38 . C
5 g NaOH/40 g/mol = 0.125 mol NaOH and therefore 0.125 mole of OH–. You must have 0.125
mole of H+ ions to neutralize your OH– ions.0.25 N HCl; in this case N = M so you have 0.25 M HCl.0.25 mol/L; you need 0.125 mol. How many mL will have 0.125 mol in it?0.125 mol/0.25 mol/L = 0.5 L or 500 mL.Recall that N (normality) is equal to the molarity of the substance of interest for the reaction.
In this case, the molarity of H+ is what we’re concerned with.39 . D
40 . B
To answer questions about a molecule’s polarity, you must think about the geometry of the
molecule as well as the polarity of the individual bonds. Of the molecules given in the choices,
all but choice B are symmetrical and so, even if their bonds are polar, the molecules
themselves will not have a dipole moment. According to the valence shell electron-pair
repulsion theory, the three N-F bonds in NF 3 point toward the vertices of a tetrahedron and
the nitrogen’s lone pair of electrons points toward the fourth vertex, so the molecule has a
trigonal pyramidal conformation. The NF 3 molecule is thus asymmetrical and will have a net
dipole moment. The electronegativity difference between nitrogen and fluorine shows that
fluorine exerts a greater pull on the electrons in the NF bonds, so the dipole moment will put a
partial negative charge on the fluorine end of the molecule and a partial positive charge on the
nitrogen, despite its lone pair of electrons.41 . C
The first thing that you need to do to answer this question correctly is to construct the
equilibrium constant expression. The equilibrium constant expression for this reaction is the
concentration of hydrogen bromide squared over the product of the hydrogen concentration