Question

A. Draw the bonding pattern of water molecules with the amino acid glutamic acid at a pH of 7. Identify the hydrogen bond donors and hydrogen bond acceptors.

B. From a thermodynamic perspective, explain why table salt readily dissolves in water at room temperature.

Answer 1

(B)

From Gibb's free energy equation, delta G = delta H - T*delta S

A reaction is spontaneous if delta G<0. When a salt is disolved in water then we call it dissolution. Mostly all dissolutions of salts are endothermic means they need energy. It means delta H is little positive. in dissolution salts breaks into its ions, so the entropy also increases and it is positive. Temperature plays important role here. For most of the solids room temperature is good to dissolve them.

Water is a polar solvent and it has permanent dipole moment because of its bent geometry. It has negative charge on O atom and positive charge on H atoms. so, These oppositve charges attracts the oppositve ions of the salt. Like in NaCl, Na is positive and Cl is negative. So, when we put it in water then positive charge attracts the Cl- ions and negative charge attracts the Na+. Water molecules exerts a force on salt molecules and try to break them into ions.