Answer to Question #269426 in General Chemistry for Deep

Question

What does it mean if, during a single replacement reaction, a black substance has formed on top of the Magnesium strip? How would this be described in a lab procedure?

Answer 1

This can happen in a reaction between Lead Nitrate and Magnesium

The Magnesium displaces the Lead from solution to form Magnesium Nitrate.This is because Magnesium is more reactive than Lead.

Magnesium turn black as it becomes coated in a layer of lead that has been displaced from the Lead Nitrate solution.

$Pb (NO_3)2+Mg\to\>Mg(NO_3)2+Pb$

This is called a metal replacement reaction.

A coating of Lead is observed if Magnesium is thick enough.