solids that possess an active metal (an element from the s region). These
compounds appear white (for instance, NaCl or table salt). Choice (D) is
rust, which is not blue. CuSO 4 contains the transition metal copper (Cu),
and its crystals are bright blue.
- D Remember: The atomic weight of an element is the weighted average of
all the different isotopes an element exists in. If 50 percent of element X
had a mass of 210 amu and 50 percent had a mass of 214 amu, the
weighted average would be 212 amu. Notice that we are told element X
exists as ^214 X more than half of the time. So the answer must exceed 212.
However, since element X also exists in an isotope with a mass less than
214, we expect that its atomic weight is less than 214 amu. Only (D) has
a mass greater than 212 amu and less than 214 amu.
- B The container holds a total of 6 moles of gas. Oxygen (O 2 ) constitutes
one-third of that content. If you know how to work partial pressure
problems, you know that oxygen’s contribution to the total 760 torr of
pressure is one-third. 760 torr/3 = approximately 253 torr.
- D Since we’re considering the dissolution of an ionic solid into water, we
need to consider the solubility product expression. The solubility product
constant, Ksp, will equal the product of aqueous ion concentrations raised
to their coefficients. (Remember that solids are not expressed.) This is the
relationship expressed in choice (D).
- D The normal electron configuration for magnesium would be
1 s^22 s^22 p^63 s^2 . Since we’re talking about an “excited” magnesium atom in
which one electron has been pushed up into a higher energy state, we’re
looking for a configuration that shows one electron in a higher state than
it should be. The total number of electrons should still be equal to
magnesium’s atomic number, but the location of one electron should be
“elevated.”
Choice (D) is just what we’re looking for. Total number of
electrons? Twelve, just as it should be. But look at the last
entry. Instead of 3s^2 , we see 3s^13 p^1 . The last electron has
been elevated to the 3p subshell.
- A To form an electrolytic solution, the solute must dissociate into ions.
