Chapter 11, Problem 32
The generic structural formula for a 1-alkyl-3-methylimid- azolium cation is where R is a -CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between 1-alkyl-3-methylimidazolium cation and the PF6- anion are as follows: R = CH2CH3 (m.p. = 60 °C), R = CH2CH2CH3 (m.p. = 40 °C), r = CH2CH2CH2CH3 (m.p. = 10 °C), and R = CH2CH2CH2CH2CH2CH3 (m.p. = -61 °C). Why does the melting point decrease as the length of alkyl group increases?
Video transcript
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (a) Explain why replacement of a hydrogen on the oxygen by a CH3 group generally results in a lower boiling point.
Based on the type or types of intermolecular forces, predict the substance in each pair that has the higher boiling point: (d) phosgene (Cl2CO) or formaldehyde (H2CO)
A number of salts containing the tetrahedral polyatomic anion, BF4-, are ionic liquids, whereas salts containing the somewhat larger tetrahedral ion SO42- do not form ionic liquids. Explain this observation.
(b) What is the relationship between viscosity and temperature?
Based on their composition and structure, list CH2Cl2, CH3CH2CH3, and CH3CH2OH in order of (c) increasing surface tension
Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:
(b) Which of these diagrams, i or ii, rep- resents what happens when water is on a nonpolar surface?