Difference Between Alkali and Acid

Alkali vs Acid
 

The word alkali is often used interchangeably to address highly basic solutions and alkali metals. In this context, alkali is referred to the alkali metals.

Alkali

Alkali term is commonly used for the metals in the group 1 of the periodic table. These are also known as alkali metals. Although H is also included in this group, it is somewhat different. Therefore, lithium (Li), sodium (Na), potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr) are members of this group. Alkali metals are soft, shiny, silvery color metals. They all have only one electron in their outer shell, and they like to remove this and form +1 cations. When the outer most electrons are excited, it comes back to the ground state while emitting radiation in the visible range. The emission of this electron is easy, thus alkali metals are very reactive. The reactivity increases down the column. They form ionic compounds with other electronegative atoms. More accurately, alkali is referred to the carbonate or the hydroxide of an alkali metal. They also have basic properties. They are bitter in taste, slippery, and react with acids to make them neutralized.

Acid

Acids are defined in several ways by various scientists. Arrhenius defines an acid as a substance that donates H3O⁺ ions in the solution. Bronsted- Lowry defines a base as a substance that can accept a proton. Lewis acid definition is far common than the above two. According to it, any electron pair donator is a base. According to the Arrhenius or Bronsted-Lowry definition, a compound should have a hydrogen and the ability to donate it as a proton to be an acid. But according to Lewis, there can be molecules, which don’t possess hydrogen, but can act as an acid. For example, BCl₃ is a Lewis acid, because it can accept an electron pair. An alcohol can be a Bronsted-Lowry acid, because it can donate a proton; however, according to Lewis, it will be a base.

Regardless of the above definitions, we normally identify an acid as a proton donor. Acids have a sour taste. Lime juice, vinegar are two acids we come across at our homes. They react with bases producing water, and they react with metals to form H₂,; thus, increase metal corrosion rate. Acids can be categorized into two, based on their ability to dissociate and produce protons. Strong acids like HCl, HNO₃ are completely ionized in a solution to give protons. Weak acids like CH₃COOH are partially dissociates and give fewer amounts of protons. K_a is the acid dissociation constant. It gives an indication of the ability to lose a proton of a weak acid. To check whether a substance is an acid or not we can use several indicators like litmus paper or pH paper. In the pH scale, from 1-6 acids are represented. An acid with pH 1 is said to be very strong, and as the pH value increases, acidity is decreased. Moreover, acids turn blue litmus to red.