Activity 15: Structural Effects on Solubility

Question 1

Driving force for solubility may be due to 3 factors:

Answer 1

1. solute-solvent intermolecular attractions - solubility in water and ether (litmus: blue, red, unchanged)
2. Chemical reaction - solubility in H2SO4
3. Acid-base reaction - solubility in HCl, NaOH, NaHCO3

Question 2

Indicate the driving force for the solubility of each of the following compound in its respective solvent (solute-solvent molecular force, acid-base reaction, chemical reaction):

1. aniline
2. benzaldehyde
3. acetic acid
4. diethyl amine
5. palmitic acid
6. n-hexane
7. phenol
8. 2-propanol
9. sucrose

Answer 2

1. acid-base reaction
2. chemical reaction
3. solute-solvent molecular force
4. solute-solvent molecular force
5. chemical reaction
6. not soluble in water nor acid
7. acid-base reaction
8. solute-solvent molecular force
9. solute-solvent molecular force

Question 3

What compound is soluble in NaOH but not in NaHC03. explain its solubility

Answer 3

Phenol. The difference in solubility between NaOH and NaHCO3 is primarily due to the difference in their basicity. NaOH is a strong base compared to NaHCO3, and when it reacts w/ phenol, it is able to deprotonate it leading to the formation of soluble species that can readily dissolve in the aqueous solution of NaOH

Question 4

Which is more acidic, ethanol or phenol? Explain depicting the pertinent structural effects

Answer 4

Phenol. phenoxide is stabilized by pi-electron delocalization of LP

Question 5

( acetic acid, monochloroacetic acid, trichloroacetic acid)
What is the trend in acidity. Explain depicting pertinent structural effects

Answer 5

acetic < monochloroacetic acid < trichloroacetic acid
chloro substituent makes the compound more acidic because it draws the electrons to itself by INDUCTIVE EFFECT, thereby decreasing the electron density of the carboxylate group

Question 6

Which is more basic, aniline or diethylamine? Explain depicting pertinent structural effects.

Answer 6

Diethylamine. Aliphatic amines are more basic than aniline due to DELOCALIZATION OF THE LONE PAIR of aniline towards the ring making it less available

Question 7

Acetylene

Answer 7

white precipitate

Question 8

benzene and heptane

Answer 8

no reaction ; no precipitate

Question 9

Write the equation for the reaction between AgCl and NH4OH.

Answer 9

AgCl + 2NH4OH → [Ag(NH3)2]Cl + 2H2O (silver ammonium chloride)

Question 10

For the test compound which gave a positive result, supply the equation of the reaction between it and silver ammonium chloride

Answer 10

lantaw sa notes ang answer

Question 11

In terms of structural effect, explain the reaction that took place above. Why is it that other test compound(s) did not give a positive result? Explain in detail. [3 points]

Answer 11

Only acetylene has acidic H due to orbital electronegativity of the Csp

Question 12

Predict the trend in increasing acidity of acetylene, benzene, and n-heptane. Explain this trend in terms of pertinent structural effects

Answer 12

n- heptane < benzene < acetylene

acetylene is the most acidic due its triple bond (sp) followed by benzene due its double bond (sp2) and n-heptane due to its single bond (sp3). The higher the s character in a bond, the more acidic it becomes