Problem 4
Write equations for the following processes, involved in the extraction of the elements from their ores: (a) the reduction of boron oxide by \(\mathrm{Mg}\) (b) the result of the addition of hot aqueous \(\mathrm{NaOH}\) to a mixture of solid \(\mathrm{Al}_{2} \mathrm{O}_{3}\) and \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) (c) the reaction of \(\mathrm{CO}_{2}\) with aqueous \(\mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_{4}\right]\)
Problem 7
Explain how, during dimerization, each \(\mathrm{BH}_{3}\) molecule acts as both a Lewis base and a Lewis acid.
Problem 9
The ordering of the relative stabilities of adducts \(\mathrm{L} \cdot \mathrm{BH}_{3}\) for some common adducts is, according to L: \(\mathrm{Me}_{2} \mathrm{O}<\mathrm{THF}<\mathrm{Me}_{2} \mathrm{S}<\mathrm{Me}_{3} \mathrm{N}<\mathrm{Me}_{3} \mathrm{P}<\mathrm{H}^{-}\). In addition to answering each of the following, indicate how you could use NMR spectroscopy to confirm your proposals. (a) What happens when \(\mathrm{Me}_{3} \mathrm{N}\) is added to a THF solution of THF.BH \(_{3}\) ? (b) Will \(\mathrm{Me}_{2} \mathrm{O}\) displace \(\mathrm{Me}_{3} \mathrm{P}\) from \(\mathrm{Me}_{3} \mathrm{P} \cdot \mathrm{BH}_{3} ?\) (c) Is \(\left[\mathrm{BH}_{4}\right]^{-}\) stable in THF solution with respect to a displacement reaction? (d) Suggest what may be formed when \(\mathrm{Ph}_{2} \mathrm{PCH}_{2} \mathrm{CH}_{2} \mathrm{PPh}_{2}\) is added to a THF solution of THF. \(\mathrm{BH}_{3},\) the latter remaining in excess.
Problem 14
Suggest likely products for the following reactions: (a) \(\mathrm{BCl}_{3}+\mathrm{EtOH} \rightarrow\) (b) \(\mathrm{BF}_{3}+\mathrm{EtOH} \rightarrow\) (c) \(\mathrm{BCl}_{3}+\mathrm{PhNH}_{2} \rightarrow\) (d) \(\mathrm{BF}_{3}+\mathrm{KF} \rightarrow\)
Problem 15
(a) Write down the formula of cryolite. (b) Write down the formula of perovskite. (c) Cryolite is described as possessing a 3 -dimensional structure closely related to that of perovskite. Suggest how this is possible when the stoichiometries of the two compounds do not appear to be compatible.
Problem 20
(a) The behaviour of \(\mathrm{H}_{3} \mathrm{BO}_{3}\) in aqueous solution is not typical of a mineral acid such as \(\mathrm{HCl}\) or \(\mathrm{H}_{2} \mathrm{SO}_{4}\). Illustrate, using appropriate examples, these differing behaviours. (b) The formula of borax is sometimes written as \(\mathrm{Na}_{2} \mathrm{B}_{4} \mathrm{O}_{7} \cdot 10 \mathrm{H}_{2} \mathrm{O} .\) Comment critically on this representation.
Problem 21
Compare the physical and chemical properties of \(\alpha\) - and \(\gamma\) -alumina, choosing examples that highlight why it is important not to call \(\mathrm{Al}_{2} \mathrm{O}_{3}\) simply 'alumina'
Problem 22
(a) Suggest products for the following reactions. $$3 \mathrm{EtB}(\mathrm{OH})_{2} \stackrel{-3 \mathrm{H}_{2} \mathrm{O}}{\longrightarrow}$$ $$\mathrm{ClB}\left(\mathrm{NMe}_{2}\right)_{2} \stackrel{2 \mathrm{Na}}{\longrightarrow}$$ $$\mathrm{K}\left[\left(\mathrm{C}_{2} \mathrm{F}_{5}\right)_{3} \mathrm{BF}\right]+\mathrm{SbF}_{5} \rightarrow$$ (b) \(\operatorname{Ph} \mathrm{B}(\mathrm{OH})_{2}\) forms dimers in the solid state. Dimers further associate into a 3 -dimensional network. Describe how this assembly is likely to arise.
Problem 23
Write a brief account of the bonding and reactivity of borazine which emphasizes the ways in which this compound is similar or dissimilar to benzene.
Problem 25
\(\mathrm{GaCl}_{3}\) reacts with \(\mathrm{KP}(\mathrm{H}) \mathrm{Si}^{\mathrm{t}} \mathrm{Bu}_{3}(\text { equimolar amounts })\) to give \(\mathrm{KCl}\) and two isomers of a 4 -membered, cyclic compound which contains \(38.74 \% \mathrm{C}, 7.59 \% \mathrm{H}\) and \(19.06 \%\) Cl. Suggest the identity of the product, and draw structural diagrams to illustrate the isomerism.
