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Sodium and its Compounds

2018 Paper One

Question Eight
This question has a 16 mark value.

1. wrong terminology, for example wrong bonding and/or intermolecular forces in all/some of the substances, and showed contradictions in answers.
2.  Equation was often seen with sodium oxide as the product rather than sodium hydroxide. Many students did not use the 2:1 ratio from the equation.
3.  Most common error was to multiply the amount, in moles, by volume rather than dividing by volume.
4.  The structure often had the wrong number of lone pairs and/or the wrong bond angle.

Indicative chemistry content.

Contradictions (eg molecules, IMFs, covalent bonding,) negate statements.

Stage 1- Na
1a) Na has metallic bonding
1b) there is attraction/ bonding between the positive nucleus/ ion and the delocalised electrons in Na
1c) Na has a giant/lattice structure

Stage 2 – NaBr or NaI
2a) Ionic bonding in NaBr and/or NaI
2b) There is attraction/ bonding between the + and – ions in NaBr and/or NaI
2c) NaBr and/or NaI have a giant/lattice structure

Stage 3 - comparison of bonding
3a) The ionic bonds are stronger (or wtte) than the metallic bonds
3b) there is stronger attraction (or wtte) between the + and – ions in NaBr than in NaI
3c) since the Br – ion is smaller than the I– ion

Full marks are awarded only if all three Stages are covered
Make sure you are familiar with chemical terminology

moles of Na = 0.250/23.0 = 0.0109
moles of hydrogen = 0.0109/2 = 0.00545
temperature = 25 + 273 = 298 K
101 kPa = 101 000 Pa

Use PV = nRT (remember volume is in cubic metres)
V = (nRT)/P = (0.00545 x 8.31 x 298)/101 000 = 0.000134 cubic metres
Volume is 134 cubic centimetres

Concentration of sodium ions = 0.0109/0.5 = 0.0218 (mol dm-3)


The 4 electron pairs repel so are as far apart as possible
Lone pairs repel more than bonding pairs: lp/lp repulsion> lp/bp repulsion > bp/bp repulsion.

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