91Ó°ÊÓ

Natural gas consists primarily of methane, \(\mathrm{CH}_{4}(\mathrm{~g})\). (a) Write a balanced chemical equation for the complete combustion of methane to produce \(\mathrm{CO}_{2}(g)\) as the only carbon-containing product. (b) Write a balanced chemical equation for the incomplete combustion of methane to produce \(\mathrm{CO}(\mathrm{g})\) as the only carbon-containing product. (c) At \(25^{\circ} \mathrm{C}\) and \(1.0 \mathrm{~atm}\) pressure, what is the minimum quantity of dry air needed to combust \(1.0 \mathrm{~L}\) of \(\mathrm{CH}_{4}(g)\) completely to \(\mathrm{CO}_{2}(g) ?\)

Nitrogen dioxide \(\left(\mathrm{NO}_{2}\right)\) is the only important gaseous species in the lower atmosphere that absorbs visible light. (a) Write the Lewis structure(s) for \(\mathrm{NO}_{2}\). (b) How does this structure account for the fact that \(\mathrm{NO}_{2}\) dimerizes to form \(\mathrm{N}_{2} \mathrm{O}_{4}\) ? Based on what you can find about this dimerization reaction in the text, would you expect to find the \(\mathrm{NO}_{2}\) that forms in an urban environment to be in the form of dimer? Explain. (c) What would you expect as products, if any, for the reaction of \(\mathrm{NO}_{2}\) with CO? (d) Would you expect \(\mathrm{NO}_{2}\) generated in an urban environment to migrate to the stratosphere? Explain.

The precipitation of \(\mathrm{A} \mathrm{L}(\mathrm{OH})_{3}\left(K_{\text {sp }}=1.3 \times 10^{-33}\right.\) ) is sometimes used to purify water. (a) Estimate the \(\mathrm{pH}\) at wh?ch precipitation of \(\mathrm{Al}(\mathrm{OH})_{3}\) will begin if \(5.0 \mathrm{lb}\) of \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) is added to \(2000 \mathrm{gal}\) of water. (b) Approximately how many pounds of \(\mathrm{CaO}\) must be added to the water to achieve this \(\mathrm{pH}\) ?