AP Chemistry Update

Today in class students (hopefully) increased their understanding of Chapter 4 material. The answers to Example #11 and Example #12 from the chapter 4 review guide were discussed. You can watch the PowerPoint Notes by clicking here. Just fast forward to the end to see Examples #11 and #12. Then we moved on to a discussion of Section 4.4 in the textbook (Oxidation-Reduction Reactions). Here are some important points about oxidation numbers:

• The oxidation number of an element in its elemental state is zero
• The oxidation number for a monoatomic ion is simply the charge on the ion
• The O.N. for alkali metals in compounds is +1
• The O.N. for alkaline earth metals in compounds is +2
• The O.N. for fluorine in compounds is -1
• The O.N. for oxygen in compounds is usually -2 (except peroxides or OF₂)
• The O.N. for hydrogen in compounds is usually +1 (except metal hydrides)
• In a binary covalent compound, the element that is more electronegative will have an O.N. equal to the charge it normally forms as a monoatomic ion
• The sum of the O.N. values is zero in a neutral chemical formula
• In a polyatomic ion, the sum of the O.N. values is equal to the charge on the ion

Now that you understand oxidation numbers, here is a procedure to help you balance a half-reaction:

• Step 1 = Balance the atoms of the element that is being oxidized or reduced
• Step 2 = Use electrons to balance the change in oxidation number ("OIL RIG" will remind you that oxidation is the loss of e^– and reduction is the gain of e^–)
• Step 3 = Use H⁺ ions (or OH^– ions) to balance the overall charge on both sides
• Step 4 = Use H₂O molecules to balance the H atoms and the O atoms

We did not get a chance to go over all of the homework problems in class today. I'll be talking more about that on Monday. The homework for Monday is to do the AP Multiple Choice Questions related to Chapter 4, which can be found here.

E-mail me with any questions. Have a good weekend.

AP Chemistry Update

The Homework for Friday is to answer questions 41-50 at the end of Chapter 4 from your textbook.

AP Chemistry Update

Today students learned more information about acid-base reactions. The following points were very important for writing net ionic equations:

• Strong acids (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₃, HClO₄) should be written as H⁺
• Weak acids (HF, HC₂H₃O₂, HNO₂, HCHO₂, etc.) should be written as one formula, whatever its chemical formula happens to be
• Strong bases (NaOH, KOH, Ca(OH)₂, etc.) should be written as OH^–
• Weak bases (NH₃, CH₃NH₂, etc.) that are either ammonia or an amine should be written as one formula, whatever its chemical formula happens to be
• Net ionic equations should be balanced with respect to atom count and overall charge

If you are doing stoichiometry calculations related to acid-base reactions, it's a very good idea to start by writing the molecular equation. This will help you see a complete picture of what is going on in solution. If you only look at the net ionic equation, you might not see the correct molar ratio between two reacting species.

Consider the example above, based on problem #31 from the textbook. Barium hydroxide, Ba(OH)₂, reacts with nitric acid, HNO₃. The molecular equation shows you the 2-to-1 molar ratio between nitric acid and barium hydroxide. You need to use this ratio in your calculation. If you had only written the net ionic equation, you might have missed this point. The net ionic equation shows a 1-to-1 ratio between H⁺ ions and OH^– ions.

Answers to the Chapter 4 homework problems have been posted here. The homework for Wednesday is to answer the Pre-Lab Questions for the titration lab. E-mail me if you have questions.

AP Chemistry Update

Today students learned about some of the properties of acids and bases. Acids can be classified as either strong or weak. Strong acids are completely dissociated into ions. Weak acids are only partially dissociated into ions. In the pictures below, hydrochloric acid (HCl) is a strong acid that is completely dissociated into ions, whereas hydrofluoric acid (HF) is a weak acid that is only partially dissociated.

Bases can also be classified as strong or weak. Strong bases are typically ionic compounds that contain hydroxide (OH^-) ions. A weak base is a molecule or ion that accepts H⁺. One example of a weak base is ammonia (NH₃).

When acids and bases react together, the acid loses H⁺ and the base gains H⁺. Acid-base reactions can be written in the form of net ionic equations. You have already had some practice with writing net ionic equations for precipitation reactions. You will need to practice writing net ionic equations for acid-base reactions. This will require you to know if an acid or a base is strong or weak. Therefore, just like you had memorized solubility rules, you should memorize the strong acids (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₃, and HClO₄).

The PowerPoint Notes for Chapter 4 have been updated to include Example #10 from your Chapter 4 Review Guide, which I discussed at the end of class today. This problem shows you four examples of net ionic equations.

Your homework for Monday is to answer the following questions from Chapter 4 in your textbook: 21 - 32 (on page 97).

E-mail me if you have questions. 

AP Chemistry Update

Today students reviewed their Chapter 4 homework in a way that encouraged collaboration and discussion in small groups. After class discussion, they turned in a worksheet that contained their answers to selected homework problems. Students also did a lab experiment today that was designed to help them strengthen their understanding of the solubility rules. Students mixed various solutions together and observed whether or not a precipitate would form. The homework for Friday is to write the net ionic equations for the precipitation reactions that occurred in the lab. A copy of the lab activity can be found here. Students should read ahead in Chapter 4 and be prepared to discuss acids and bases (Section 4.3).

AP Chemistry Chapter 4

If you missed class today, here is a summary of what we did:

Handouts for Chapter 4 were given to students. You can get your copy of this handout by clicking here.

We discussed the information in Sections 4.1 and 4.2. You can watch this PowerPoint slide show to follow along with the example problems in the Chapter 4 Review Guide.

