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A major challenge in implementing the hydrogen economy is
Chapter , Problem 8.88(choose chapter or problem)
A major challenge in implementing the "hydrogen economy" is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, \(\mathrm{NaAlH}_{4}\) can release \(5.6 \%\) of its mass as \(\mathrm{H}_{2}\) upon decomposing to \(\mathrm{NaH}(s), \mathrm{Al}(s)\), and \(\mathrm{H}_{2}(g)\). \(\mathrm{NaAlH}_{4}\) possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (a) Write a balanced equation for the decomposition of \(\mathrm{NaAlH}_{4}\). (b) Which element in \(\mathrm{NaAlH}_{4}\) is the most electronegative? Which one is the least electronegative? (c) Based on electronegativity differences, predict the identity of the polyatomic anion. Draw a Lewis structure for this ion. (d) What is the formal charge on hydrogen in the polyatomic ion?
Questions & Answers
QUESTION:
A major challenge in implementing the "hydrogen economy" is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, \(\mathrm{NaAlH}_{4}\) can release \(5.6 \%\) of its mass as \(\mathrm{H}_{2}\) upon decomposing to \(\mathrm{NaH}(s), \mathrm{Al}(s)\), and \(\mathrm{H}_{2}(g)\). \(\mathrm{NaAlH}_{4}\) possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (a) Write a balanced equation for the decomposition of \(\mathrm{NaAlH}_{4}\). (b) Which element in \(\mathrm{NaAlH}_{4}\) is the most electronegative? Which one is the least electronegative? (c) Based on electronegativity differences, predict the identity of the polyatomic anion. Draw a Lewis structure for this ion. (d) What is the formal charge on hydrogen in the polyatomic ion?
ANSWER:Step 1 of 4
(a)
The name is \(\mathrm{Na} \mathrm{AlH}_{4}\) sodium aluminum hydride.
The decomposition of the sodium aluminium hydride occurs in two steps.
The chemical reactions of decomposition are as follows.
\(\begin{aligned}3 \mathrm{NaAlH}_{4} \rightarrow \mathrm{Na}_{3}\mathrm{AlH}_{6}+\mathrm{Al}+\mathrm{H}_{2} \\\mathrm{Na}_{3} \mathrm{AlH}_{6} \rightarrow 3 \mathrm{NaH}+\mathrm{Al}+\frac{3}{2} \mathrm{H}_{2}\end{aligned}\)