electrolyte is one that ionizes completely or nearly completely, and a weak electrolyte doesn’t
ionize very much at all. Examples of strong electrolytes are NaCl, KCl, HCl, HBr, and HI.
Examples of weak electrolytes are water, HF, acetic acid, benzoic acid, and ammonia.27 . E
If an element loses an electron, it will have more protons than electrons and with this stronger
positive charge can pull the electrons in closer. Therefore, its ionic radius would be less than
its atomic radius. Thus, Na, K, Mg, and Ca will all lose electrons and become smaller. Cl, on the
other hand, will gain an electron; its positive nucleus cannot hold on to that extra electron as
tightly, and its ionic radius is larger than its atomic radius.
28 . A
A crystal is a solid whose atom, ions, or molecules are arranged in a regular 3D lattice
structure. The basic repeating structure is known as the unit cell.
29 . C
The oxidation state of nitrogen in N 2 is 0. In N 2 O it is +1, in NH 3 it is –3, in NO 2 it is +4, and in NO 3
it is +6. Oxygen is typically –2 and H is usually +1. Therefore, NH 3 is the correct answer.
30 . C
In order to answer this question correctly, you need to know the first law of thermodynamics:
The change in internal energy, ∆E, equals the amount of heat transferred, q, minus the
amount of work transferred, w. If heat is added to the system, q is positive; if it is transferred to
the surrounding, it is negative. If work is done by the system, w is positive; if work is done on
the system, w is negative. In this example, 500 joules of heat is added to the system, so q is
equal to 500 joules. The system does 75 joules of work on the surrounding, so w is equal to 75
joules. Plugging these into our equation, the change in internal is equal to 500 minus 75, or
425 joules.
31 . A
NaOH and H 2 SO 4 (a strong base and a strong acid) both dissociate completely in H 2 O into their
ionic components Na+, OH–, 2H+, and SO 4 2–, which then form a salt and water. The driving force
of this double displacement reaction is the formation of water by the OH– and H+ ions.
32 . D
To answer this question, you simply need to know the definition of ground state and excited