LO’s? What The…….?

July 15, 2013

Just in case you don’t know, there are now 117 Learning Objectives (LO’s) (starting on page 100 of the new course description) defined in the new AP Chemistry curriculum. These statements are what you can mine down to, avoiding some of the edubabble and difficult to understand language in the Big Ideas, Enduring Understandings and Essential Knowledge, to get a handle on the fine detail of what’s required in teaching the new exam. In a nutshell, the LO’s are the statements of examinable content that I have been calling for over a decade, and they are modeled by similar statements that have appeared in many standardized exam syllabi for decades.

My Study Guide

My Study Guide

Frankly I always thought that it was not possible to have a nationally standardized test without them – the College Board seems to have finally caught up with me and the rest of the world!

The LO’s are crucial for another reason. Every single sample question that has been written so far (and presumably every single exam question that will be written in the future), has been written with a specific LO in mind. Therefore, any question that you ever see on the AP exam, must be associated with a specific LO. That’s why the LO’s are worth a closer look.

Having said that, even when one mines down to the LO’s, even ignoring the edubabble, there are quite a number that are not at ALL clear to me. With a large body of old AP questions to reference, this wouldn’t matter, since we could look back on what had been asked in the past and be fairly confident about how the LO’s had been interpreted. Obviously at this stage in the new curriculum that is something that we don’t have, so the problem is a little more profound.

Some of the LO’s can be elucidated by retracing steps up one level in the Big Idea-Enduring Understandings-Essential Knowledge-Learning Objective hierarchy, but others aren’t really helped by that.

This post is a summary of my thoughts on LO’s that have varying degrees of clarity to me. Any LO’s that I am (currently) 100% happy about in terms of their meaning and interpretation, do not appear in this post, but ones that need more thought, are included.

Big Idea 1

1.11 – The student can analyze data, based on periodicity and the properties of binary compounds, to identify patterns and generate hypotheses related to the molecular design of compounds for which data are not supplied.

I have no problem with the periodicity part of this statement, but is ‘binary compounds’ a reference to acidity and basicity of oxides? As for the words that follow the word ‘pattern’, wha…..? Is that just a convoluted way of saying kids need to be able to apply periodic patterns??

1.12 – The student is able to explain why a given set of data suggests, or does not suggest, the need to refine the atomic model from a classical shell model with the quantum mechanical model.

OK, electrons are not solid spheres orbiting the nucleus in fixed orbits like planets, but what data might present evidence for or against this? Rydberg equation? Eh?

1.13 – Given information about a particular model of the atom, the student is able to determine if the model is consistent with specified evidence.

Rydberg equation again? Surely not, since that’s no longer on the Equations sheet.

While I *think* I know what 1.12 and 1.13 are saying, I cannot imagine how they will be asked in an AP question.

1.15 – The student can justify the selection of a particular type of spectroscopy to measure properties associated with vibrational or electronic motions of molecules.

The first thing that came to mind here was the use of different types of organic based spectroscopy to distinguish between isomers or very similar compounds as asked in this example question. A few minutes of reflection had me running away from that particular scenario, and has me looking at the essential knowledge that follows 1.15, i.e., 1.D.3b. This suggests that we are talking about a simple distinction between using IR to detect different types of bonds, and UV and visible to investigate electronic transitions, including color. How will this be asked? Is this simply an extension of Beer’s Law (see LO 1.16), or does it simply mean; Ionization Energies = PES, Beer’s Law = Spectrophotometer, Emission/Absorption Spectra  = Spectroscope??

1.16 – The student can design and/or interpret the results of an experiment regarding the absorption of light to determine the concentration of an absorbing species in a solution.

This is a classic case of convoluted BS as far as I can tell. Why doesn’t it simply say, ‘Students need to understand and be able to apply Beer’s law’??

Big Idea 2

2.2 – The student is able to explain the relative strengths of acids and bases based on molecular structure, interparticle forces, and solution equilibrium.

Is 2.2 really expecting students to know about the stability of carboxylic anions in relation to electron withdrawing and releasing groups and their relative position in carbon (R) chain?? I suspect, and hope not, but the words ‘molecular structure’ have me wondering.

2.7 – The student is able to explain how solutes can be separated by chromatography based on intermolecular interactions.

2.10 – The student can design and/or interpret the results of a separation experiment (filtration, paper chromatography, column chromatography, or distillation) in terms of the relative strength of interactions among and between the components.

I’ve no real issue with either of these statements as entities, except that I don’t really don’t see how these things are different from one another in terms of chromatography, meaning why does 2.7 need to exist in addition to 2.10?

The same is somewhat true of 2.17 and 2.18 below – what’s the real, tangible, AP chemistry question difference here?

