1. Cr crystalizes in a body centered cubic lattice with a cell constant of 287.2 pm. The atomic mass of Cr is 52.00 g·mol–1. Calculate the density in units of g·cm–3.
2. For each of the following pairs of acids, indicate the stronger acid and briefly explain your reasoning. a) [Fe(OH2)6]3+ or [Fe(OH2)6]2+; b) HClO3 or HClO4.
3. Will Ga doped into Ge be an n– or p–type semiconductor? Explain your reasoning.
4. Calculate the lattice energy for MgS (which crystallizes in the rock salt lattice) using the Born-Mayer equation and a Born-Haber cycle using the data given below. Do the two values agree, within experimental expectations? If not, provide a reason.
5. Consider methanol (CH3OH), acting as a Lewis acid, reacting with acetone (CH3(C=O)CH3) and DMSO (CH3(S=O)CH3). Find the enthalpy of each reaction. Based on these results, comment on the solubility of these liquids with each other.
Possibly useful information
NA = 6.022×1023 mol–1 4πεo = 1.113×10–10 J–1·C2·m–1 e = 1.602×10–19 C d* = 34.5 pm
A (rock salt) = 1.748 r+ (Mg2+) (CN = 6) = 72 pm r–(S2–) (CN = 6) = 184 pm
Elat = –[(NAAZ+Z–e2)/(4πεodo)] (1-d*/do) S(Mg(s)) = 148 kJ·mol–1 S(S(s)) = 277 kJ·mol–1
ΔfHo(MgS) = –347 kJ·mol–1 IE1(Mg) = 737 kJ·mol–1 IE2(Mg) = 1476 kJ·mol–1
EA1(S) = 2.00×102 kJ·mol–1 EA2(S) = –492 kJ·mol–1 BDE (S-S) = 264 kJ·mol–1
–ΔrHo = EAEB + CACB pKa1 ~ 8 – 5p pKa2 ~ pKa1 + 5
Compound E (kJ·mol–1)½ C (kJ·mol–1)½
CH3OH 6.980.296
CH3(C=O)CH3 2.024.67
CH3(S=O)CH3 2.765.83