single replacement reaction help

[Previous Community Member]

I am having my students complete a general single replacement reaction with CuSo,(aq) and Fe(s) (in the form of steel wool.) The copper comes out of solution and seems to adhere to the steel wool. The solution itself turns light green showing that the Fe replaced the Cu in the solution. However, The solid Cu appears to bind to the steel wool threads rather than replace them. Does the Cu take on the shape of the steel wool threads or is there some coating going on?

[mpheaney]

It's not exactly a coating nor is it taking on the shape of the threads, it appears to adhere to the steel wool, because that is where the reaction is taking place, so it's gonna stay in that location until something pushes it off, simply stirring or adding some sort of motion to the water will cause the copper to start coming off. So yes it has some adherence to the steel wool, but only because there are very weak attractive forces likely holding them together. I have a time lapse of some silver precipitating on copper from a solution of silver nitrate, in the video all I did was simply use a wash bottle to push off the silver that had accumulated, and it immediately sank to the bottom since nothing was keeping it suspended other than some very weak attractive forces and friction. However I am having trouble with uploading the video so we will have to do without it sadly.

[hansonja]

You would probably have to take a thread out and cross-section it to know for sure.  But the reaction will occur at the surface of the steel wool, and once there is a coating of copper the solution no longer has access to the steel.