Question 1:

For the first time in over a decade, the equilibrium question repeated a K theme in consecutive years. Very straightforward, solid chemistry here, nothing to report. BTW – Ka and molar mass suggest that HA is benzoic acid.

Question 2:

Quite a novel way to test some combustion analysis, and I think it will have made lots of quite able kids think a lot – in that respect I like it. I also like the originality of the question for such a simple reaction and situation, so in that respect, good. There are many different ways to solve (b), (c) and (d) which means this could be a pain to grade!

Question 3:

They called ethene, ‘ethene’ and did NOT reference ethylene – HOORAY FOR IUPAC!

(a), (b) and (c) are uninspiring to say the least, but like question 2, (d) and (e) show some originality.

Question 4:

As we all know, the net ionic equation writing has been a shadow of its former self of late but this reaches perhaps an all time low. This question is close to being an embarrassment for an AP exam. I think it’s a terrible shame that the NIE’s have been decimated over the years, but this takes the cake. Someone at the CB/ETS ought to be ashamed.

Here’s a few ways to make this question better;

(a) – Make the acid weak, and then follow up with a question about testing for CO2 (limewater test).

(b) – Almost ANYTHING would help here! Formation of magnesium nitride perhaps?

(c) – Ask about excess hydroxide ions being added and the formation of a complex and then follow up with a question about THAT. At LEAST don’t FLAG the precipitate!

Question 5:

A pretty easy question but one that will probably be scored very harshly and will result in much lower scores than one might anticipate. The grading of these bonding questions has been really meticulous in the past, to the point of being obsessive, and I bet there will be lots of people that thought they scored full credit that end up with half or less. I don’t see the point of essentially having all five parts ask about bonding, and I think it goes against the idea that questions should be more diverse. It’s really the same thing asked over and over again.

Question 6:

Run of the mill with the exception of (e)(iii) which is NUTS.

(a) – Disappointing, since there are much more imaginative ways to ask about reactivity series, and it would be nice to perhaps talk about OBSERVATIONS (or lack of them) rather than just giving bland equations. Isn’t this the kind of thing they WANT to do more of?

(e)(ii) – I would MUCH prefer it if the question did NOT tell us that a precipitate forms and the kids have to work it out. It would be better that way.

(e)(iii) – I was puzzled at first when I did not see the option of ‘zero’ mentioned in the question (like it had been in (e)(i)), since I thought if the switch is open then the circuit would be broken and the voltage would be zero. I actually got this wrong as a result, until Paul Cohen pointed out that the BIZARRE manner in which the circuit is connected means that even with the switch open, the circuit is still complete. This is VERY, very odd and frankly very, very sneaky. I have no problem with the odd curve ball here and there*, but lets not start asking the kids physics and electricity circuit questions on the AP chemistry exam!

*There is of course a valid argument to say that odd, tricky questions will help to distinguish the very best kids, but when (traditionally) the only distinction for a 5 has been getting in the 60-70% range, if a really great kid misses a single, tricky point, in the end that ISN’T actually going to distinguish him or her from a kid that gets the really hard point.

OK, before you take a look at my FIRST DRAFT answers PLEASE understand the following;

1. They are first draft and will likely containing errors and have omissions.

2. Please let me know what you think, and correct me where necessary.

3. Thanks to the venerable Paul Cohen (veteran chemistry educator, experienced AP chemistry reader and table leader) for picking me up on a couple of minor points already!

Going out a limb is always dangerous, so please be respectful of my willingness to do so! Thanks.

Here are my FIRST DRAFT answers

These nuggets of information are unlikely to form any formal part of many, mainstream chemistry course that is designed to prepare you for these exams, but rather they are accumulated by having knowledge of other, related disciplines (maybe biology or physics), reading around the subject, being aware of scientific or chemical issues in current affairs and the news, or perhaps simply are reliant on some general knowledge – the kind of knowledge that might be obtained by reading ‘science’ articles on Wikipedia or reading a chemical encyclopedia!

Here I have attempted to summarize some of these factoids. By their very nature, any attempt at a compilation can NEVER be ‘complete’ or indeed exhaustive, so please view this list in that light. In fact, I wanted to do a blog post rather than a document, since people can comment, and the list can be more dynamic and can evolve. PLEASE understand this is (and always will be), a ‘work in progress’!