The chapter 4 homework (which should be ready to turn in for a grade on Wednesday) are the following problems from pages 96-97 in your textbook:

1, 5(a) & (d), 7, 11, 13, 17

Unit 2 Test Coming Soon!

This week in Advanced Chemistry:

MONDAY
We finished up our laboratory discussion of Physical and Chemical Changes. We reviewed SOL Questions and did a lab on separation techniques. These included chromatography, filtration, distillation, and electrolysis.
TUESDAY
We discussed the separation techniques lab and students took notes on matter. Separation of mixtures can be done with a physical change. Decomposition of compounds can be done with a chemical change. Elements can't be separated by physical or chemical changes.
WEDNESDAY = We reviewed homework and students took a quiz on matter.
THURSDAY = We discussed the process of writing chemical equations and did a lab involving baking soda and vinegar.
FRIDAY = We discussed the law of conservation of mass and did a few example problems involving percent composition.

The unit 2 test is scheduled for Tuesday. The homework for this weekend is to do the Unit 2 Practice Test.

In AP Chemistry, we did a lab on Monday involving the empirical formula of hydrates. On Wednesday we reviewed a Chapter 3 practice test. On Friday we had a demo of the formation of tin oxide, and wrapped up Chapter 3. Students were given a take-home test for Chapter 3. This test is due on Monday morning when class begins

AP CHEMISTRY - CHAPTER 3 PREP

Chapter 3 Extra Practice

Chapter 3 Extra Practice - Answers

AP CHEMISTRY UPDATE

Chapter 3 Practice Test Answers can be found here and the PowerPoint file that was used in class can be found here. For those of you who wanted more Chapter 3 practice problems, you can find them here.

E-mail me if you have questions, and/or come see me during Mustang Morning. The Chapter 3 Test will be given out on Friday. It will be a take-home test, due on Monday Morning September 19th.

What's the Matter?

Here is a brief summary of the work that was done in Advanced Chemistry this week.

MONDAY = Labor Day holiday
TUESDAY = Review for Unit 1 Test
WEDNESDAY = Unit 1 Test
THURSDAY = Introduction to Matter

FRIDAY = Lab experiment on Physical and Chemical Changes


Unfortunately many students did not perform well on the Unit 1 Test. Students will be given extra practice problems to reinforce concepts that they have not mastered yet. Students who did poorly on the Unit 1 Test should start coming in regularly during Mustang Morning. Students are strongly encouraged to improve their study habits, make flash cards, ask questions in class, and practice solving problems outside of class.

The PowerPoint file "Introduction to Matter" is now available on my web site. Click here to watch it again if you missed anything from the notes in class.

In AP Chemistry, students have completed the Chapters 1&2 Test and turned this in on Tuesday. They have been working on solving problems in Chapter 3, which deals with mass and mole relationships (stoichiometry). Students should become familiar with the techniques for solving these types of problems. Many examples can be found in the textbook. Answers have been posted to the FRQ and MCQ problems and these documents can be found in this folder on my web site. On Monday we will do a lab experiment involving formulas for hydrates and calculating empirical formulas from mass data. The homework for Monday is to answer the pre-lab questions that were given out at the end of class on Friday.

Chemistry Update

Here is a brief look back at the week of August 29 - Sept 2.

AP Chemistry

I have completed our discussion of Chapters 1 and 2, and you should be working on your take-home test over the Labor Day weekend. E-mail me with questions. I expect to receive your completed test on the morning of Tuesday, September 6th.
At this point we have basically completed our discussion of Chapter 3 concepts, including mass-mole relationships and stoichiometry. I'll give you Chapter 3 practice problems on Wednesday and the Chapter 3 test will be coming soon.

Advanced Chemistry
Here is a summary of the activities from this week:
On Monday, we finished up the laboratory involving the density of colored liquids. We also finished reviewing the packet entitled "Math Concepts Used in Chemistry." Then I gave a Math Assessment, which hopefully gave everyone a good idea of whether or not they should start coming to Mustang Morning for some math assistance.

 On Tuesday, we looked at SOL Chemistry questions in the Scientific Investigation strand. If students would like to practice answering Chemistry SOL questions, they can visit the Jefferson Lab website and select Chemistry. 

When prompted for more options, you can select the "Scientific Investigation" strand.

On Tuesday students started taking notes from a PowerPoint slide show presentation entitled "Scientific Notation and Dimensional Analysis." This PowerPoint slide show can be viewed on my website by clicking here, and the handout for these notes can be found by clicking here.

On Wednesday, I gave students the opportunity to practice conversion problems using dimensional analysis. I explained that a conversion factor is a ratio that allows you to convert from one unit to another. Some problems have only one step, but other problems require 2 or 3 conversion factors. It is very important to write down the units during every step, so that you can clearly see how to cancel them out.

On Thursday, we did a measuring activity using small wooden or plastic blocks. The students learned that when a measurement is made with a ruler, the final digit is an estimated digit. This final digit can be a "zero" if the measurement is exactly on the line.We also discussed the concepts of precision, accuracy, significant figures, and graphing. The PowerPoint slide show for these notes can be found on my website by clicking here, and the handout for these notes can be found by clicking here.

On Friday, we did a lab activity using rubber stoppers. Students used the technique of water displacement to calculate the volume of the stoppers. Then they plotted their mass and volume data on a graph, as a way of determining the density. When mass is on the y-axis and volume is on the x-axis, the slope of the line equals density.

HOMEWORK: Students should study their notes completely. Then they should complete the Unit 1 Practice Test, which can be found by clicking here. This practice test will be reviewed in class on Tuesday. The Unit 1 Test will be on Wednesday. E-mail me with any questions. When you come to class on Tuesday, you should be well-rested and ready to learn! Have a great weekend.