What ions do alkalis release in solution?

Alkalis release hydroxide ions (OH-) when dissolved in solution.

Alkalis are substances that can accept hydrogen ions (H+) and are typically found on the right-hand side of the periodic table. When alkalis dissolve in water, they dissociate or break apart into their constituent ions. This process is known as ionisation. The key ion that alkalis produce in solution is the hydroxide ion (OH-).

For example, when sodium hydroxide (NaOH), a common alkali, dissolves in water, it ionises into sodium ions (Na+) and hydroxide ions (OH-). The equation for this process is: NaOH (s) → Na+ (aq) + OH- (aq). The (s) denotes a solid, while (aq) denotes an aqueous or water-based solution.

The presence of hydroxide ions is what gives alkalis their basic properties. These ions are capable of reacting with hydrogen ions (H+) to form water (H2O). This neutralisation reaction is the basis for many applications of alkalis, such as in antacids to neutralise stomach acid, or in soaps and detergents to break down fats and oils.

It's important to note that the strength of an alkali (its alkalinity) is determined by the concentration of hydroxide ions it produces in solution. The more hydroxide ions an alkali produces, the stronger it is. This is measured on the pH scale, where a higher pH indicates a stronger alkali.

In summary, alkalis release hydroxide ions when they dissolve in water, and it's these ions that give alkalis their characteristic properties. Understanding this process is fundamental to understanding the behaviour of alkalis and their role in chemical reactions.