2.17 – The student can predict the type of bonding present between two atoms in a binary compound based on position in the periodic table and the electronegativity of the elements.

2.18 – The student is able to rank and justify the ranking of bond polarity on the basis of the locations of the bonded atoms in the periodic table.

While we’re on the subject, how exactly is 2.20 significantly different to 2.26, and for that matter, 2.28? Isn’t this just ‘Students need to know about metallic bonding and associated properties’?

2.20 – The student is able to explain how a bonding model involving delocalized electrons is consistent with macroscopic properties of metals (e.g., conductivity, malleability, ductility, and low volatility) and the shell model of the atom.

2.26 – Students can use the electron sea model of metallic bonding to predict or make claims about the macroscopic properties of metals or alloys.

2.28 – The student is able to explain a representation that connects properties of a metallic solid to its structural attributes and to the interactions present at the atomic level.

The same is true of the relationship between 2.29 and 2.30, AND 2.31 and 2.32.

2.29 – The student can create a representation of a covalent solid that shows essential characteristics of the structure and interactions present in the substance.

2.30 – The student is able to explain a representation that connects properties of a covalent solid to its structural attributes and to the interactions present at the atomic level.

2.31 – The student can create a representation of a molecular solid that shows essential characteristics of the structure and interactions present in the substance.

2.32 – The student is able to explain a representation that connects properties of a molecular solid to its structural attributes and to the interactions present at the atomic level.

It seems as though all of these groups of LO’s could have been simplified to read;

Students should;

  • Understand the structure of metals and how it relates the properties of metals
  • Understand the structure of covalent solids and how it relates the properties of covalent solids
  • Understand the structure of molecular solids and how it relates the properties of molecular solids

See, much quicker and half of the LO’s!

2.21 – The student is able to use Lewis diagrams and VSEPR to predict the geometry of molecules, identify hybridization, and make predictions about polarity. 

I am not remotely concerned about 2.21 as an entity, but if one looks at Essential Knowledge 2.C.4i, then I get nervous. I have NO idea how MO can be asked. Here’s what I wrote on a recent AP discussion group post in response to a question from Marion Carson about how MO might be incorporated into 2.21.

Marion – this is a GREAT question, and it is one that is repeated in a whole bunch of other places within the new curriculum for me; there are LOTS of places (LO’s and EK) that I am asking myself, ‘what does this mean, and how can it be asked on the exam?’. Here’s what I would offer up;

1. In order for a question to appear on the exam, it is my understanding that it HAS to directly relate to a LO. It is true that the EK should help to enlighten us about the LO’s, but as you observe, LO 2.21 makes no mention of MO, so as far as I am concerned, for now at least, forget it!

2. I take EK 2C4i to simply mean that kids ought to know that VSPER has its limitations, and sometimes you need a more complicated theory (MO) to work stuff out regarding shape and molecular structure. As I say above, how the heck that would be asked on the exam AND be kept within the limitations of LO 2.21, I have NO idea at this point!

3. If you look at the practice exam there are two questions that reference LO 2.21, and neither of them have anything to do with MO. There is nothing in the course description that helps to explain LO 2.21.

Given that the practice exam and the course description are all that we have to go on, and what I have written in 1 and 2 above, for me, MO is basically a non-entity at this stage. Of course, when more information comes to light (like a few years worth of exams), maybe I will change my mind, but for now that’s all I have.

Big Idea 3

Nothing here bothers me – yet!

Big Idea 4

The LO’s of Big Idea 4 have some very convoluted language once again. I sought some clarification on the following from the College Board and below is a summary of those exchanges.

Here is are my original questions in blue, with responses in green that follow.

What does the second half of LO 4.3 mean?
 
4.3 – The student is able to connect the half-life of a reaction to the rate constant of a first-order reaction and justify the use of this relation in terms of the reaction being a first-order reaction.
 
Does it simply mean that the student should know that first order reactions have constant half-lives?

I’d say yes, any analysis of supplied  data will show half life to be a constant which is independent of the starting concentration.  This tags the order automatically to be first.  However, with the other common orders, half life for a zero order reaction decreases with decreasing concentration, and half life for a second order reaction actually increases with decreasing concentration.

In LO 4.8, what might a ‘particulate representation ‘ of a reaction involving a catalyst look like?

4.8 – The student can translate among reaction energy profile representations, particulate representations, and symbolic representations (chemical equations) of a chemical reaction occurring in the presence and absence of a catalyst.

I DON’T think it means a lock and key enzyme diagram (since that looks like 4.9 to me), but could it mean something like this or this (although that looks a lot like lock & key) or even this?? Having said that, the first and third examples that I give above, look like ‘surface catalysts’ to me, so they could be covered in 4.9, too.

