Normally I do not share any of my tests, but since we are still largely in the dark about the exact nature of Net Ionic Equation Writing on the 2007 AP Exam and beyond, I would like to get some feedback on what I put in front of my students as being my “best guess” for what may appear in May 2007. Please take a look and let me know what you think, but when you do consider the following context;
1. With the new requirement to balance AND with choice removed, I think it is going to to be very difficult for the CB to ask some of the more complicated REDOX equations that require “difficult to balance” half-reactions. As a result, on this test I purposely included MANY less of the complex redox reactions than I have in the past. (I think that Manganate (VII) and Dichromate(VI) are very much IN play, but disproportionation and other more difficult redox are less likely to appear – just my guess).
2. In the absence of any other knowledge I graded the test thus;
Each set of three questions was out of a total of 15 points. Each question was awarded points in this manner;
1 point for “perfect” reactants (ignoring coefficients, but there must be ALL the reactants present and NOTHING else).
2 points available for products. partial credit (i.e. 1) was available here.
1 point for balancing, but this was only awarded if at least 1 out of 3 was scored on reactants and products part, AND charges balanced too.
1 point for the question that followed.
3. The usual restrictions and copyright notices apply.
The test can be viewed here; AP TOPIC 12 TEST 2007
Adrian:
Your reaction questions seem entirely plausible and reasonable. Below I have listed some of my own questions for the reactions that you have given. Please let me know what you think.
-Michael
1a.
If a solution of barium hydroxide had been used in this reaction instead of lithium hydroxide, how would the appearance of the reaction have been different?
If a pH meter were inserted into the lithium hydroxide solution, how would the pH have changed when the sulfuric acid was gradually added to the solution?
Lithium hydroxide is classified as a strong base. Name one example of a weak base.
Sulfuric acid is classified as a strong acid. Name one example of a weak acid.
1b.
If potassium iodide had been used as a reactant instead of potassium chloride, describe the physical appearance of the product of this reaction.
Identify the spectator ions in the reaction mixture.
NOTE: I’m curious if you think that a question about spectator ions might be “too easy.” I know that it was listed as one of the examples by Eleanor Siebert, but I am thinking that perhaps it would give the students too much of a “hint” about the type of reaction. Suppose a student forgot to exclude the spectator ions when he wrote his reaction. If he reads a question asking him to identify the spectator ions, don’t you think that this would remind him of his error? Is that somehow “giving away” the answer? Of course students still have to know their solubility rules, but it’s just a thought that I had.
1c.
Identify the product as acidic, basic, or neutral.
NOTE: In my opinion, I think it is better to ask them if the substance is an acidic, basic or neutral. Alternatively, you could ask them a question about the pH. I think that if you mention that the litmus paper is blue to begin with, then it allows the possibility for a lucky guess. If I am a student who doesn’t know much about my acid-base chemistry, I might just guess that a piece of blue litmus paper is going to change to red, without really knowing why it does that.
How would the products of this reaction be different if sulfur trioxide were bubbled through water?
Identify the oxidation number of the sulfur atom in the product.
2a.
When copper metal is added to a solution of magnesium sulfate, predict whether or not a reaction will occur.
If excess magnesium is added to a dilute solution of copper sulfate, describe the change in color of the solution that takes place as the reaction proceeds.
2b.
Identify the color of the solution at the end of the reaction.
2c.
The carbonate ion and the nitrate ion have the same molecular geometry. Identify the shape of these ions.
Potassium carbonate behaves as a base when it is dissolved in water. Write a net ionic equation to explain this fact.
3a.
Identify the change in the oxidation number of the chloride ions as the reaction proceeds.
Identify another chemical reagent that could perform the same role as the hydrogen peroxide does in this reaction.
3b.
Draw the cis and trans forms of 1,2-dichloroethene.
3c.
Describe how you could use a magnet to determine if this reaction has gone to completion.
How does the oxidation number of the Fe change during the course of this reaction?
4a.
Write the formula of the product that would be formed in this reaction if carbon dioxide gas is replaced with sulfur dioxide gas as a reactant.
Classify calcium oxide as acidic, basic, or neutral.
4b.
How does the pH of the water change when sodium hydride is added to it?
Give the symbol of a neutral atom that is isoelectronic with the hydride ion.
4c.
How does the pH of the water change when sulfur tetrachloride is added to it?
Identify the hybridization of the central atom in the sulfur tetrachloride molecule.
Hi Michael
Good stuff, thanks for your input, pretty much all valid I feel. Here are a few more comments about your comments!
1b, Spectator Ions: Well, WHO KNOWS!!?? Since Eleanor gave that as an example, why not!? We have so precious little to go on that I can’t really say any more than that. I DO take your point about the question giving a hint about the equation, and I have struggled with that myself, but until we either have more specimen material, or a significant bank of old questions to reference, it really isn’t going to be possible to answer that question.
1c, Guesses: I take your point, but I ONLY gave the point if they said “Red” (not just any color change) and if you asked, “acid, base or neutral” instead that hardly eliminates the possibility of guessing, does it?
3b, Organic: I think cis/trans knowledge would certainly be beyond what has been expected of kids recently, but I still wouldn’t be astonished if I saw a question like that (even though it’s probably a “dead” point for 50-75% of the kids). N.B. I KNOW that 2004B, 8 DID have the cis/trans isomers of but-2-ene, BUT knowledge of what cis/trans means was not relevant to the question, it was about equilibrium. That is true of virtually all recent instances of organic on the exam. Basically some organic molecules have been used to illustrate OTHER theory like Bonding for example, and the questions have required virtually no organic knowledge. This has confused some kids because they see an organic molecule and automically think it is an organic question.