Cracking the SAT Chemistry Subject Test
CHAPTER 3 SOME BASIC STUFF
Drill 1
- A If you chose “mass” or “density” just because those words appeared
in the question, you fell for the temptation trap. The test writers wanted you
to do this. To answer this question correctly, you have to think carefully
about what the words mean, and you must not rush to an answer simply
because an answer choice contains a word that reminds you of something.
Let’s work through this. If you’re given a sample of
some substance, and you know the density of the
substance, what additional information would allow
you to calculate the mass? If you know its density, then
you know the ratio of mass/volume. Therefore, if you
were also provided with the sample’s volume, you
could figure out its mass. That’s why (A) is right.
- E You’re asked to determine which quantity or property always varies
with the number of molecules in a given sample of a substance. You have
the knowledge to answer this question, so don’t let the wording throw you.
Think about what you know; mass is a measure of the
quantity of matter. This means that for any sample of a
particular substance, mass always varies with the
number of molecules in the sample. More molecules of
substance X have a greater mass than fewer molecules
of substance X.
What about volume, temperature, density, and pressure?
Volume, (A), is a measure of the space a sample
occupies. The volume of a substance might vary as the
number of molecules of that substance is varied;
however, it does not have to change with the number of
molecules. This is certainly true in the case of gases: A
rigid container (with a fixed volume) may hold vastly
different amounts of the same gas because gases are
