Gas Laws Test

Tomorrow (Wednesday, April 11th, 2012) is the test covering gas laws. Below are four short review problems and the solutions to the problems. The review problems are optional. All material on all worksheets is fair game for the exam. The complete keys for the Combined Gas Law Worksheet and Ideal Gas Law Worksheet can be found the Events Calendar of the class web-site. Please look over the Manometer Worksheet that was done early in the chapter. All calculator skills are fair game for the exam. The exam will consist of 22 multiple choice questions. You will be given all equations, constants and conversions factors for the exam. Come and see me before the exam is you have any questions.

More Electro Chemistry Review Material

Below are images of the review sheet given in class. The two answers for questions #13 and #14 are #13 lead and #14 aluminum. I have also included the key to the group quiz given yesterday in class. The test tomorrow consists of 22 questions. The questions are a combination of multiple choice and written responses. On the class Events Calendar under today's date, I have posted a pdf file of the key to the half reactions worksheet if you would like to review that material. I will be at school by 6:50 tomorrow if you need to ask me any questions.

Review for Electrochemistry Test

Below are keys to materials that are useful for you to review for the test on Electrochemistry that will be given on Thursday, March 15th, 2012. On the Events Calendar date of Tuesday, March 13th, 2012, two files can be found for reviewing for the test. Tomorrow, Wednesday, March 14th, most of the class period will be spent reviewing for the exam.

Chemical Reactions Review

Below is a solutions guide to the optional review for tomorrow's test on chemical reactions. The test will consist of 28 multiple choice questions and seven short answer problems. The multiple choice part of the test will cover balancing reactions, classifying types of reactions, use of an activity series for predicting if reactions will occur, and use of a solubility table. The short answer problems will be like those on the Chemical Reactions Review that you worked on in class today. A complete VODCast key for the Chemical Reactions Review is available on the class Events Calendar on the date Tuesday, February 21st, 2012. The only type of reaction that you will be held accountable on to know the state of matter will be double replacement reactions. Below the key for the optional review is a brief tutorial on how to balance equations. Come and see me tomorrow morning if you have any questions.

For those of you experiencing a little difficulty on the balancing chemical reactions worksheet, I have some advice for a possible sticking point.

Elements combine in whole number, that we know to be true. Thus, we need to have the smallest whole number ratio of the coefficients used to balance the equation. To balance an equation initially, you may use a fraction, but then you must modify the coefficients to make them whole numbers. Below is an example.

Reaction: C3H6O2 + O2 --> CO2 + H2O

Hint: Wait to balance oxygen last since placing a coefficient in front of elemental oxygen (O2) will not change any other elements.

Initial balancing: C3H6O2 + ?O2 --> 3CO2 + 3H2O

The carbons and hydrogens have been balanced. All that is left are the oxygens. There are a total of 9 oxygens of the product side (right of the arrow). Notice that 2 oxygens exist in the compound on the reactant side. Thus, to balance out the oxygens, an equation can be set up.

2 + x = 9 --> x = 7 --> Seven oxygens are required to balance the reaction, so this dictates that we use a coefficient in front of oxygen (O2) that will produce 7 oxygens. This will cause a coefficient of 3.5 to be used. This is not a whole number, but we can deal with that later.

Almost balanced: C3H6O2 + 3.5O2 --> 3CO2 + 3H2O

Having a fraction as a coefficient is not allowed, thus we must convert 3.5 to a whole number. To accomplish this, we will multiply 3.5 by 2. Just like in algebra, if something is done to one number, we must do the same thing to all of the numbers. Thus, all coefficients will be multiplied by 2. Doing this keeps the equation balanced.

Almost, nearly balanced: 2(C3H6O2 + 3.5O2 --> 3CO2 + 3H2O)

BALANCED!! 2C3H6O2 + 7O2 --> 6CO2 + 6H2O

Make sure that you check all of the elements on each side of the reaction to ensure that is has been balanced correctly.

Key for Word Equations Worksheet

Below is the key for the "Word Equations" worksheet. A common mistake made is forgetting which elements are diatomic elements. The elements hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine all are two atom molecules when isolated alone in nature. The VODCast for the "Chemical Reactions Review" has been posted under the date Friday, February 17th, 2012. The "Chemical Reactions Review" problems are on the back of the Word Equations worksheet. Please do the example problems before class on Tuesday, February 21st, 2012. The problems that are not shown as examples will be completed by you with your work groups in class on Tuesday. After classes are complete on Tuesday, another VODCast with all of the solutions to the review will be posted. The test for the chemical reactions unit will be given on Wednesday, February 22nd, 2012.

The chapters in the book that cover this material are Chapter 6 and Chapter 7. Sections 7.4 and 7.5 will not be covered by Wednesday's test. They will be covered later in the semester.

Quiz Review for Wednesday, February 15th, 2012

Tomorrow (Wednesday, February 15th, 2012) will be a quiz over balancing equations, classifying types of reactions, the use of the activity series chart, and the use of the solubility table. The types of reactions were given in your notes, but I will summarize them again in this blog post. The types of reactions and how they are abreviated are shown below. The key to the types of reactions on the balancing reactions worksheet are given below.

