Question

1. Are the solutions made from these compounds acidic, basic or neutral solutions? (10 pts total, 2 pts each) a. NaF b. RbC CSn(NO3) d. MgS e. Crla

Answer 1

Ans. #a. NaF: NaF is a salt of strong base (NaOH) and weak acid (HF). The cation of strong base (Na⁺) acts as the spectator ion, and has no effect on pH of solution.

The anion of weak acid acts as conjugate base and accepts protons from the medium as follow-

            F^- + H₂O <-------> HF + OH^-

So, the resultant solution is basic due to formation of OH^-.

#b. RbCl: It is a salt of strong acid (HCl) and strong base (group I hydroxide, RbOH). Both Cl^- (anion of string acid) and Rb⁺ (cation of strong base) act as spectator ion, and have no effect on the pH of the solution.

So, this solution is neutral.

#c. Sn(NO₃)₂ is a salt of weak base and strong acid (HNO₃).

The cation of weak base accepts OH^- from water molecules to make the solution acidic as follow-

            Sn²⁺ + 2 H₂O <---------> Sn(OH)₂ + 2 H⁺

#d. MgS: It’s a salt of strong base and weak acid (H₂S).

The anion of weak acid accepts proton from H₂O to make the solution basic as follow-

            S^2- + H₂O <-------> HS^- + OH^-

#e. CrI₃: It’s a salt of weak base Cr(OH)₃ and strong acid HI.

The cation of weak base accepts OH^- from water molecules to make the solution acidic as follow-

            Cr³⁺ + 3 H₂O <---------> Cr(OH)₃ + 3 H⁺