Question

1. After my solubility experiment, I got these results:

D-glucose and benzoic acid were dissolved in NaOH while sodium benzoate, 2-naphthol, and ethanol were not dissolved in NaOH.

Are the results correspond to theoretical results? And also, what are the reasons for each solute's solubility in NaOH? (i need a justification)

2. During the experiment, I dissolved an unknown compound in five different solvents including water, diethyl ether, aqueous HCl, aqueous NaOH, and aqueous NaHCO3. The results were:

Unknown	Water	Diethyl ether	Aq. HCl	Aq. NaOH	Aq. NaHCO3
Solubility behavior	soluble	insoluble	soluble	soluble	soluble

Based on these results, what does it tell you about the unknown's structure, functionality, and capacity for intermolecular interactions?

Answer 1

It's an excellent question.

1) D-glucose and benzoic acid were dissolved in NaOH because

a) benzoic acid has -COOH group which reacts with NaOH to form Sodium benzoate + water, hence it is a typical acid-base reaction resulting into salt formation and water. Since Sodium benzoate is ionic compound, it is soluble in water. Thus due to interactions between ions Na+ and COO- with water, it becomes soluble.

b) D-glucose is simply soluble in water due formation of hydrogen bonds with water. D-glucose has -OH group and C=O group which can easily form hydrogen bonding leading to solubility.

Sodium benzoate, 2-naphthol, and ethanol were not dissolved in NaOH.

Reason: Sodium benzoate is already a salt and must be soluble in NaOH solution. So, your results are inaccurate and does not match with theoretical explanation.

2-naphthol has an -OH group which can react with NaOH solution to form hydrogen bonds which will hence be soluble. Again the experimental data collected does not match with theoretical results.

Ethanol is a solvent and a solvent cannot dissolve in another solvent. The two solutions in liquid state can be miscible with each other. Moreover, NaOH solution must be miscible with Etahnol.

2) Based upon the results, it can be judged that the unknown compound is acidic in nature and also has some polarity
Reasons:
a) Water solubility means it must be polar that can be due to polar groups (hydrogen bonding can be present) or ion formation
b) Diethyl ether insoluble means it does not interact with mildly polar solvent indicating the strong polar nature.
c) Aq. HCl: solubility means that the unknown compound interacts with water due to hydrogen bonding or ion-solvent pair formation
d) Aq. NaOH:olubility means that the unknown compound interacts with water due to salt formation or hydrogen bonding
e) Aq. NaHCO3:olubility means that the unknown compound interacts with water due to salt formation or hydrogen bonding

Thanks for posting

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