A Level Chemistry OCR Practice Exam

In an addition reaction, what is typically formed by the addition of a reactant?

1. A saturated molecule

2. An unsaturated molecule

3. A polymer

4. A gaseous product

The correct answer is: A saturated molecule

In an addition reaction, the characteristic outcome is the formation of a saturated molecule. An addition reaction involves the addition of reagents across a double or triple bond present in an unsaturated compound, such as alkenes or alkynes. When these unsaturated compounds react, the multiple bonds break, allowing new atoms or groups to be added to the molecule. The result of this process is a saturation of the carbon bonds, which means that each carbon atom becomes involved in single bonds with other atoms, thus eliminating the double or triple bonds that characterized the original molecule. This transformation leads to the formation of saturated hydrocarbons, which can contribute to a variety of products such as alkanes, depending on the specific reactants involved in the reaction. In contrast, an unsaturated molecule would indicate that there are still double or triple bonds present, and therefore cannot be the product of an addition reaction. Similarly, while addition reactions can contribute to the formation of polymers or generate gaseous products under certain conditions, those are not defining characteristics of all addition reactions. The primary feature to highlight is the conversion of unsaturated molecules into saturated ones as a direct result of the reaction.