 In this video, we are going to learn about what makes things alkaline or basic. Alkaline materials are usually used to make cleaning products, like soap, and ceramics, such as tiles. They neutralize acids and so can be used to ease indigestion and remove harmful gases from industrial chimneys that contribute to acid rain. To test for an alkali, expose it to red litmus paper, and alkali should turn the paper blue. An alkali is considered an ionic compound made using the positively charged cations of alkali or alkali earth metals from groups 1 and 2 of the periodic table. A broader definition is any base that dissolves in water, and in this case ammonia is also an alkali. All alkalis are bases, but not all bases are alkalis. A base forms a slippery aqueous solution, tastes bitter, has a pH above 7, and reacts with acids to form salts. There are many definitions for bases. In Arrhenius theory, a base dissociates in water to form hydroxide ions. The Arrhenius definition is a very narrow definition, in which only hydroxides are basic. We can see that bases react with acids to produce water and salt. In Lewis theory, a base is an electron pair donor. The Lewis definition is a very broad definition, in which a wide range of chemical behaviour may be described as basic behaviour. In Bronsted-Lowry theory, a base is a proton or H plus ion acceptor. Let's stick with this definition. Notice that all of these equations are equilibria. Kb is the equilibrium constant for the base reaction, and describes the extent of H plus uptake by the base, b. Kb is equal to the concentration of Hb plus over the concentration of b, times the concentration of H plus. The higher Kb, the greater the extent of H plus uptake, so the stronger the base. Kb is associated with the pH scale. We use pH to tell us how strong acids and bases are, usually on a scale of 1 to 14, where 7 is neutral, like water. There are many kinds of indicator for pH scale. Funalphaline is a good indicator for alkalis. It turns from clear to pink at around pH 10, whereas methyl orange is not so good. It undergoes its colour changes below pH 7. Mostly, universal indicator is used because it has a full spectrum of colours for pH indicating. Strong alkalis include hydroxides, carbannions, amides, and hydrides of group 1 metals. Sodium hydride is known as a superbase. Strong bases are very dangerous. Why do you think this is? Strong bases are very reactive, and thus they are corrosive. Many cleaning fluids are strong bases. Organic alkalis are usually weaker. Very weak alkalis include chemicals like ammonia, which use their lone pair of electrons to accept protons. They do not dissociate in water to give a negatively charged ion, so the bond to H+, is weaker.