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CHEM 1001
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Final Examination December 2012CHEM 1001 A and TR BurkPage 1 of 13Part A Answer all twelve questions with a few sentences or equations 5 marks each1 State the Pauli exclusion principleThe Pauli exclusion principle states that no two electrons in an atom can have the same four quantum numbers 2 Beginning with NiS show the reactions leading to acid rain ie HSO s24aqNiS15 ONiOSOs2gs2gSO OSO2g2g3gSOHOHSO3g2g24aq3If a sample of gas is compressed and heated is DE positive or negative WhyDEqw In this case both q and w are positive therefore DE is also positive4 Which has the larger lattice energy RbBr or CsBr WhyssThe lattice energy of RbBr is greater The only difference is the size of the cation The Rb ion is smaller than the Cs ion Therefore the Rb is closer to the Br than is the Cs resulting in a larger force of attraction between Rband Br thus the larger lattice energy of RbBr5 Why are metals not transparentIn a metal the bandgap is small Thus photons of almost any energy in the visible portion of the spectrum are easily absorbed exciting electrons from the HOMO to the LUMO These visible photons are therefore not transmitted by substance causing it to be opaque not transparent6 What type of hybrid orbitals are being used by the indicated atoms in the structure of aspartic acid shown below21233221 sp2 sp3 sp4 sp5 sp5437 Is AsF a polar molecule Why or why not3It is polar If we draw the Lewis structure we see that it has a lone pair on the As atom Thus it has a trigonal pyramidal shape and the dipole moment will not be zero because As and F have different electronegativities8Which will have the lowest freezing point 10 m NaCl 10 m NaSO or 05 m AlCl 4aqaq23aqWhyFreezing point depression is a colligative property and therefore depends on the amount of solute in solution 10 m NaCl is actually 20 m in ions 10 m NaSO is 30 m in ions and 05 m aq24aqAlCl is 20 m in ions Thus 10 m NaSO will have the lowest freezing point3aq24aqFinal Examination December 2012CHEM 1001 A and TR BurkPage 2 of 139VSEPR would predict the shape of XeF to be square planar In fact it is a square pyramid Why4This molecule has 35 valence electrons The four single bonds and completed octets on the F atoms use 32 of these leaving three more electrons to go on the central Xe at as a lone pair and a single electron The lone pair repels the bonding pairs more strongly than does the lone electron pushing the F atoms together slightly resulting in a square pyramidal shape10Why are unsaturated compounds often very reactiveUnsaturated molecules have multiple CC bonds Some of these bonds are bonds Electrons in bonds are delocalized and further from the CC bond axis than the electrons and therefore are easier to remove for instance by an oxidant11The phase diagram for carbon is shown below Which is more dense diamond or graphite How do you knowDiamond is more dense We know this because it exists at higher pressure than graphite Materials at higher pressure must have higher densities12Shown below is the amino acid alanine Is alanine chiral or achiral How do you know The indicated carbon atom has four different groups bonded to it CH NHCOOH and H 32Thus the molecule is chiral
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