NOTE: The chart "Common chemicals and their type of electroltyte.pdf" (which you need to study for Quiz #1 to be given in lecture on Tuesday, February 10) is available for download at the bottom of this page as well as at the bottom of the CHEM 150 Lecture Handout page.
This web page is being used for "Flipped Learning" in CHEM 150. The page is lengthy, and eventually I plan to split it into sub-pages in the future. For now, please scroll down as required to reach the material that you are interested in. Thank you!
According to one popular web site (www.flippedlearning.org): "Flipped Learning occurs when direct instruction is moved from the group teaching space to the individual learning environment. Class time is then used for higher order, active problem solving by students and one-to-one or small group interactions with the teacher. Educators are embracing Flipped Learning in elementary and secondary schools for all subjects."
Flipped Learning has its advantages and its disadvantages. At one extreme, students no longer any receive in-class lectures, and they become personally responsible for looking at all of the lecture videos on their own time. If students do not have the time to look at these videos, obviously they will not learn the material, and the end result is that they will learn less, not more. At the other extreme, if students become actively involved in watching the videos outside of class, they will be familiar with the topics much sooner. The teacher or professor will then be able to use class time more efficiently by answering student questions, go over homework assignments, have class discussions relating to the course material, etc. There is a wide variation in the meaning and application of the Flipped Learning concept in different schools throughout the USA and other countries.
I am using Flipped Learning this semester to help my students learn and understand a variety of topics that are covered in CHEM 150. To access the videos relating to each topic, please scroll down in this page until you reach that topic. In the near future, this page will be broken down into sub-pages to make it much easier for you to locate these videos.
I. TYPES OF ELECTROLYTES
Please begin by watching these YouTube videos, and then continue reading underneath. You will be doing this conductivity experiment with a variety of different soluble compounds (electrolytes) in the CHEM 150L lab later this semester.
The Basics of Electrolytes
Types of Electrolytes
Conductivity of Acetic Acid (before and after adding water)
Important note: The person who prepared the above acetic acid video incorrectly stated that acetic acid is a strong electrolyte after a large amount of water has been added. This statement is not true! Although significantly more ions are formed as more and more water is added, acetic acid is still classified only as a weak electrolyte because it dissociates only partially into ions in an aqueous (water) solution.
Strong Acids and Weak Acids
Summary of information that you need to know:
1. Strong electrolytes dissociate completely into their constituent ions when they are dissolved in water. The solution that results contains a large concentration of ions, and it conducts electricity very well (as is shown by the lamp glowing brightly). There is NO chemical equilibrium, because there is a virtually complete dissociation reaction from left to right.
a. Strong acids such as hydrochloric acid, HCl(aq)
Note that pure HCl (hydrogen chloride) is a gas that does not dissociate into any ions at all. Ions are formed only after this gas is dissolved in water. We called the resulting solution "hydrochloric acid" but you need to remember that the solution contains only hydronium ions (H3O+) and chloride ions (Cl-).
b. Strong bases such as sodium hydroxide, NaOH(aq)
c. Soluble salts such as sodium chloride, NaCl(aq)
2. Weak electrolytes dissociate only partially into their constituent ions when they are dissolved in water. The solution that results contains a small concentration of ions, enough to conduct electricity only poorly (as is shown by the lamp glowing dimly). You can always write an equilibrium constant expression (Ka, Kb, or Kw, as appropriate) for the dissociation reaction, because the chemical dissociate only partially from left to right.
a. Weak acids such as acetic acid, HC2H3O2(aq)
b. Weak bases such as aqueous ammonia, NH3(aq)
c. Water, H2O(l)
Note that pure acetic acid (a liquid often called "glacial acetic acid) does not dissociate into any ions at all. It is only when water is added to this glacial acetic acid that ions are produced, and the solution conducts electricity only poorly.
The concentration of ions in pure deionized water is so small that the lamp does not glow at all. This observation does not change the fact that water is a (very) weak electrolyte. The testing equipment (the lamp and the associated electrical circuit) is not sensitive enough to measure the tiny amount of current that is actually flowing throughout the circuit when deionized water is tested.
3. Non-electrolytes do not dissociate into their constituent ions at all when they are dissolved in water. The solution that results contains no ions, and the lamp does not glow at all. There is NO chemical equilibrium because the non-electrolyte remains in molecular form, and does not dissociate into its ions at all.
a. Sugar (sucrose), C12H22O11(aq)
b. Ethyl alcohol, C2H5OH(aq)
II. MOLECULAR ("FORMULA UNIT"), TOTAL IONIC, AND NET IONIC EQUATIONS
A good way to introduce this topic is to consider how these three types of reactions differ when we write chemical equations for reactions in which a solid "insoluble" precipitate is formed when two different clear solutions are mixed together. A simple precipitation reaction is shown in the following YouTube video:
An example of a precipitation reaction
Solubility charts (such as Table 17.3 that follows) enable you to determine which common ionic compounds do, and do not, readily dissolve in water. You do not need to memorize the chart!
There are many good YouTube videos that explain the differences between: (1) molecular (sometimes called "formula unit") equations, (2) total ionic (sometimes called "ionic") equations, and (3) net ionic equations. I recommend that you watch each of the following three videos (in turn) now. These videos discuss several precipitation reactions of varying difficulty. Please pay very careful attention to the subscripts, charges, and coefficients of the ions in the equations that will be written.
In lecture, we will discuss (at the very end of Handout #1) how this concept is extended to acid-base neutralization reactions. Basically, you never split up (into its constituent ions) either a weak acid (such as acetic acid, formic acid, hydrocyanic acid, carbonic acid, or phosphoric acid), a weak base (such as aqueous ammonia), or water when you write these types of ionic reactions for acid-base neutralization reactions.
III. THERMOCHEMISTRY - HOW TO CALCULATE HEATS OF FORMATION (Handout #4)
The first page of handout #4 (writing the equations relating to standard heats of formation and bond energies) will be discussed in lecture. Please view the following videos that relate to the rest of Handout #4 (three ways of calculating heats of reactions using different approaches).
Method #1 - Calculating heats of reaction by combining thermochemical equations (Hess' Law)
Method #2 - Using standard molar enthalpies of formation (standard heats of formation)
This video features "Dr. Fus" who has completely flipped his General Chemistry courses (see above).
Method #3 - Using tabulated average bond energies
Alex Tah has some good bond energy videos on YouTube. Because he takes the time to explain things slowly and clearly,
these videos are a bit longer than those shown above, but I think it will be well worth your time to look at both of them.
IV. CHEMICAL KINETICS (Rates of chemical reactions - handout #5)
Introduction: how to speed up chemical reactions (and get a date)
Collision Theory (IsaacsTEACH - 11.1)
Potential Energy Diagrams (IsaacsTEACH - 11.2)
Rate of Reaction and Rate Laws (IsaacsTEACH - 11.3)
Factors that affect Reaction Rate (IsaacsTEACH - 11.4)
Reaction Mechanisms and Rate Limiting Step (IsaacsTEACH - 11.5)
Nuclear Half Life: Calculations (Tyler DeWitt)
For more complicated half-life calculations, please use the equations discussed in the lecture handout.
Salman Khan has somewhat different teaching techniques. For example, here is one of his videos.
Introduction to Chemical Kinetics
Thank you for watching the chemical kinetics videos!!
This ends the Flipped Learning videos dealing with the topics listed at the top of this web page. Please let me know whether or not you found these videos useful, and let me have your suggestions and comments for possible changes in the future. Thank you.