I think those are probably appropriate representations, even though 2 looks lock and keyish.  It could also involve particulate drawings showing the involvement of the catalyst species with a reactant drawn on an energy profile, indicating a different path with a lower activation energy.  Also, different size particles of the catalyst (the role of surface area) could be represented to deduce a different path with a lower activation energy.

Does this mean you might see a energy profile where the physical position of the reactants with a catalyst, is literally placed at a different position on the y-axis than the physical position of the reactants without a catalyst?
 
I think this could be a possibility.

In LO 4.9, is the second half of the statement simply asking students to recognize a catalyst in a reaction mechanism (with no particular, specific reference to acid/base, enzyme or surface)?

4.9 – The student is able to explain changes in reaction rates arising from the use of acid-base catalysts, surface catalysts, or enzyme catalysts, including selecting appropriate mechanisms with or without the catalyst present.

I’m thinking not, since my interpretation of the middle of 4.8 (‘symbolic representations (chemical equations) of a chemical reaction occurring in the presence and absence of a catalyst’) would cover that.  However, I suppose I could be misinterpreting 4.8! Basically I am stuck on ‘selecting appropriate mechanisms with or without the catalyst present’. This doesn’t mean simply choosing a mechanism from a list of proposed ones, does it?

It pretty much explains what the student should know and recognize in EK 4.2 a, b, and c, (gain/lose proton, modify successful collisions, bind to form intermediates) as well as see if the mechanism follows the “rules” as , adds up to the overall reaction, shows intermediate(s) and or catalyst(s),  rate determining step identified.  It could be selecting an appropriate mechanism, or perhaps showing how the proposed mechanism properly fits a rate equation.

In understand EK 4B1 completely, but LO 4.4 is a mystery to me. Does it simply mean that kids should know;

a. That at a fixed temp, as [ ] increases, so will the frequency of collisions, so the rate will go up without changing k, but that

b. With fixed [ ], rate will increase with increasing temp since k will increase?

4.4 – The student is able to connect the rate law for an elementary reaction to the frequency and success of molecular collisions, including connecting the frequency and success to the order and rate constant, respectively.

The relationships between temperature, collision frequency, rate, rate constant and the rate equation are clear to me, but what is not clear is what this LO is asking about in terms of the relationship between ‘successful collisions’ and the rate equation. Does it simply mean that students should appreciate that the greater the number of successful collisions, the faster the rate?? It can’t simply mean that, can it??

Well, elementary reactions are one step processes going from reactant to product without an intermediate, usually unimolecular or bimolecular.  The rate is dependent on the frequency of collisions between the particles in that step.  Collision theory says that the rate is proportional to the number of effective collisions between the reactants.  So LO 4.4 basically says this is what students should get—  If the concentration increases, there are more total collisions,  the greater the frequency, the greater the number of effective collisions, if the frequency of effective collisions increases, so does reaction rate.  Of course, the rate constant is dependent on the order of the reaction.

‘Rate constant is dependent upon orders’? – So you mean kids have to known that the frequency of collisions affects the ‘A’ value in the Arrhenius equation, and therefore the rate constant? Would an alternative be to have a qualitative treatment of Arrhenius with the orientation factor added or should we have that, IN ADDITION?

Yes, students should know that.  I’d say that orientation importance needs to be stressed in addition.

LO 4.6 just means qualitative understand Arrhenius, correct?

4.6 – The student is able to use representations of the energy profile for an elementary reaction (from the reactants, through the transition state, to the products) to make qualitative predictions regarding the relative temperature dependence of the reaction rate.

Yes, they won’t be solving it but must understand the implications of a change in temperature on the rate constant.

Big Idea 5

5.15 – The student is able to explain how the application of external energy sources or the coupling of favorable with unfavorable reactions can be used to cause processes that are not thermodynamically favorable to become favorable.

I did a decent amount of research about this, and the associated Essential Knowledge statements that refer to ADP and ATP, but as far as I can tell, this is absolutely nothing other than summing Delta G’s. If that’s true, it’s a hell of a complicated way to ask such a simple piece of theory! Similarly 5.16 and 5.17 seem to be not much more than combining K’s!

5.16 – The student can use Le Chatelier’s principle to make qualitative predictions for systems in which coupled reactions that share a common intermediate drive formation of a product.

5.17 – The student can make quantitative predictions for systems involving coupled reactions that share a common intermediate, based on the equilibrium constant for the combined reaction.

Big Idea 6

6.23 – The student can interpret data regarding the relative solubility of salts in terms of factors (common ions, pH) that influence the solubility.

I think that in most cases, pH can be thought of in terms of common ions, too. We’ll see

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