During each unit covered, I hand out a list of objectives to my students. For the teacher, it acts as a check-list to make sure each topic is taught before moving on to others. For the student, it helps them to prepare for tests and quizzes and they could ask questions about topics they were unsure about. It's up to the teacher (you) to edit accordingly-- and you can announce to your students if you want to eliminate an objective. Just let them know! They'll appreciate that!
Here's a sample list using the topics from today's blog post:
Unit II Objectives: Isotopes and Related Topics
(Chapters 3 & 4)
1. Define isotopes and atomic mass; calculate average isotopic mass from percent abundance data; report atoms and ions using symbol notation.
2. Find the percentage composition of a given formula; use percentage composition to determine the formula of an unknown sample; find empirical and molecular formulas.
3. Use facts and concepts presented in Chapters 3 & 4. (Be a careful reader!)
This last objective is a "cover all" objective that makes any topic addressed in the textbook chapters listed fair for quiz/test questions. I found it really useful when designing a quiz or test to make sure that each topic was addressed.
Right now, I won't be listing the objectives on my blog posts -- but it may show up in the future!
I think I've defined isotope before, but it is an element with different atomic mass due to different numbers of neutrons. A classic example is carbon-12 and carbon-14. The number provided is the mass number, so the number of neutrons could be calculated easily. (mass number - atomic number (# protons) = # of neutrons)
A very typical application is to calculate the weighted average based on the percent abundance of the isotope on Earth. For example, chlorine-35 has a percent abundance of 75.53% and chlorine-37 has a percent abundance of 24.47%.
To calculate the weighted average based on percent abundance:
1) Change the percent values to decimals by dividing by 100.
chlorine-35 = 0.7553 chlorine-37 = 0.2447
2) Multiple each mass number by the percent value in decimal form.
35 x 0.7553 =26.4355 37 x 0.2447 = 9.0539
3) Add the values together to get the weighted average isotopic mass.
26.4355 + 9.0539 =35.4894
Symbol notation reports the mass number as a superscript and the atomic number as a subscript. It's just a part of the language of chemistry. I've included it before, but just in case you need a reminder:
Calculating percent composition can be accomplished with the Periodic Table or with laboratory values.
Here's one percent composition worksheet using Periodic Table values:
A typical question would be to take the percent composition values and determine the empirical and molecular formulae of the compound. Here is one explanation:
Here's a worksheet and answers:
I like how the answers in the key are set up, to aid in converting to moles.
I've shared the composition of magnesium & oxygen lab previously -- it can also be used as an example of percent composition and empirical formula.
Here's a very simple lab:
Here is a longer version, but very useful:
I found some food-related labs determining the percent composition of bubble gum or Oreos -- since I don't want to encourage eating in the chemistry lab (safety first!), I have not included them here. Even if you tell your students not to eat in the lab, and remind them for this lab, there is at least one student who probably will sample the lab materials.
If you want to move to an alternate location, such as a consumer science kitchen, then this type of lab could work!
This lab is interesting as well:
Notice that I have addressed topics in each of objectives #1 & #2 -- the objective list is very useful, and your students appreciate it. They may start asking for it! Now, I have combined a list of smaller objectives together for each numbered item -- if every item was included by itself, it would be a very long list!
*I'd love to hear from you -- tell me about your lab experiences, ask your questions, or share your ideas for other topics for this blog!
For other lab ideas, check out my lab book "Chemistry on a Budget" at amazon.com:
Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
Have a good rest of the week!