Tuition Centre Singapore A Level Chemistry Tuition – Chemical Bonding

• Posted on admin
• in Blog
• on January 9, 2016
• No Comments.

Tuition Centre Singapore A Level Chemistry Tuition – Chemical Bonding

LiAlH4 and NaBH4 are used as a source of hydride ions, H–, in many organic reactions. Both chemical formulae consist of a metal cation and an anion made up of a group of atoms.

Solid LiAlH4 decomposes upon heating to 150 °C while solid NaBH4 melts at a temperature of 400 °C.

Which one of the following statements about LiAlH4 and NaBH4 is correct?

A      The H– from LiAlH4 is more available for donation due to the higher polarity of the Al–H bond compared to B–H bond in NaBH4.

B      The release of H– from LiAlH4 and NaBH4 involves homolytic fission of a covalent bond.

C      The lower stability of LiAlH4 to heat can be explained by the higher charge density of the cation and anion present compared to NaBH4.

D      The presence of a distinct melting point for NaBH4 means that the covalent bonds in the anions are weaker than the ionic bonds between the cations and anions.

Answer : A

Please contact Mr Ong @ 9863 9633 or Angie @ 96790479 if you need help in JC/A lvel H2/H1 Chemistry Tuition