Question

a) Predict in which direction the following reactions will proceed. Justify your answers briefly.

I. HCl + NaF ---- HF + NaCl

II. AlBr3 + 3 NaF ---- AlF3 + 3 NaBr

III. Ti(OMe)4 + 2 TiBr2 ---- TiBr4 + 2 Ti(OMe)2

IV. SrS + HgO ---- SrO + HgS

V. [Pt(CN)4]2- + 4 NaCl ---- [PtCl4]2- + 4 NaCN

VI. CoCl2 + CdI2 ---- CoI2 + CdCl2

VII. [Ag(NH3)2]NO3 + 2 NaSCN ---- NaNO3 + Na[Ag(SCN)2]

+ 2 NH3

b) Dimethylmercury, Hg(CH3)2, is one of the strongest known neurotoxins. Is it safe to mix mercuric fluoride, HgF2, with methyl lithium, LiCH3? Explain your decision.

c) Dimethylmagnesium, Mg(CH3)2, reacts violently with water, while Hg(CH3)2 is remarkably stable in aqueous environment. Explain this observation and provide a chemical equation for the reaction involving Mg(CH3)2.

Answer 1

I). HCl + NaF ---- HF + NaCl

It will proceed in forward direction, because HCl is stronger acid than HF.

II. AlBr3 + 3 NaF ---- AlF3 + 3 NaBr

It will proceed in forward direction, because F- is hard base and it can form strong bond with hard acid according to Pearson Hard-Soft acid base theory (Hard acids prefer to bind with hard bases and soft acids prefer to bind with soft bases). Between Na+ and Al3+, Al3+ is hard acid. So AlF3 is more stable than NaF.

III. Ti(OMe)4 + 2 TiBr2 ---- TiBr4 + 2 Ti(OMe)2

MeO- is hard base and Ti4+ is hard acid. So this reaction proceed in backward direction as Ti(OMe)4 is more stable.

IV. SrS + HgO ---- SrO + HgS

HgS is more stable as Hg2+ is soft acid and S2- is soft base. So this reaction proceeds in forward direction.

V. [Pt(CN)4]2- + 4 NaCl ---- [PtCl4]2- + 4 NaCN

    Pt2+ is soft acid so it can form strong complex with soft base like CN-. This reaction proceeds in backward direction.

VI. CoCl2 + CdI2 ---- CoI2 + CdCl2

   Cd2+ is larger ion so it is soft acid. I- is softer base than Cl-. so CdI2 is more stable hence this reaction proceeds in backward direction.

VII. [Ag(NH3)2]NO3 + 2 NaSCN ---- NaNO3 + Na[Ag(SCN)2]+ 2 NH3

    SCN- is soft base and Ag+ is soft acid so This reaction proceeds in forward direction.