HAZMAT Technician Practice Exam

What characterizes unsaturated hydrocarbons?

1. They contain only single bonds

2. They have at least one multiple bond between carbon atoms

3. They are less reactive than saturated hydrocarbons

4. They only exist as gases at room temperature

The correct answer is: They have at least one multiple bond between carbon atoms

Unsaturated hydrocarbons are characterized by the presence of at least one multiple bond—either a double or triple bond—between carbon atoms. This structural feature results from the inability of carbon to form four single bonds due to the presence of these additional bonds, leading to fewer hydrogen atoms being attached to the carbon skeleton compared to saturated hydrocarbons, which contain only single bonds and are fully saturated with hydrogen. This characteristic makes unsaturated hydrocarbons generally more reactive than their saturated counterparts. The double or triple bonds are sites of reactivity that can participate in various chemical reactions, such as addition reactions. This enhanced reactivity is a key distinction between unsaturated and saturated hydrocarbons. In contrast, saturated hydrocarbons, which contain only single bonds and a maximum number of hydrogen atoms per carbon, are typically less reactive. While unsaturated hydrocarbons can be gases, liquids, or solids at room temperature, the assertion that they only exist as gases is inaccurate, as many unsaturated compounds can also be found in liquid form. Therefore, the defining feature of unsaturated hydrocarbons is their multiple bonds, which fundamentally influence their chemical behavior.