabPro and conductivity probe to the computer. Make sure the switch on the conductivity probe is set to the “0-20000 μS/cm” setting. (If the label next to the switch is missing, make sure the switch is flipped in the direction of the “Conductivity Probe” label.) Start LoggerPro.
2.
Take vials of the first three solutions in the Materials list. For each solution, a.
Write the dissociation equation for the salt in the solution. Record how many ions will be formed when the salt dissociates. b.
Dip the conductivity probe into the solution vial so that the hole in the probe is completely covered. Swirl the vial around slightly and wait for the conductivity value to stabilize. c.
Clean the conductivity probe by placing it inside the 250 mL flask and rinsing it off with the distilled water wash bottle, then drying the outside of the probe with the paper towels. It isn’t necessary to dry inside the probe.
3.
Take vials of the two acids in the Materials list. For each solution, measure and record the conductivity as you did in Step 2. State if you think the acid is a strong electrolyte or a weak electrolyte.

4.
Take vials of the remaining three solutions. For each solution, measure and record the conductivity as you did in Step 2. State if you think the acid is an ionic solution or not.
DATA
Salt
Sodium chloride
Dissociation # of ions Conductivity
Calcium chloride
Aluminum chloride
Acid
Acetic acid
Hydrochloric acid
Conductivity Strong/weak?
Solution
Tap water
Distilled water
Methanol in water
Conductivity Ionic/non-ionic?