Question

1. What would you expect the observed boiling point to be at 10 torrs of a liquid which has a boiling point of 300 °C at 760 torrs? (Use Figure)
2. Would it be possible to establish the composition of an unknown binary mixture of two substances from mixture melting-point data? Explain.
3. After recording the R values using as a solvent system ethyl acetate and hexane (1:4), determine what solvent system is needed to obtain values between 0.3-0.4 for each of the following systems: benzaldehyde, 4-chlorobenzaldehyde, and cyclohexanol.
4. Using as a solvent system ethyl acetate and hexane (1:4), predict which compound from the following set would have .higher Rf value: (a) cyclo-hexanol and cyclohexane, (b) benzoic acid and benzaldehyde, and (c) caffeine and naphthalene.
5. The melting point of pure trans-cinnamic acid is 133 °C, and that of 2-acetoxybenzoic acid (aspirin) is 135 °C (Appendix A, Table 9W.2). Given pure reference standards of both acids, describe a melting-point procedure by which you could identify whether an unknown sample melting in this range could be assigned to either structure or to neither one.

Answer 1

Question 1.

According to Gay-Lussac's law:

The pressure of the gas is directly related to its absolute temperature.

i.e. P1/T1 = P2/T2

Where P1 is the pressure of the gas at an absolute temperature T1.

P2 is the pressure of the gas at an absolute temperature T2.

760 torr/(300+273.15) K = 10 torr/T2

i.e. T2 = 7.54 K

i.e. T2 = (7.54 - 273.15) ^oC = -265.61 ^oC