Which of the following compounds of silver is soluble in water ?

Options

A. AgF
B. AgCI
C. AgBr
D. AgI

Answer

A

Explanation

The most important and most stable oxidation state of silver is `+1`. In almost all the simple compounds of silver, the metal has a `+1` oxidation state, and the `Ag^(+)` ion is the only water-stable ion of he element. Hence it is common to substitue ''silver'' for ''silver (I)''. All the halides of silver `(+1)` are known. Practically all Ag `(+1)` salts are insoluble in water. Exceptions include Ag `NO_(3)`, AgF and `AgCIO_(4)` which are soluble. The abnortmal insolubilities of Ag X other than AgF are due to their abonormally high lattice enthalpies. The reason for usuaually high lattice enthalpies lies in the strong van der Waals attraction between `Ag^(+)` and `X^(-)` ions in addition to the usual electrostaic attraction between the oppositely charged ions. Let's compare AgCI with KCI, both `Ag^(+)` (126 pm) and `K^(+)` (133 pm) ions have similar radii, but `Ag^(+)` has 46 electrons while `K^(+)` ion has only 18 electrons. In general, the larger the number of electron in an ion, the stronger is its van der Waals attraction for neighbouring ions. Consequently, the lattice enthalpy of Ag (214 Cal/mole) is relatively higher that than of KCI (168 KCal `"mole"^(-1)`). Hence, AgCI is much less soluble in water than KCI. The lattric enthalpies of AgBr and Agl are even higher because of greater number of electrons in their anions. Consequently, they are les soluble than AgCI. The lattice enthalpy of AgF is the lowest because of the least number of electon in its anion. Thus, AgF is water soluble. AgF may be prepared by the action of HF acid on `Ag_(2)O`. The white AgCI and yellow Ag Br and AgI are most conveniently made by double decomposition:
`Ag^(+) (aq) + X^(-) (aq) rarr Ag X (s)`