I have tried to gather some very generic headings in order to organize the material, but again, by its very nature, the factoid knowledge is diverse and somewhat random, and can be difficult to categorize in a meaningful way – by definition, it’s somewhat fractured and ‘random’. I hope this helps you to score an extra point or two in your tests!

A. Environmental

a. Greenhouse gases – classically CO₂, but also H₂O and methane. Cause global warming and climate change.

b. Eutriphication – nitrates and phosphates washed into water systems causing excess growth of algae and other organisms and increased stagnation.

c. CFC’s (Chlorofluorocarbons) – Compounds of the halogens, previously used in refrigerants that are known to cause the breakdown of the protective ozone layer around the earth.

d. Hard water – water with calcium and magnesium ions dissolved in it that creates a ‘scum’ with soap and can be difficult to create a lather with. Also buils up ‘limescale’ in pipes leading to blockage, ‘Softened’ by replacing group 2 ions with group 1 ions.

B. Biological

a. Amino acids – Organic molecule important in biological systems. Contains carboxylic acid functional group (-COOH) and amino functional group (-NH2). Can form a ‘zwitterion’ where acid internally donates H+ to NH2.

Amino Acid

Zwitterion

b. Proteins – long polymer chains of amino acids. Crucial biological roles

c. Lipids – large group of naturally occurring biological molecules with various functions. Include sterols, waxes and fats

d. Fats – Primarily triglycerides that are tri-esters derived from glycerol (an alcohol) and ‘fatty acids (acids)

e. Carbohydrates – compounds of carbon and H₂O, often known as the more generic, ‘sugars’

 C. Laboratory Situations (AP)

See separate document, here.

D. Medicine

a. Disinfectants – iodine, hydrogen peroxide

b. Radioactivity – used to attack tumors or track bodily function

E. Qualitative lab tests

a. Gases

(i) CO₂ – turns limewater milky. (Will also extinguish a splint, but not definitive – see N₂)
(ii) N₂ – extinguishes a splint (see CO₂)
(iii) O₂ – relights a glowing splint
(iv) H₂ – ‘squeaky pop’ test with glowing lighted splint

b. Other – see TOPIC 5 notes.

F. Common Colors

See separate document, here.

G. The Elements

a. States – solids at RT, except Br and Hg (liquids) & common gases (H, O, N, F, Cl, noble gases)

b. NOT monatomic

(i) Diatomic (Br-I-N-Cl-H-O-F or H-O-F-Br-I-N-Cl)

(ii) P₄ (white/red), S₈ (rhombic/monoclinic) (However, generally uncommon to use anything other than single P or S atoms in equations)

c. Abundance – listed in order, most abundant first.

(i) Earth’s crust – O, Si, Al, Fe, Ca, Na, K, Mg

(ii) Sea (not including H and O that make up water) – Cl, Na, Mg, S, Ca, K, Br

d. Names – For common groups, see TOPIC 7 notes. Lanthanides – first row of f-block, Actinides – second row of f block

H. Uses of chemicals in Industry/Commercial

a. Semi-conductors – silicon, germanium and other metalloids

b. Ammonia – in fertilizers/cleaners

c. Explosives – many nitrogen containing compounds (TNT)

d. HF – as glass etcher

I. Definitions

a. Allotropes – different forms of the same element (e.g. diamond and graphite for carbon)

b. Isomer – same formula, different arrangements (different bonds or different 3D- arrangement). Common in organic questions

c. Gravimetric – analysis by weighing

J. Trivial/Common names and household chemicals/applications

a. Caustic soda or (lye) – sodium hydroxide

b. Lime – CaO or calcium hydroxide used to make acidic soil less acidic

c. Epsom Salts – magnesium sulfate used in bathing salts to relieve aches and pains.

d. Milk of magnesia – magnesium hydroxide as an antacid or laxative

The answer is ‘yes and no’, and it depends on how you count them. The relevant piece from the book is pictured below.

92?

1987, 1

1992, 6

2001, 3

2004B, 5

2005B, 1

2006B, 1

Equation 1:

Delta G STANDARD = – RT ln K

Since K is the equilibrium constant, we are AT equilibrium, the amounts of products and reactants in the mixture are fixed, and the SIGN of Delta G STANDARD can be thought of as a guide to the ratio of the amount of products to the amount of reactants at equilibrium, and should NOT be thought of as a predictor of the feasibility of the reaction.

