Consider two brass vessels in which one is filled with water while another with curd. Do you know which one of the substance (water or curd) is useful for consumption and which is harmful and why. The water in brass vessel is healthy for consumption. But curd in brass vessel may cause food poisoning. Do you know the reason for that?
This is because the water stored in brass vessel causes dramatic fall in the level of E.coli which is present in drinking water due to presence of copper. On the contrary, curd is made from milk and contains lactic acid. Lactic acid reacts with copper and forms toxic compounds. It makes curd unfit for consumption and cause food poisoning. Thus, we should not keep curd and other acidic or sour food items in copper or brass vessels. It also reflects few properties of acidic substances that we can observe in our everyday life.
Similarly we are familiar with hyperacidity. The medical treatment to nullify the hyperacidity is the tablet or syrup of antacid. There is a substance that can nullify the effect of acids. This substance is called as base. The aqueous solution of base is called as alkali.
We can observe many acidic substances in our surroundings and can also identify their physical properties. For example; hydrochloric acid (HCl) is found in gastric juice and also causes hyperacidity; if found in excess.
Sulphuric acid is present in acid rain whereas nitric acid is mainly used in the manufacture of fertilisers and explosives. Carbonic acid in present in soft drink and Uric acid is present in urine.
Many acids like Malic acid, ascorbic acid, citric acid are found in fruits. The aqueous solution of acetic acid is well known as vinegar. Tannic acid is found in tea and wine. We can easily observe some common physical properties of acids such as corrosive nature, sour taste like lemons and vinegar. They release hydrogen ions in water therefore almost all acids are soluble in water. They are ionic in nature and good conductor of electricity. Acids turn blue litmus paper to a red colour. They forms salt with base and this reaction is called as neutralization reaction.
Similarly many household items contain basic substances such as toothpaste, soaps, bleach and many cleaning agents. Sodium hydroxide is major ingredient of soap. Calcium hydroxide, ammonium hydroxide and magnesium hydroxide are other most common bases. Like acids, bases are also corrosive in nature with soapy feel. They are bitter in taste and can turn red litmus paper to blue colour. They contain hydroxyl ions and also soluble in water. Due to presence of ions in basic solutions, they are good conductor of electricity.
Unlike physical properties, acids and bases show different chemical properties. Reaction with other substances also depends on the strength of acids and bases. The reaction of acid and base results the formation of salt and water.
Acids react with metal to release hydrogen gas. Reaction of hydrochloric acid with zinc gives salt (zinc chloride) with hydrogen gas.
2HCl + Zn ---> ZnCl2 + H2
Similarly sulphuric acid reacts with magnesium to form magnesium sulphate and releases hydrogen gas.
H2SO4 + Mg → MgSO4 + H2
On the contrary; very few metals react with bases such as aluminium metal reacts with NaOH and forms gelatinous precipitate of aluminium oxide.
Acids react with metallic hydrogen carbonates to form salts. For example; reaction of hydrochloric acid with sodium bicarbonate results the formation of sodium chloride (table salt) and carbonic acid which further dissociates to water and carbon dioxide.
NaHCO3 + HCl → NaCl + H2CO3
Strong and weak bases react with non-metallic oxides to form salts and water. This reaction proves that non-metallic oxides are acidic in nature such as barium hydroxide reacts with sulphur trioxide to form barium sulphate and water.
SO3(g) + Ba(OH)2(aq) → BaSO4(aq) + H2O(l)
Likewise reaction of sodium hydroxide with phosphorus pentoxide forms sodium phosphate and water.
P4O10(s) + 12 NaOH(aq) → 4 Na3PO4(aq) + 6 H2O(l)
We can observe many chemical properties of acid and base in our surroundings such as a tarnished copper vessel regains its shine after rubbing with lemon. This is because acid present in lemon reacts with copper oxide and expose untarnished copper metal.
Furthermore an old darkened copper penny can be made to shine in a solution of salt with vinegar. This is because table salt (NaCl) with acetic acid forms hydrochloric acid that can react with tarnished layer of copper oxide quickly. Acids react with metallic carbonates to form the respective salts, carbon dioxide and water.