Monday, May 18, 2015

How to Optimize True False questions on SAT II Chemistry Subject Test


In order to get a perfect 800 score on the SAT II Subject Test in Chemistry, the True-False section is the most unique and the most difficult for many students. In addition to the standard way to handle True-False questions, you must also bubble CE afterward if both statements are true and the second one would cause the first statement. A great strategy is to read both statements as one statement with a because between them in order to evaluate whether the combined statement is CE. Something can only be CE if both statement are true but they do not have to be CE. "True, True and not CE" is a possibility if there is no connection between the statements.

The True-False questions on the SAT II Subject Test in Chemistry start at number 101 on your answer sheet but are really about the 20th question in the test, right after the word bank problems. Don't be alarmed that start on number 101, you didn't miss any questions.There is no break between sections so you must keep track and optimize your time to tell if you need to speed up or have time to read questions more thoroughly.
Typically about fifteen True-False questions with two statements and evaluating the CE so this is the equivalent of between 30 and 45 questions. You need to be fairly quick on this section to answer the other 70 questions of so correct in the allotted hour (as outlined in the SAT and AP Chemistry exam format differences) so it would be great to finish these questions in about 10 minutes. It is not a bad idea to save these until the end although they are not very time consuming. You essentially have to get all 3 questions of each set correct in order to get credit for that question. There is no partial credit. If you get any part wrong, you lose a quarter of a point. Since probabilities on compound events are multiplicative, being slightly unsure about any one statement can dramatically increase the chance that you are incorrect in total.

Since you do not need to get everything correct on SAT II Subject Test in Chemistry test for an 800, you may want to skip some questions that you are completely unsure in order to optimize your score. You don't lose any points for skipping but lose a quarter of a point for an incorrect answer on the True False section, equivalent to each question on any other section. Since there is so little time for so many questions, the worst thing you can do is spend a lot of time on any one question and still get it wrong. Depending on the pool of students taking the test, you can get about two wrong or leave a couple more blank and still get an 800. Have a plan on deciding what types of questions you want to leave blank or skip until the end if you have time. Don't waste precious time deciding that during your test. Ideally, you want to be prepared and confidently execute your strategy on each type of problem as you see it.

The SAT Subject Test in Chemistry True False questions typically include definitions or properties that can be memorized or figured out based on understanding some common phrases and ideas, which overlap heavily with the AP Chemistry Exam and Regents Chemistry Exam. Important topics highly covered in the True False questions include properties of the nucleus and electrons, periodic trends, molecular geometry of common molecules and how that affects polarity, intermolecular forces, phase changes, and solubility rules. Formulae for organic molecules and spotting functional groups (some reactions as well) are important. Conservation of mass, energy, and charge is usually tested as well as other thermodynamics such as Gibb's Free Energy and its relationship to entropy, enthalpy, and the formation of bonds. Names and properties of common compounds as well as real world laboratory knowledge is included - paying thorough attention in lab (and class of course!) throughout the year will greatly help. No ice charts or complex equilibria and there is very little stoichiometry or anything else math related )like ideal gas laws or energy through a temperature or phase change). If they do ask something math-based on these, they are usually much simpler than the rest of the test and should be a quick mental calculation.

There is typically little math on these types of questions so some statements can be slightly ambiguous. Invariably, there will be at least a couple of questions in which you are unsure. If you can evaluate at least one of the statements, you can increase your percentage to get it correct and minimize your chance to get it wrong by checking if there is a relationship between the two.

You may be tempted to conclude that each has a 20% chance to be the correct answer, but each probability is not equal. Here is how I calculated the probability of any one choice. You do not need to understand this in order to apply the principles that can be concluded from it so feel free to skip this part until the bullets below. Assume each statement is an independent event. The first statement has a 1 out of 2 (50% chance) to be True and 50% chance to be False. If the first statement was False, the second statement has a 50% chance to be True and a 50% chance to be False. Since the probability of independent events is multiplicative, there is a 25% chance ( 50% chance * 50% chance) to be "False, True" and a 25% chance to be "False, False." Similarly, there's a 25% chance to be "True, False" and a 25% chance that the first two statements are true. If the first statement is True and the second statement is True, there's a 50% chance that it can be CE and a 50% chance of not CE (just True, True). Therefore, True, True, CE has a 12.5% (50% of 25% from "True, True"). This is not necessarily the breakdown of the correct answers on the test, but it will allow us to make some better decisions when faced with questions about which we are unsure.

There are 5 different choices for each questions:
  • True, True, CE = Both statement are true and the second one causes the first one = 12.5% probability
  • True, True = Both statements are true but there is no relationships between them = 12.5% probability
  • True, False = The first statement is true and the second statement is false = 25% probability
  • False, True = The first statement is false and the second statement is true = 25% probability
  • False, False = Both statements are false = 25% probability

As you can see from the list above, if the first statement is True, the second statement can be True or False (equally as likely), but if True can be CE or not CE (equally as likely as each other). Therefore, the probability of "True, True, CE" + probability of  "True, True" = the probability of each of the other choices individually. We can use these probabilities to give us an extra edge when we are not sure.

A great strategy to optimize your score is when you are unsure is to look toward the second choice:
  1. When in doubt, choose "False, True" if you know the second statement is True and there is no relationship.
  2. Even if you are completely unsure about the validity of the second statement but know the second statement would prove the first one true if the second were true, the correct answer is likely "True, True, CE."
False, True example
If the second statement is True and you know there is no relationship, the second statement is likely False and the correct choice is likely "False, True".
Catalysts get denatured in a reaction.      A catalyst can reduce the activation energy of a reaction.
The second statement is definitely true as that is an important common idea but there is no relationship between reducing the activation energy and getting denatured so the correct answers is False, True.

True, True, CE example where the definitions are unknown
If the second statement is True and would prove the first statement, then the best answer is likely "True, True, CE."
First statement: A dogalyst's area can be calculated by squaring its radius and multiplying by pi.
Second statement: A dogalyst is a circle.
Let's assume that a dogalyst exists for the time being (it might but I tried to make up something that's nonsensical). If you came across this problem and had no clue about the first statement, look toward the second statement. Once again, the second statement is ambiguous but does reveal a relationship between the two statements. If the the second statement is true, it would prove the first statement. Circles can be calculated through the formula pi r^2. Therefore, the best answer on a test in a situation like this would be "True, True, CE."

True True, not CE example
A catalyst can speed up reaction           Catalysts are reusable
These actually exist and are common ideas that you should know for the SAT Chemistry. Catalysts do speed up reactions and they are reusable; however, they don't have much of a relationship between each other under most high school level conditions. Therefore, True, True and NOT CE is the best choice. You do not have to fill in NOT CE, just leave the CE bubble unfilled.

Pay attention to absolute words (I don't mean Kelvin temperature but those are important as well) like always and never. These are almost always false as there are usually exceptions in various situations. When in doubt, go with False.

Pay attention to qualifier words like sometimes, likely, often, can, or may. These may make many but not all statements true. Read everything as thoroughly as possible.

If you cannot apply any of the tips above and if you have never heard of it before, go with False unless you can show a relationship like above. If you have taken a high school chemistry class, have taken practice exams, and have a tutor, there is nothing that should be surprising.

Please share any other tips or tactics for acing the SAT II Subject Test in Chemistry in the comments below.

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