Cocaine is a molecule made up of C, H, O and N atoms. It is a weak base¹ (the N has 3 bonds) and, in solution, it exists in 2 forms in an equilibrium: the free base² and the acid salt (see Figure 1). The predominant form in solution depends on the pH of the solution. In its free base form, the molecule is uncharged (unionized or non-polar³) and is not readily dissolved in an aqueous medium (water). When the free base is reacted with hydrochloric acid (low pH), the N accepts a H+ and forms the hydrochloride salt. In this form, cocaine is ionized⁴ and is water soluble. Because the hydrochloride salt dissolves in solution, it can be snorted⁵ or injected. However, the ionized form (salt) can not be smoked because it is so stable at high temperatures, it does not volatilize (vaporize) in the smoke (see Module 5). In contrast, the free base form of cocaine (unionized) is easily volatilized by high temperatures so that it can be breathed into the lungs. [By the way, this is true of other free bases including nicotine and morphine.] The free base is usually made by mixing the hydrochloride salt of cocaine with sodium bicarbonate (baking soda). When the liquid mixture is evaporated, the solid “lump” of cocaine can be crushed up and heated (“crack⁶“). Free base heroin or amphetamine (“ice”) are made the same way.

Definitions:
¹ A compound that tends to accept a H+ when placed in an acidic solution.
² The unionized form of a weak base. With reference to cocaine, it is the smokable form.
³ A chemical property of a substance that indicates an even distribution of charge within the molecule. A non-polar or non-charged compound mixes well with organic solvents and lipids but not with water.
⁴ An atom, radical, or molecule that has gained or lost one or more electrons. Therefore it acquires a net negative or positive charge.
⁵ To breathe in a compound in a solid form through the nostrils. With reference to cocaine, it is the hydrochloride salt.
⁶ The short term for a smokable form of cocaine (the free base).

Figures:

Figure 1: Treating the cocaine free base with HCl generates the charged form of cocaine, or the ‘acid salt’. Conversely, treating the acid salt with a base such as sodium bicarbonate (baking soda) yields the free base form of cocaine.