Predict the solubility of ethyl 4-aminobenzoate in water, 1.0 M NaOH (aq), and 1.0 M HCl (aq). Explain your prediction thoroughly for full credit. If a chemical equation is necessary, draw on a paper and insert a picture here. also, are toluene and methanol miscible or immiscible and why?
The Correct Answer and Explanation is :
Solubility of Ethyl 4-Aminobenzoate in Water, 1.0 M NaOH, and 1.0 M HCl
Ethyl 4-aminobenzoate (also known as ethyl para-aminobenzoate) is an ester formed by the reaction of 4-aminobenzoic acid with ethanol. The structure contains both an ester functional group (-COOEt) and an amine group (-NH2).
- In Water: Ethyl 4-aminobenzoate is slightly soluble in water. The primary reason is that the amine group (-NH2) can form hydrogen bonds with water molecules. However, the ester group (-COOEt) is relatively non-polar and reduces the molecule’s overall water solubility. The ester functional group disrupts the hydrogen bonding capability of the amine group, making it less soluble than a simple amine or acid.
- In 1.0 M NaOH (aq): In basic conditions, the amine group (-NH2) can undergo protonation to form an ammonium ion (-NH3+). The protonated amine is much more hydrophilic due to the ionic nature of the ammonium ion, making it highly soluble in water and basic solutions. Since sodium hydroxide dissociates to form OH- ions, it will deprotonate the amine group, leading to the formation of an ammonium salt, which is soluble in aqueous NaOH. Chemical reaction in NaOH: Ethyl 4-aminobenzoate (neutral) + NaOH→Ethyl 4-aminobenzoate (anion) + H2O\text{Ethyl 4-aminobenzoate (neutral) + NaOH} \rightarrow \text{Ethyl 4-aminobenzoate (anion) + H2O}
- In 1.0 M HCl (aq): In acidic conditions, the amine group will accept a proton and become positively charged (NH3+). The salt formed between the protonated amine and chloride (Cl-) makes the compound more soluble in water, as the ionic compound is highly soluble in aqueous acids. Thus, ethyl 4-aminobenzoate will be more soluble in 1.0 M HCl than in water. Chemical reaction in HCl: Ethyl 4-aminobenzoate (neutral) + HCl→Ethyl 4-aminobenzoate (ammonium salt) + Cl-\text{Ethyl 4-aminobenzoate (neutral) + HCl} \rightarrow \text{Ethyl 4-aminobenzoate (ammonium salt) + Cl-}
Toluene and Methanol: Miscible or Immiscible?
Toluene and methanol are miscible in all proportions. Here’s why:
- Methanol (CH3OH) is a small, highly polar molecule with an -OH (hydroxyl) group that can form hydrogen bonds with water or other alcohols. Methanol is capable of hydrogen bonding due to the presence of the hydroxyl group, making it a highly polar solvent.
- Toluene (C6H5CH3) is a non-polar aromatic hydrocarbon, meaning it has no significant dipole moment and doesn’t form hydrogen bonds.
Even though toluene is non-polar and methanol is polar, they are still miscible because methanol is strongly polar and capable of forming dipole-dipole interactions with the electron-rich aromatic ring of toluene. The relatively small molecular size of methanol and its ability to solvate non-polar molecules also contribute to their miscibility.
The key factor here is hydrogen bonding. The hydroxyl group of methanol can engage in hydrogen bonding with the benzene ring of toluene, reducing the polarity contrast between the two molecules and leading to miscibility.
In conclusion, despite the difference in polarity, toluene and methanol are miscible because methanol can form interactions with the non-polar toluene molecule through hydrogen bonding, making them blend in any ratio.