Category : 7th Class
Acids, Bases and Salts
Acids
Acids are found in small amounts in nature. For example, acids are present in things that we eat such as lemon and orange contains citric acid, tomato contains oxalic acid, vinegar contains acetic acid, yoghurt contains lactic acid and frizzy drinks contain carbonic acid. Acids found in foods are mild. Acids such as hydrochloric acid \[(HCL),\] sulphuric acid\[({{H}_{2}}S{{O}_{4}})\] and nitric acid \[(HN{{O}_{3}})\] are called mineral acids. They are strong acids. Touching strong acids can cause acid burns.
Acids are formed by dissolving oxides of non-metals such as carbon, sulphur and nitrogen in water. The oxides of non-metals are acidic because when dissolved in water they form acids For example:
\[C{{O}_{2}}+{{H}_{2}}O\to {{H}_{2}}C{{O}_{3}}\]
\[S{{O}_{3}}+{{H}_{2}}O\to {{H}_{2}}S{{O}_{4}}\]
\[3N{{O}_{2}}+{{H}_{2}}O\to NO+2HN{{O}_{3}}\]
Behaviour of Acidic Substances
The acidic substances show the following behaviour:
\[Fe+{{H}_{2}}S{{O}_{4}}\to FeS{{O}_{4}}+{{H}_{2}}\]
\[N{{a}_{2}}C{{O}_{3}}+2HCl\to 2NaCl+{{H}_{2}}O+C{{O}_{2}}\]
Bases
Bases are generally the oxides and hydroxides of metals. For example, sodium oxide \[(N{{a}_{2}}O),\] calcium oxide \[(CaO),\] sodium hydroxide \[(NaOH),\] etc. Soaps, toothpastes, solution of washing soda, soap solution, slaked lime and whitewash are some examples of basic substances.
The bases that are soluble in water are called alkalis. For example, sodium hydroxide \[(NaOH),\] potassium hydroxide \[(KOH),\] calcium hydroxide \[(Ca{{(OH)}_{2}})\] and ammonium hydroxide \[(N{{H}_{4}}OH).\] Sodium hydroxide and potassium hydroxide are called caustic alkalis because they burn the skin.
Formation of Bases
Bases can be formed in the following ways:
\[2Mg+{{O}_{2}}\,\,\,\,\to \,\,\,2MgO\]
\[2Na+2{{H}_{2}}O\,\,\,\to \,\,\,\,2NaOH+{{H}_{2}}\]
Behaviour of Basic Substances
The basic substances show the following behaviour:
Salts
Salts are neutral substances found in abundance in the earth's crust. Salts are also dissolved in water and found in lakes, rivers and sea. Sea water contains salts such as chlorides, bromides, iodides and sulphates of sodium, potassium, magnesium and calcium.
Salts are also present in fruits and vegetables.
Salts are formed in the following ways:
\[2Na+C{{l}_{2\,\,}}\,\,\to \,\,\,\,\,2NaCl\,\,\]
\[Mg+2HCl\to MgC{{l}_{2}}+{{H}_{2}}\]
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