Upon completion of this experiment, students will:
(CLO1). Explain basic chemical concepts related to chemical changes, energy, and properties of matter.
(MLO) Describe and predict properties of electrolytes to categorize compounds as nonelectrolytes, weak electrolytes or strong electrolytes.
Use methods and tools to measure conductivity of solutions and during titrations
Experiment 10 discusses the nature and properties of matter in terms of conductivity, conductor or insulator.
The assignments that must be completed are:
Complete the pre laboratory quiz in Canvas before coming to the class meeting.
Use the conductivity probes and MicroLab system to make observations and record the appropriate data for each part of the laboratory report. Complete all questions in the Laboratory Report.
Electrical charge is able to move through substances when electrons or ionic charge is mobile and flows through the substance. Metallic substances have delocalized electrons that are able to move freely through the materials allowing a current to flow. Substances that conduct electricity freely are called conductors, while substances that impede the flow of electrons are called insulators. Substances with covalent bonds generally have electrons that are localized in the bond and therefore are not free to flow.
For substances that have ionic bonds, the electrons are localized while the substance is in the solid state. The solid state ionic compounds are non conductors; however, when the ionic substance is dissolved in water, the ionic compound dissociates into positively and negatively charged species. These aqueous solutions contain ions that are hydrated and stabilized by the polarity of the water molecule, which allows the ionic charge to be freely mobile in the water solution. This freely mobile ionic charge are potential conductors of electricity and are called electrolytic solutions or electrolytes.
Some substances dissociate completely and are very good conductors while some substances although they dissolve well do not dissociate completely. These substances have fewer ionic charge and therefore are not able to conduct electricity as well. These substances are called weak electrolytes. Many of these substances have strictly covalent type bonding but are also considered to be acidic or basic in nature. Acids are most easily identified by the presence of a hydrogen atom that can be dissociated. These hydrogen ions are often written in the first position, such as HNO3, HC2H3O2. However, even when we can identify an acid, some are strong acids, which dissociate completely; while others are weak acids, which dissociate partially.
The easiest way to predict conductivity is by looking at the partners in the bond:
metallic bonds which include pure metals and alloys are good or strong conductors
ionic bonds which include a metallic atom bonded to a non metallic atom or a polyatomic ion are non conductors in the solid state but if soluble strong electrolytes in solution
covalent bonds which include a non metallic atom bonded to a nonmetallic atom are generally non electrolytes
acids and bases when in solution can either be weak or strong electrolytes depending upon their ability to dissociate in solution.
https://youtu.be/0cPFx0wFuVs
Tyler DeWitt - We'll look at what happens when you dissolve ionic and covalent compounds in water. Ionic compounds break apart into the ions that make them up, a process called dissociation, while covalent compounds only break into the molecules, not the individual atoms.
BerkeleyChemDemos
This demonstration shows the conductivity of solids and aqueous solutions of the solids.
There is no required pre laboratory writing assignment.
The pre laboratory problems are questions about the laboratory assignment, background, definitions or procedure and calculations. These problems should be completed BEFORE coming to the class where the assignment will be discussed.
The pre laboratory problems for this experiment should be completed as a quiz in Canvas.
The laboratory report of the assignment contains questions, data collection, calculation and reporting of results.
A Conductivity tester will be provided to each group, who will determine the conductivity of each sample provided. Make sure you rinse and dry the conductivity tester's probe wires between each sample to minimize contamination of the samples use the conductivity tester to test the conductance of each sample.
To measure the conductivity of several liquids and solutions, we will use the MicroLab system and a conductivity probe. The system set up and calibration of the conductivity probe is described in this video.
MicroLab will be used to collect the data for this experiment. The directions for using this program is available at
https://drive.google.com/open?id=1msCKCy0Y5CNKjrLCZj8S4w633NE0H7SZXstbaV10RkY
Set up the MicroLab and Conductivity probe and then calibrate the probe. The document shows how to calibrate the probe and measure the conductivity of the samples.
We can use standardized solutions to calibrate the conductivity probe and then measure the conductance of each of the solutions.
Electrolytes
We will prepare serial dilutions of two solutions and test the solution's conductance. Use the conductivity probe to measure the conductance of acetic acid and NaCl solution at various concentration. We will graph the concentration of the solution versus the conductance.
We will set up the titration of two different reactions. You need to be able to predict the products of the reaction of these two solutions. Identify whether the products are strong, weak or non electrolytes, soluble or insoluble compounds. The instructor may set up one computer for each of these reactions to allow the student to graph conductivity as a result of time and added substrate. These involve changes occurring to the conductivity of the original sample. Net ionic reactions will help explain the change in conductivity if the products of the reaction are understood to be either strong electrolytes, weak electrolytes or non electrolytes. A graph of the conductance versus the volume of the titrant added will be created.
In a titration, when two separate aqueous ionic compounds are mixed the ions may interact. The ionic compounds in a double replacement reaction switches partners. If these partners result in an ionic compound that remains dissolved, then the products of the mixture are strong electrolytes and the reaction is said to have no apparent reaction. When the product of the double replacement reaction is a precipitate or solid, a weak electrolyte or acid, a non electrolyte or a gaseous substance, the removal of the freely dissociated ions can cause a decrease in the conductivity of the solutions. Sometimes the reaction results in the formation of a strong electrolyte from weak electrolytes.
There is no post laboratory problems and conclusion paragraph for this laboratory assignment.