• synthesis reactions (shown as "syn" below) - less complex atoms or molecules become more complex molecules. Remember, a three element compound is more complex than a two element compound.


• decomposition reactions (shown as "decomp" below) - more complex molecules become less complex molecules or atoms. A two element compound is less complex than a three element compound.


• dissociation reactions (shown as "diss" below) - ionic compounds, when placed in water, dissolve in water to go from solid to aqueous. The aqueous products will always be shown as ions with charges.


• combustion reactions (shown as "comb" below) - elements oxygen (O2) must always be a reactant. Each product must contain the element oxygen. **All hydrocarbons (compounds that contain the elements carbon, hydrogen, and sometimes oxygen), when combusted, produce the products carbon dioxide and water. Both CO2 and H2O have oxygen in them.


• double replacement reactions (shown as "D.R." below) - two aqueous ionic compounds switch ions. The metal (positive ion) of one compound possibly combines with the non-metal (negative ion) of another and vice-versa. A new state of matter matter must be produced. This is usually a precipitate (solid), but not always.


• single replacement reactions (shown as "S.R." below) - a single element and an ionic compound are reactants. A general rule is "a metal replaces a metal and a non-metal replaces a non-metal" for single replacement reactions. If the single element is a metal and is more active than the metal in the ionic compound, the more active metal will replace the less active metal in the compound. Example #1: Cu +2AgNO3 --> Cu(NO3)2 + 2Ag OR a more active non-metal will replace a less active non-metal in the ionic compound. Example #2: Cl2 + CaBr2 --> CaCl2 +Br2. A metal or non-metal's reactivity can be determined by where it is on the activity series chart given in class. If a less active element is the element by itself, it will not replace the more active element. This will be classified as a NO REACTION (N.R.)

**Some reactions can have more than one type of classification. This often occurs with synthesis reactions that involve elemental oxygen as a reactant. They can be often be classified as combustion reactions also. Also, some of the reactions in the worksheet do not always fit nicely into a category, so that is indicated by a question mark. You will not be given any questionable reactions on the quiz.

The quiz will require you to do the following:

• Balance equations and classify them just like the work sheet given in class.


• You will also be shown single replacement reactions and asked to predict if a reaction will occur because the single element reactant is more active than its like element in the compound or the reaction will not occur because the single element reactant is less active than its like element in the compound.


• You will be given ionic compounds, and using a solubility table, determine if the compound is soluble in water (aqueous) or not soluble in water (solid).

**You will be able to use your own periodic table and solubility / activity series table on the quiz. The quiz will be going into the "Assessment Category" of your grade.

New VodCast - Writing Double Replacement Rxns

The new VODCast showing how to write double replacement reactions for the Observing Chemical Reactions in Solution Lab is available on the Events Calendar under the date Saturday, February 11th, 2012. Please view it prior to class on Monday to prepare for the lab. Have a good weekend.

Keys for Naming and Writing Chemical Compound Formulas

Below are the answer keys to all of the worksheet given in class on naming and writing compound formulas. There will be a diagnostic quiz given on Wednesday, February 1st, 2012 to assess your mastery of the material. If you do not feel comfortable with the material after Wednesday's quiz, on the Events Calendar under the date Wednesday, February 1st, 2012 is a VODCast that you can watch for remedial help. A worksheet is available for more practice. The VODCast covers all of the material presented on the worksheet. There will be a quiz that will go in the Assessment Category of your grade on Friday, 2/3/2012. Also on that Friday, a quiz will be given over your general science knowledge. Any points earned on that exam will be given to you as extra credit towards your Assessment Category. The points will be pro-rated.

Major Exam, Wednesday, 1/25/2012

Your first major exam of the semester will be on Wednesday, January 25th, 2012. I have not finished writing the exam yet, but I can tell you that the test will be between 30 and 40 questions. It will be mostly multiple choice with a few free response questions. Below I have written out the key concepts that you need to be aware of to do well on the exam.

• Be able to complete a Lewis dot structure for a compound given.



• Based upon a Lewis dot structure, you must be able to determine the parent geometry, number of ligands around the central atom, number of bonding and non-bonding ligands around the central atom, and the molecular geometry.



• Know that non-bonding ligands on the central atom repel more than bonding ligands. This has an influence on the bond angles. Example: tetrahedral molecular geometry (4 bonding ligands) has a bond angle of 109.5^o; trigonal pyramidal molecular geometry (3 bonding ligands and one non-bonding ligand) has a bond angle of 107^o; and bent molecular geometry (2 bonding ligands and 2 non-bonding ligands) has a bond angle of 104.5^o. You will be supplied a table of parent and molecular geometry names and the angles associated with each molecular geometry. An image of the table is at the bottom of this post.



• Based upon molecular geometry and the ability to visualize a 3-D model of the molecule with dipoles (based on electronegativities), determine if the molecule is polar or non-polar. This is based upon the symmetrical or asymmetrical distribution of charge around the outside of the molecule.



• Based upon the polarity of the molecule, determine the type of intermolecular bonds that would occur between molecules of the same type.



