{"id":13328,"date":"2020-11-30T06:50:33","date_gmt":"2020-11-30T01:20:33","guid":{"rendered":"https:\/\/cbselibrary.com\/?p=13328"},"modified":"2020-11-30T15:26:21","modified_gmt":"2020-11-30T09:56:21","slug":"definition-acid-base","status":"publish","type":"post","link":"https:\/\/cbselibrary.com\/definition-acid-base\/","title":{"rendered":"What is the definition of an acid and a base?"},"content":{"rendered":"
What is the definition of an acid and a base?<\/strong><\/h2>\n
<\/p>\n
What are acids?<\/strong><\/p>\n
\n
The Swedish chemist, Arrhenius<\/strong> proposed the following definition of an acid. \nAn acid<\/strong> is a substance which ionises or dissociates in water to produce hydrogen ions, H+<\/sup><\/strong>.<\/li>\n
For example, hydrochloric acid, HCl(aq) is a solution of hydrogen chloride in water, obtained by dissolving pure hydrogen chloride gas in water. \nHCl(g) \u2192\u00a0HCl(aq) \nAs the gas dissolves in water, the hydrogen chloride molecule reacts with water and ionises to produce hydrogen ion, H+<\/sup>. \nHCl(aq) \u2192\u00a0H+<\/sup>(aq) + Cl–<\/sup>(aq) \nThe hydrogen ion then attaches itself to a water molecule to form the hydroxonium ion, H3<\/sub>O+<\/sup><\/strong>. \nH+<\/sup>(aq) + H2<\/sub>O(l) \u2192\u00a0H3<\/sub>O+<\/sup>(aq) \nHence, the overall equation for the ionisation of hydrogen chloride is given below. \nHCl(aq) + H2<\/sub>O(1) \u2192 H3<\/sub>O+<\/sup>(aq) + Cl–<\/sup>(aq) \n<\/li>\n
For the sake of convenience, the term \u2018hydrogen ion is used to replace \u2018hydroxonium ion and H+<\/sup>(aq) is used in place of H3<\/sub>O+<\/sup>(aq).<\/li>\n
Hence, the ionisation of hydrochloric acid in water can be represented as: \n<\/li>\n
Other acids ionise similarly in water. Examples: \n \n<\/li>\n
Hydrochloric acid is known as a monoprotic acid<\/strong>.\u00a0This acid contains only one ionisable hydrogen atom, producing only one hydrogen ion (proton) per molecule of acid.<\/li>\n
Polyprotic acids<\/strong> can produce more than one hydrogen ion per molecule of acid. Sulphuric acid is a diprotic acid<\/strong>, whereas phosphoric acid is a triprotic acid<\/strong>.<\/li>\n
Basicity<\/strong> of an acid is the number of ionisable hydrogen atoms per acid molecule.<\/li>\n
A number of non-metal oxides<\/strong> react with water to produce acidic solutions which contain hydrogen ions and turn blue litmus paper red. They are called acidic oxides<\/strong>. \n(a) Carbon dioxide reacts with water to form carbonic acid. \nCO2<\/sub>(g) + H2<\/sub>O(l) \u2192 H2<\/sub>CO3<\/sub>(aq) \n(b) Sulphur trioxide reacts with water to form sulphuric acid. \nSO3<\/sub>(g) + H2<\/sub>O(l) \u2192 H2<\/sub>SO4<\/sub>(aq) \n(c) Dinitrogen pentoxide reacts with water to form nitric acid. \nN2<\/sub>O5<\/sub>(g) + H2<\/sub>O(l) \u2192 2HNO3<\/sub>(aq)<\/li>\n
Not all non-metal oxides are acidic oxides. Only those that are able to react with water can produce acidic solutions. For example, carbon monoxide does not react with water. Therefore, carbon monoxide is classified as a neutral oxide<\/strong>.<\/li>\n
Acids are classified into two groups, mineral acids<\/strong> and organic acids<\/strong>.<\/li>\n
Mineral acids are obtained frdm minerals, whereas organic acids are extracted from animal and plant materials.<\/li>\n<\/ul>\n
Table 1 and Table 2 show some examples of mineral and organic acids.<\/strong><\/p>\n