IF it so happens that products and reactants are equally favored at equilibrium, then Delta G STANDARD is zero, BUT Delta G STANDARD is not *necessarily* ZERO at equilibrium (I think this is the key).

Equation 2:

Delta G = Delta G STANDARD + RT ln Q

Since Q is NOT the K, and we are NOT necessarily at the equilibrium position, the SIGN of Delta G can be thought of as a prediction about which way the reaction (that has reactants and products defined by Q), will go.

If Delta G STANDARD is negative at equilibrium, then we will have lots of products at equilibrium, meaning Q  needs to be big (greater than 1). As Q gets larger (i.e. as we get more products), the term ‘RT ln Q’ gets increasingly positive and eventually adding IT to a negative Delta G STANDARD will make Delta G = 0 and equilibrium will be established and no further change occurs.

It is possible that Q could already be too large and therefore Delta G is positive. IF so, then the reaction will need to from more reactants, reduce the value of Q, and allow Delta G to reach zero, i.e. allow equilibrium to be established.

If Delta G STANDARD is positive at equilibrium, then we will have lots of reactants at equilibrium, meaning Q needs to be small (i.e. less than 1). As Q gets smaller (i.e. as we get more reactants), the term ‘RT ln Q’ gets increasingly negative and eventually adding IT to a positive Delta G STANDARD will make Delta G = 0 and equilibrium will be established and no further change occurs.

It is possible that Q could already be too small and therefore Delta G is negative, IF so, then the reaction will need more products, decrease the value of Q, and allow Delta G to reach zero, i.e. allow equilibrium to be established.

IN short, it is Delta G (NOT Delta G STANDARD) that will be zero at equilibrium and the sign of IT (in combination with Delta G STANDARD and RT ln Q in Equation #2.), will define which way the reaction proceeds.

As usual, when studying Thermodynamics with my AP classes, I did a lab that involves a couple of reactions; one endothermic and one exothermic followed by the application of q = m c Delta T. The calculations associated with this lab and these reactions are very messy in two ways. Firstly the problem of deciding what actually constitutes ‘m’ in the equations is tricky. Gases are given off, single replacement reactions lead to the depositing of solids and reactants are in excess – what do we add together to get the correct ‘m’? Secondly, the problem of assigning signs correctly in order to end up with a positive sign for the endothermic reaction and a negative sign for the exothermic reaction is a prickly one. Most texts make much too difficult a song and dance about this IMO, and frankly you often run into the sign convention problem.

Frankly, the ‘mass issue’ is really a non-issue when it comes to the AP exam (as explained at the end of the document below), but the sign issue has the potential to be much less easy to clean up. This year, for the first time, I decided to create a short document that attempts to clarify things once and for all – I think it worked very well, and it seemed to be the clearest for the kids in many years.

This time, the German language version (Wie man aus 92 Elementen ein ganzes Universum macht) won the Junior section of the ‘Wissenschaftsbuch des Jahres’, a prestigious literary award presented in Austria.

German language version of '92'

Literally translated, “Wissenschaftsbuch des Jahres’ means, ‘science/research/scholarship book of the year’, although in contemporary German language (my limited knowledge suggests that) the word ‘Wissenschaft’ often simply means ‘science’. Having said that, given that there are three other categories (Science/Technology, Medicine/Health and Social/Cultural Studies) it does suggest that the word has a slightly wider meaning than simply ‘science’ – anyway, probably more information than you need to know.

The award was the brainchild of Johannes Hahn the former Austrian Minister For Science and Research, and the current European Commissioner for Regional Policy, and is presented by the Austrian Minister for Science, Karl Heinz Töchterle, in association with the Austrian Ministry for Science.

The award ceremony is in Vienna in February and I am hoping to be able to attend since amongst other things, I might get to meet one of the other winners, Bill Bryson!

There’s a little more information here.

You may know that the UoN has made a great collection of short, vignette videos telling you something about each element on the periodic table, and this set of QR codes (that you scan with your smartphone) will take you to the You Tube clip for the element.

UoN QR Codes

Here’s a quick clip explaining it.