For each of the following pairs of solute and solvent, predict whether the solute would be…

Question

Question:

For each of the following pairs of solute and solvent, predict whether the solute would be…

Which of the molecules are polar? Check all that apply. BeCl2, CH3F, H2O, HF, CH4, NH3

For each of the following pairs of solute and solvent, predict whether the solute would be soluble or insoluble.

a) Malic acid in water.

b) Amphetamine in ethanol.

c) Succinic acid in hexane.

d) Naphthalene in water

Answer:

Solubility of Substances in Polar and Nonpolar Solvents:
The solubility of covalent compounds in various solvents is very much influenced by the presence or absence of polarity in the molecule and the balance of polar and nonpolar regions in the molecule. The old saying is “like dissolves like” meaning that polar molecules or substances are more likely to dissolve in polar solvents and nonpolar molecules in nonpolar solvents. The extent of these solubilities though are subject to other physical parameters not discussed here.

Explanation:
• a) Malic acid in water. – SOLUBLE
• b) Amphetamine in ethanol. – SOLUBLE
• c) Succinic acid in hexane. – INSOLUBLE
• d) Naphthalene in water. – INSOLUBLE

> a) Looking at the structure for malic acid, you can see that it is a dicarboxylic acid with an additional alcohol (hydroxyl) group present giving the molecule many polar sites and an overall molecular dipole making this a polar compound. Water is a polar solvent and would be able to dissolve malic acid.
> b) Amphetamine is a polar compound due to the amine group present, but there is also a large nonpolar region with the benzene ring, so the polarity of the molecule is moderate as it has both polar and nonpolar regions. Ethanol being a polar solvent with a some nonpolar character also will make a good solvent for this substance. The salt form, amphetamine sulfate, will be even more soluble in polar solvent as the amine will be protonated to a substituted ammonium cation and a sulfate anion.
> c) Succinic acid has the same structure as malic acid less the hydroxyl group, but it is still a polar compound. Hexane though is a nonpolar solvent and not likely to dissolve succinic acid.
> d) Naphthalene is a double benzene ring system and nonpolar in character. With water being a polar solvent, it will have difficulty dissolving this compound.

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