Chapter 4

Methanol, ${\mathrm{CH}}_3\mathrm{OH}$, and hydrogen chloride, $\mathrm{HCl}$, are both molecular substances, yet an aqueous solution of methanol does not conduct an electrical current, whereas a solution of $\mathrm{HCl}$ does conduct. Account for this difference. [Section 4.1]

You are presented with three white solids, $A,B$, and $C$, which are glucose (a sugar substance), $\mathrm{NaOH}$, and AgBr. Solid A dissolves in water to form a conducting solution. B is not soluble in water. C dissolves in water to form a nonconducting solution. Identify $\mathrm{A},\mathrm{B}$, and $\mathrm{C}$. [Section 4.2]

We have seen that ions in aqueous solution are stabilized by the attractions between the ions and the water molecules. Why then do some pairs of ions in solution form precipitates? [Section 4.2]

Which of the following ions will always be a spectator ion in a precipitation reaction? (a) Cl", (b) ${\mathrm{NO}}_3^{-}$, (c) ${\mathrm{NH}}_4^{+},(\mathrm{d}){\mathrm{S}}^{2-},(\mathrm{e}){\mathrm{SO}}_4{}^{2-}$. Explain briefly. [Section 4.2]

The labels have fallen off two bottles, one containing $\mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2$ and the other containing $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2$. You have a bottle of dilute ${\mathrm{H}}_2{\mathrm{SO}}_4$. How could you use it to test a portion of each solution to identify which solution is which? [Section 4.2]

Explain how a redox reaction involves electrons in the same way that an acid- base reaction involves protons. [Sections $4.3$ and $4.4]$

When methanol, ${\mathrm{CH}}_3\mathrm{OH}$, is dissolved in water, a nonconducting solution results. When acetic acid, ${\mathrm{CH}}_3\mathrm{COOH}$, dissolves in water, the solution is weakly conducting and acidic in nature. Describe what happens upon dissolution in the two cases, and account for the different results.

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes, that is, as separated ions in solution. What properties of water facilitate this process?

What does it mean to say that ions are hydrated when an ionic substance dissolves in water?

Specify what ions are present in solution upon dissolving each of the following substances in water: a) ${\mathrm{ZnCl}}_2$, (b) ${\mathrm{HNO}}_3$ (c) ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$, (d) $\mathrm{Ca}(\mathrm{OH}{)}_2$.