Question

A solid piece of silver metal reacts with oxygen in the air and tarnishes. What type of reaction is it?
A.Decomposition
B.Synthesis
C.Combustion
D.Single replacement

Answer 1

Hint: The word tarnishing means to make or become less bright or a different colour. It usually occurs in metals like copper, brass, aluminium, magnesium, neodymium and other similar metals

Complete step by step answer:
Tarnish is a type of chemical reaction formed as a product when a metal and a nonmetal compound, especially oxygen and sulfur dioxide react and undergo oxidation. The reaction for tarnishing can be represented as:
\[\begin{gathered}
  8Ag + 4H{S^ - } \to {\text{ }}4A{g_2}S{\text{ }} + {\text{ }}2{H_2}\; + {\text{ }}4{e^ - } \\ {O_2}\; + {\text{ }}2{H_2}O{\text{ }} + {\text{ }}4{e^ - }\; \to {\text{ }}4O{H^ - } \\
\end{gathered} \]
Now let us analyze each of the options systematically:
A decomposition reaction is a chemical reaction in which one reactant breaks down into two or more products. \[AB \to A{\text{ }} + {\text{ B}}\]. Where AB is the parent molecule (reactant) and A & B are the product molecules.
A synthesis reaction is a chemical reaction in which two different atoms or molecules interact to form a different molecule or compound.Generally, a synthesis reaction is exothermic as energy is released.
Combustion is a type of reaction in which a molecule reacts in presence of oxygen liberating heat. The reactant molecule is known as the fuel and the source of oxygen is called the oxidizer.
Single replacement reaction, there is a substitution of one element with another element in a compound. The starting materials for this reaction always consist of pure elements, like pure zinc metal or hydrogen gas, plus an aqueous compound.
From the reaction, we can see that there is an interaction of molecules resulting in a new compound.

Therefore, we can conclude that the correct answer to this question is option B.

Note:
The prevention of tarnish can be achieved by the use of barriers such as lacquers to prevent the reactive chemical species contacting the silver. Silver objects are routinely coated with a cellulose nitrate-based lacquer after cleaning. In the coating there is addition of corrosion inhibitors.