The cup shown above provides an example of tarnish, a chemical reaction caused when silver metal reacts with hydrogen sulfide gas produced by some industrial processes or as a result of decaying animal or plant materials: 2\text{Ag} + \text{H}_2\text{S} \rightarrow \text{Ag}_2\text{S} + \text{H}_2
The tarnish can be removed using a number of polishes, but the process also removes a small amount of silver along with the tarnish.

Single-Replacement Reactions
A single-replacement reaction is a reaction in which one element replaces a similar element in a compound. The general form of a single-replacement (also called single-displacement) reaction is:

A+BC \rightarrow AC+B
In this general reaction, element Ais a metal and replaces element B, also a metal, in the compound. When the element that is doing the replacing is a nonmetal, it must replace another nonmetal in a compound, and the general equation becomes:

Y+XZ \rightarrow XY+Z
Yis a nonmetal and replaces the nonmetal Zin the compound with X.

Metal Replacement
Magnesium is a more reactive metal than copper. When a strip of magnesium metal is placed in an aqueous solution of copper(II) nitrate, it replaces the copper. The products of the reaction are aqueous magnesium nitrate and solid copper metal.

\text{Mg}(s)+\text{Cu(NO}_3)_2(aq) \rightarrow \text{Mg(NO}_3)_2 (aq) + \text{Cu}(s)
This subcategory of single-replacement reactions is called a metal replacement reaction because it is a metal that is being replaced (copper).
QUESTION 1 DOK 1

Which of the following statements about single-replacement reactions is TRUE?

SELECT AN ANSWER

Copper will replace magnesium in a single-replacement reaction because it is less reactive.

The product of a single replacement reaction should always contain hydrogen gas.

Tarnish on silver is an example of a single replacement reaction: Ag replaces the H in hydrogen sulfide.

The formula for a non-metal replacing a non-metal is A + BC = AB + C.