In chapters 5-7 of The Adventures of Huckleberry Finn, what poignancy is evoked in the conversation Huck overhears on the river?
I wonder if you are actually refering to what Huck overhears in Chapter Eight when he sees the boat full of his friends and loved ones who are eagerly looking for Huck or at least trying to find his body. This does not occur in Chapters 5-7 which do not contain any conversations that Huck overhears that could be considered poignant.
The reason why this event is poignant is that Huck's friends believe that he might have been killed, which is of course just what Huck wanted them to believe, as is indicated in the way that he created a scene to suggest this fact. Of course, Huck's friends don't know about this and are obviously upset and grief-stricken at the thought of Huck's death. Note how this scene is described:
By and by she come along, and she drifted in so close that they could a run out a plank and walked ashore. Most everybody was on the boat. Pap, and Judge Thatcher, and Bessie Thatcher, and Jo Harper, and Tom Sawyer, and his old Aunt Polly, and Sid and Mary, and plenty more. Everybody was talking about the murder, but the captain broke in and says:
"Look sharp, now; the current sets in the closest here, and maybe he's washed ashore and got tangled amongst the brush at the water's edge. I hope, so, anyway."
The way in which all of Huck's friends are talking about his supposed "murder" and Huck is so close adds both a poignant and slightly ironic note to the text, as they look for Huck's body on the river.