An Experimental Study of The Ionicity of Hgclbr

Introduction

It has been experimentally established that in a solid-solid capillary reaction between two reactants, at least one of which is fairly ionic having a small inorganic impurity mixed with these, the amount of the product formed, at a given time, is more for an impurity the molecule of which has a higher electric dipole moment compared to the case of an impurity the electric dipole moment of which is less.  This amount of the impurity is taken such that, in each case, there are nearly same number of impurity molecules.

This is seen to be the case from Fig. 1 which presents a plot of (log₁₀x) x10² vs. (log₁₀t ) x 10², where x is the thickness of the product at time t after the start of the experiment for the system CuI-HgCl₂.

Figure 1: Kinetics of solid-solid reactions between Cul+HgCl2 with different inorganic solid impurities at 80oC Click here to View figure

 

The numerical data are given in Table 1.   We see that the amount of the product, for a given time, depends monotonically on the electric moment of the impurity molecule.  The electric dipole moment have been taken from ref. 1.  This is in accordance with a plausible theory.

Table 1: Thickness of product layer with pure reactants and different Impurities (In increasing dipole moment order)

Time	Thickness of product layer (log10 x i )×102
(log10t i)	Pure	HgClBr	HgClBr	HgClBr	HgBrI	NaCl	NaI	KCl
×102	Reactants	Ist method	IInd method	IIIrd method
– 60.2 – 30.1 -12.5 0.0 9.70 17.6 24.3 30.1 35.2 39.8 43.9 47.7	-215 -205 -196 -189 -180 -174 -170 -170 -170 -170 -170 -170	-205 -200 -200 -200 -200 -200 -200 -200 -200 -200 -200 -200	-210 -200 -200 -196 -196 -196 -196 -196 -196 -196 -196     -196	-210 -200 -200 -200 -196 -196 -196 -196 -196 -196 -196 -196	-210 -200 -196 -192 -192 -189 -189 -189 -189 -189 -189 -189	-185 -180 -174 -172 -170 -168 -166 -164 -164 -164 -160 -160	-182 -177 -172 -170 -168 -166 164 -162 -160 -160 160 -160	-180 -174 -170 -166 -162 -159 -157 -155 -155 -155 -155 -155

The curve for HgClBr, as prepared by three different methods and a curve for HgBrI are also shown in the figure.  All these curves occur at the bottom of the figure well below the curve for the pure reactants.  This goes to show that HgClBr as well as HgBrI have low ionicity.  This is in accord with Pauling’s simple semi-empirical theory of ionicity². Details may be presented elsewhere.

This was presented in Poster form at the International Conference held at IIT, Roorkee.

Acknowledgements

1. Lide D.R., CRC handbook of Chemistry and Physics, CRC Press, 2002.
2. Pauling L., The nature of the chemical bond, 3^rd edition, Oxford & IBH Publishing Co, p.98.

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