An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid.
Acidic substances are usually identified by their sour taste. An acid is basically a molecule which can donate an H+ ion and can remain energetically favourable after a loss of H+. Acids are known to turn blue litmus red.
Bases, on the other hand, are characterized by a bitter taste and a slippery texture. A base that can be dissolved in water is referred to as an alkali. When these substances chemically react with acids, they yield salts. Bases are known to turn red litmus blue.
Acid Definition Chemistry
The terms acid and base have been defined in different ways, depending on the particular way of looking at the properties of acidity and basicity. Arrhenius first defined acids as compounds which ionize to produce hydrogen ions, and bases as compounds which ionize to produce hydroxide ions. According to the Lowry-Bronsted definition, an acid is a proton donor and a base is a proton acceptor.
According to the Lewis definition, acids are molecules or ions capable of coordinating with unshared electron pairs, and bases are molecules or ions having unshared electron pairs available for sharing with acids. To be acidic in the Lewis sense, a molecule must be electron deficient. This is the most general acid base concept. All Lowery Bronstead acids are Lewis acids but, in addition, the Lewis definition includes many other reagents such as boron trifluoride, aluminium chloride, etc.
Theories of Acids and Bases
Three different theories have been put forth in order to define acids and bases. These theories include the Arrhenius theory, the Bronsted-Lowry theory, and the Lewis theory of acids and bases. A brief description of each of these theories is provided in this subsection. Acids and bases can be defined via three different theories.
The Arrhenius theory of acids and bases states that "an acid generates H+ ions in a solution whereas a base produces an OH– ion in its solution".The Bronsted-Lowry theory defines "an acid as a proton donor and a base as a proton acceptor".Finally, the Lewis definition of acids and bases describes "acids as electron-pair acceptors and bases as electron-pair donors".pH of Acids and Bases
In order to find the numeric value of the level of acidity or basicity of a substance, the pH scale (wherein pH stands for 'potential of hydrogen') can be used. The pH scale is the most common and trusted way to measure how acidic or basic a substance is. A pH scale measure can vary from 0 to 14, where 0 is the most acidic and 14 is the most basic a substance can be.
Another way to check if a substance is acidic or basic is to use litmus paper. There are two types of litmus paper available that can be used to identify acids and bases – red litmus paper and blue litmus paper. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions.
1.Properties of AcidsAcids are corrosive in nature.They are good conductors of electricity.Their pH values are always less than 7.When reacted with metals, these substances produce hydrogen gas.Acids are sour in taste.2. Properties of Bases
Some properties, like a bitter taste, are owned by all bases. The bases feel slippery, too. Dream on what slippery soap looks like. And this is a foundation. Furthermore, when immersed in water, bases conduct electricity because they consist of charged particles in the solution.
They are found to have a soapy texture when touched.These substances release hydroxide ions (OH– ions) when dissolved in water.In their aqueous solutions, bases act as good conductors of electricity.The pH values corresponding to bases are always greater than 7.Bases are bitter-tasting substances which have the ability to turn red litmus paper blue.
3. Neutral Substances
The neutral substance is a substance which is not acidic or basic, has the same amount of hydrogen and hydroxyl ions, and does not alter the colour of the litmus surface.
These substances do not display any acidic or basic characteristics.Their pH values approximate to 7.Neutral substances have no effect on red or blue litmus paper.The pH of pure water is exactly 7.Examples: Water, Common salt (NaCl)AcidsBasesAcid gives off hydrogen ions when dissolved in water.Bases give off hydroxyl ion when dissolved in water.It turns blue colour litmus paper into red.It turns red colour litmus paper into blue.It has a sour taste.It has bitter taste and soapy to touch.Its pH value ranges from 1 to 7.Its pH value ranges from 7 to 14.Example: HCl, H2SO4 etc.Example: NaOH, KOH etc.Arrhenius Concept of Acids and BasesThe Swedish scientist Svante August Arrhenius defined acids as substances that increase the H+ ion concentration of water when dissolved in it.These protons go on to form hydronium ions (H3O+) by combining with water molecules.Similarly, the Arrhenius definition of a base states that bases are the substances that, when dissolved in water, increase the concentration of OH– ions in it.One of the merits of this theory is that it successfully explains the reaction between acids and bases that yield salts and water.An important limitation of the Arrhenius definitions of acids and bases is that it fails to explain how substances lacking hydroxide ions form basic solutions when dissolved in water, such as NO2– and F–.Bronsted Lowry Theory of Acids and BasesThe Bronsted-Lowry theory defines an acid as a donor of protons.A base is defined as a proton acceptor (or H+ ion acceptor) by this theory.Bronsted acids undergo dissociation to yield protons and therefore increase the concentration of H+ ions in the solution.On the other hand, Bronsted bases accept protons from water (the solvent) to yield hydroxide ions.An advantage of the Bronsted-Lowry definition of acids and bases is its ability to explain the acidic or basic nature of ionic species.An important limitation of this theory is that it fails to explain how compounds lacking hydrogen exhibit acidic properties, such as BF3 and AlCl3.
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