Transition and InnerTransition Elements - Result Question 144
####44. Which of the following halides react(s) with $AgNO _3(a q)$ to give a precipitate that dissolves in $Na _2 S _2 O _3(a q)$ ?
(a) $HCl$
(b) $HF$
(c) $HBr$
(d) $HI$
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Answer:
Correct Answer: 44. $(a, c, d)$
Solution:
- Solubilities of silver halides in water decreases from fluoride $(AgF)$ to iodide $(AgI)$. Silver fluoride is readialy soluble in water, hence when $AgNO _3$ solution is added to HF solution (HF being weak acid, its solution maintain very low concentration of $F^{-}$) no precipitate of $AgF$ is formed.
$HCl, HBr$ and $HI$ being all strong acid, forms precipitates of $AgCl, AgBr$ and $AgI$ when $AgNO _3$ solution is added to their aqueous solution.
The solubilities decreases from $AgCl$ to $AgI, AgCl$ dissolves in aqueous ammonia, $AgBr$ dissolves only slightly in concentrated ammonia while $AgI$ does not dissolve in ammonia solution.
$Na _2 S _2 O _3$ solution dissolve all three, $AgCl, AgBr, AgI$ by forming complex $\left[Ag\left(S _2 O _3\right) _2\right]^{3-}$ as $S _2 O _3^{2-}$ is a stronger complexing agent than ammonia.
