Question

1. which member of each pair is more soluble in water? why?

(a) ( mathrm{ch}_{3} mathrm{ch}_{2} mathrm{och}_{2} mathrm{ch}_{3}(1) ) or ( mathrm{ch}_{3} mathrm{ch}_{2} mathrm{och}_{3}(g) )
(b)
cyclohexane
or
tetrahydropyran
(c) ( mathrm{ch}_{2} mathrm{cl}_{2}(1) ) or ( mathrm{ccl}_{4}(1) )

Explanation:

• (a)
• Water is a polar solvent. The solubility of a compound in water depends on its polarity and ability to form hydrogen bonds.
• \(CH_3CH_2OCH_2CH_3\) (diethyl ether) has a non - polar ethyl groups \((CH_3CH_2 -)\) attached to the oxygen. \(CH_3CH_2OCH_3\) (methyl ethyl ether) has a smaller non - polar group (\(CH_3-\) compared to \(CH_3CH_2-\)).
• The smaller non - polar group in \(CH_3CH_2OCH_3\) makes the molecule more polar overall (since the oxygen's polarizing effect is less shielded by a smaller non - polar group). Also, \(CH_3CH_2OCH_3\) can form hydrogen bonds with water (through the oxygen atom) more effectively as the non - polar part is less bulky.
• (b)
• Tetrahydropyran has an oxygen atom. The oxygen can act as a hydrogen bond acceptor with water molecules (\(H - O - H\) in water).
• Cyclohexane is a non - polar hydrocarbon (contains only \(C - C\) and \(C - H\) bonds). Non - polar hydrocarbons do not form hydrogen bonds with water and are not soluble in water due to the “like dissolves like” principle (water is polar, cyclohexane is non - polar).
• (c)
• \(CH_2Cl_2\) (dichloromethane) has a net dipole moment. The \(C - Cl\) bonds are polar (\(Cl\) is more electronegative than \(C\)).
• \(CCl_4\) (carbon tetrachloride) has a symmetrical tetrahedral structure. The individual \(C - Cl\) bond dipoles cancel each other out (\(\mu = 0\)).
• Water is polar. A polar solvent (water) will dissolve a more polar solute better. Since \(CH_2Cl_2\) is polar (\(\mu

eq0\)) and \(CCl_4\) is non - polar (\(\mu = 0\)), \(CH_2Cl_2\) is more soluble in water.

Answer:

• (a) \(CH_3CH_2OCH_3\) is more soluble in water. It has a smaller non - polar group, making it more polar and better at forming hydrogen bonds with water.
• (b) Tetrahydropyran is more soluble in water. It has an oxygen atom that can act as a hydrogen bond acceptor, while cyclohexane is non - polar.
• (c) \(CH_2Cl_2\) is more soluble in water. \(CH_2Cl_2\) is polar (\(\mu

eq0\)), and \(CCl_4\) is non - polar (\(\mu = 0\)), and water (a polar solvent) dissolves polar solutes better.