Adding HCl(g) to water will produce hydrochloric acid, which ionizes
into H+ and Cl− ions. Choices (C), (D), and (E) are all ionic solids, which
will break into mobile ions upon dissolution in water. When N 2 (g) is
dissolved into water, no ions are produced, and the resultant solution is
nonelectrolytic.
- C The double arrow indicates that the reaction is reversible. NH 4 + is a
reactant of the reverse reaction; if NH 4 + donates a proton to HCO 3 −, NH 3
and H 2 CO 3 are formed. Since NH 4 + donates an H+ ion (or proton) to
another substance, it acts as an acid according to the Bronsted-Lowry
definition.
- A Add the superscripts to get the total number of electrons in the species: 2
- 2 + 6 + 2 + 6 = 18. Which of the choices also has 18 electrons? A quick
check of the periodic table shows that a sulfur atom has 16 electrons.
Adding two more electrons gives the S2− ion a total of 18 electrons.
- B For a substance to be amphoteric, it must be able to donate and receive
an H+ ion. Eliminate (A) and (E)—these species don’t have an H+ ion to
donate. Choice (C), KOH, is a strong base. We wouldn’t expect it to ever
act as an acid. Likewise, HNO 3 (choice (D)) is a strong acid that we
would not expect to behave as a base. That leaves HSO 4 −. Notice that it
can act as an acid and become a sulfate ion, SO 4 2−, or act as a base and
become sulfuric acid, H 2 SO 4.
- E The ideal gas equation is PV = nRT. When the amount of gas does not
change, n becomes a constant, like R. A little algebra gives us =
nR. Since is equal to a constant, it will not change with time.
Consider that we are dealing with two points in time. At first, the gas has
a volume of 10 liters at 20°C or (293 K) and 750 mmHg. So here,
