Reaction of hydrogen halide with silver nitrate

Question: which of the following hydrogen halide reacts with silver nitrate (aq.) to give a precipitate that dissolves in Na₂S₂O₃ (aq.)?

a)      HCl

b)      HF

c)       HBr

d)      H I

Solution: When silver nitrate (AgNO_3(aq)) reacts with hydrogen halde (HX), a double replacement reaction takes place:

A double replacement reaction is a chemical reaction where two reactant ionic compounds exchange ions to form two new product compounds with the same ions.

where X = Cl, Br, or I.

The silver of silver nitrate reacts quickly with hydrogen halide to produce silver halides which are insoluble so they form a precipitate. Except F all other halides (Cl, Br, I) give precipitate with Ag.

AgF is soluble; no precipitate formed

AgCl forms a white precipitate

AgBr forms a cream precipitate

AgI forms a yellow precipitate

This precipitate dissolves on reaction with Na₂S₂O₃ (aq.)

Thus options a, c, d are correct and give precipitate with silver nitrate which dissolve in Na₂S₂O₃ (aq.).