• Non-polar molecules will experience only London dispersion forces.



• London dispersion forces are the weakest of the types of intermolecular bonds. They are created by a temporary dipole randomly occurring across a molecule do to movement of electrons within the molecule. London dispersion forces strength difference comes from the different sizes of molecules. Larger molecules have more surface area for bonding and more electrons to create a greater temporary dipole.



• Polar molecules can experience dipole-dipole forces or hydrogen bonding intermolecular forces. Dipole-dipole forces are stronger than London dispersion forces. Hydrogen bonding is a special type of dipole-dipole force because it occurs between polar molecules that contain hydrogen covalently bonded to fluorine, oxygen, or nitrogen. Hydrogen bonding is the strongest of the intermolecular bond types.



• Know the reasons why hydrogen bonding is the strongest type of intermolecular bond. (1) The atoms (H, F, O, and N) are all small atoms which allows for the molecules to fit in close together for stronger bonding. (2) The large electronegativities of fluorine, oxygen, and nitrogen create a large charge separation when covalently bonded to hydrogen. (3) Hydrogen has no core electrons. When hydrogen's one electron is closer to the other atom in a covalent bond due to the other element being more electronegative, the proton of hydrogen is completely exposed. (A.k.a. - hydrogen is a mooner)



• **Please note: The strength of the intermolecular (between molecules) bonds are only to be compared to one another. Both ionic bonds and covalent bonds between atoms (intramolecular) are much stronger than any of the intermolecular bond types (London dispersion, dipole-dipole, hydrogen bonding).



• **Please note: All molecules experience London dispersion forces. This is why the size of the molecule (more surface area / more electrons for temporary dipole formation) is the indicator of intermolecular bond strength when the type of intermolecular bonds are the same when comparing more than one molecule.



• Know how the concepts of melting/freezing point, boiling/condensation point, heat of fusion, and heat of vaporization are based upon intermolecular bond strength. (1) low values of all of the concepts listed will have weaker intermolecular bonds. (2) high values of all of the concepts listed will have stronger intermolecular bonds.



• Know how to compare intermolecular bond strengths on the values of joules or kilojoules per mole. Know that the mole concept is needed to accurately assess bond strength do to the amount of energy used in comparison with the number of bonds broken. This comparison cannot be made with energy value per gram of substance.



• Know the graphical concepts of the Intermolecular Bond Strength / Vaporization lab. Know how the graphs of the lab were interpreted. The weakest intermolecular bonding type belonged to acetone, so it finished evaporating first. This was indicated by the temperature on the graph for acetone beginning to rise first. Once all the acetone had evaporated, energy was no longer being taken from the temperature probe to evaporate the liquid acetone (break bonds between the molecules). Energy from the room then went back into the temperature probe to raise the temperature of the probe. Intermolecular bond strength was determined by when the temperature increase occurred. The longer it took for the temperature to rise again, the stronger the intermolecular bonds.



• Be able to look at a phase change (Temperature vs Time) graph and determine the state of matter and (melting/freezing) / (boiling/condensation) points of a substance.



• Know that heat of fusion and heat of vaporization calculations would take place at the plateau's of the graphs.



• Know that any sloped part on a phase change graph would require (q=s x m x delta T) to determine the amount of energy associated with the change in molecular motion of the substance.



• Know how to solve for any variable associated with the heat of fusion or heat of vaporization equations.



• Be able to calculate the total amount of energy associated with the heating or cooling of a substance. This would involve multiple calculations using the heat of fusion and/or heat of vaporization with (q=s x m x delta T).



• THERE WILL BE NO QUESTIONS ABOUT THE ENERGY NEEDED TO MELT ICE LAB.



• Look at all material used for the unit of study. Watch the VODCast of the first work packet done in class. A key (pdf file) for the second work packet is posted on the Events Calendar under the date, Monday, January 23rd, 2012.



• You will get to use your periodic table. I will supply you with an electronegativity table and a copy of the diagram below. You will also be supplied with all equation for the exam.

Practice For Your Quiz Tomorrow!

On Monday, January 23rd, 2012, you will be taking a quiz covering the material presented in the"Energy Needed to Melt Ice Lab". I have made a VODCast showing a summary of the lab procedure, concepts associated with the lab, and how to perform the calculations associated with the lab. The VODCast is posted on the Events Calendar of the class website under the date Sunday, January 22nd, 2012. You will be given all of the equation needed to complete the exam.

After you complete the quiz, we will be using the remainder of the time in class to review for the major exam that will be given on Tuesday, January 24th, 2012. You need to have the 2nd work packet for Heat of Fusion / Vaporization completed tomorrow before class to receive credit for the work done on the packet.

VODCast for Heat of Fusion / Vaporization Packet

The VODCast for parts (A) through (G) of the Heat of Fusion / Vaporization Work Packet has been posted under the date Tuesday, January 17th, 2012 on the class Events Calendar. The remaining problems (H through M) will be completed in another VODCast by tomorrow. Remember, all parts of the work packet must be completed prior to class on Thursday, January 19th, 2012. On that day, you will get another packet of questions and problems that you will complete with your work groups using the "flipped" classroom model.