`color{green}(★)` Sour and bitter tastes of food are due to acids and bases, respectively, present in them.
`color{green}(★)` Acids are sour in taste and change the colour of blue litmus to red.
`color{green}(★)` Bases are bitter and change the colour of the red litmus to blue.
`color{green}(★)` Litmus is a natural indicator, turmeric is another such indicator.
`color{green}(★)` Synthetic indicators such as methyl orange and phenolphthalein to test for acids and bases.

`color{red}("𝐉𝐔𝐒𝐓 𝐅𝐎𝐑 𝐂𝐔𝐑𝐈𝐎𝐔𝐒")`

`color{green}(★)` A stain of curry on a white cloth becomes reddish-brown when soap, which is basic in nature, is scrubbed on it and it turns yellow again when the cloth is washed with plenty of water.

`color{green}(★)` Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator. When the litmus solution is neither acidic nor basic, its colour is purple. There are many other natural materials like red cabbage leaves, turmeric, coloured petals of some flowers such as Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a solution. These are called acid-base indicators or sometimes simply indicators.

`color{green}("𝐎𝐋𝐅𝐀𝐂𝐓𝐎𝐑𝐘 𝐈𝐍𝐃𝐈𝐂𝐀𝐓𝐎𝐑𝐒:")` Substances whose odour changes in acidic or basic media. These are called olfactory indicators.For eg: vanilla, onion and clove.


`color{red}("𝐑𝐄𝐀𝐂𝐓𝐈𝐎𝐍 𝐎𝐅 𝐀𝐂𝐈𝐃𝐒 𝐀𝐍𝐃 𝐁𝐀𝐒𝐄𝐒 𝐖𝐈𝐓𝐇 𝐌𝐄𝐓𝐀𝐋𝐒:")`



`color{green}("𝐑𝐄𝐀𝐂𝐓𝐈𝐎𝐍 𝐎𝐅 𝐀𝐂𝐈𝐃𝐒 𝐖𝐈𝐓𝐇 𝐌𝐄𝐓𝐀𝐋𝐒")`


`color{green}("𝐎𝐁𝐒𝐄𝐑𝐕𝐀𝐓𝐈𝐎𝐍 :")` Metal in the above reactions displaces hydrogen from the acids. This is seen as hydrogen gas. The metal combines with the remaining part of the acid and forms a compound called a salt. Thus, the reaction of a metal with an acid can be summarised as –


`color{red}("𝐀𝐜𝐢𝐝 + 𝐌𝐞𝐭𝐚𝐥 → 𝐒𝐚𝐥𝐭 + 𝐇𝐲𝐝𝐫𝐨𝐠𝐞𝐧 𝐠𝐚𝐬")`

• 𝐄𝐱𝐚𝐦𝐩𝐥𝐞 : Zinc granules react with dilute Hydrochloric acid in a test tube

`color{red}(2HCl + Zn → ZnCl_2 + H_2)`


• 𝐄𝐱𝐚𝐦𝐩𝐥𝐞 : Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.

`color{red}(Zn + 2HCl → ZnCl_2 + H_2)`

Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal.

`color{red}(2Na + 2HCl → 2NaCl + H_2)`

Hydrogen gas and iron chloride are formed when hydrochloric acid reacts with iron.

`color{red}(Fe + 2HCl → FeCl_2 + H_2)`

Hydrogen gas and zinc sulphate are formed when zinc metal reacts with sulphuric acid .

`color{red}(Zn + H_2SO_4 → ZnSO_4 + H_2)`

`color{green}("𝐑𝐄𝐀𝐂𝐓𝐈𝐎𝐍 𝐎𝐅 𝐁𝐀𝐒𝐄 𝐖𝐈𝐓𝐇 𝐌𝐄𝐓𝐀𝐋𝐒 :")`



`color{green}("𝐎𝐁𝐒𝐄𝐑𝐕𝐀𝐓𝐈𝐎𝐍:")` The reaction that takes place can be written as follows. Hydrogen is formed in the reaction.

`color{red}(2NaOH + Zn → underset("(Sodium zincate)")(Na_2ZnO_2) + H_2)`

`color{green}("𝐎𝐁𝐒𝐄𝐑𝐕𝐀𝐓𝐈𝐎𝐍:")` The reactions occurring in the above Activity are written as –


`color{red}("𝐓𝐞𝐬𝐭 𝐭𝐮𝐛𝐞 𝐀 : " Na_2CO_3(s) + 2HCl (aq) → 2NaCl (aq) + H_2O(l) + CO_2(g))`

`color{red}("𝐓𝐞𝐬𝐭 𝐭𝐮𝐛𝐞 𝐁 : " NaHCO_3(s) + HCl(aq) → NaCl (aq) + H_2O(l) + CO_2(g))`

On passing the carbon dioxide gas evolved through lime water,

`color{red}(underset("(Lime water)") (Ca(OH)_2 (aq)) + CO_2(g) → underset("(White precipitate)")(CaCO_3(s)) + H_2O(l))`

On passing excess carbon dioxide the following reaction takes place :

`color{red}(CaCO_3 (s) + H_2O(l) + CO_2(g) → underset("(Soluble in water)")(Ca(HCO_3)_2 (aq)))`

Limestone, chalk and marble are different forms of calcium carbonate. All metal carbonates and hydrogencarbonates react with acids to give a corresponding salt, carbon dioxide and water. Thus, the reaction can be summarised as –

`color{red}(" 𝐌𝐞𝐭𝐚𝐥 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞 / 𝐌𝐞𝐭𝐚𝐥 𝐡𝐲𝐝𝐫𝐨𝐠𝐞𝐧𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞 + 𝐀𝐜𝐢𝐝 → 𝐒𝐚𝐥𝐭 + 𝐂𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 + 𝐖𝐚𝐭𝐞𝐫")`

𝐇𝐲𝐝𝐫𝐨𝐜𝐡𝐥𝐨𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞𝐬 𝐠𝐚𝐬 𝐬𝐨𝐝𝐢𝐮𝐦 𝐜𝐡𝐥𝐨𝐫𝐢𝐝𝐞 𝐚𝐥𝐨𝐧𝐠 𝐰𝐢𝐭𝐡 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐬𝐨𝐝𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("Sodium carbonate")(Na_2CO_3) + underset("Hydrochloric acid")(2HCl) → underset("Sodium chloride")(2NaCl)+ underset("carbon dioxide")(CO_2) + underset("Water")(H_2O))`

𝐇𝐲𝐝𝐫𝐨𝐜𝐡𝐥𝐨𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 , 𝐦𝐚𝐠𝐧𝐞𝐬𝐢𝐮𝐦 𝐜𝐡𝐥𝐨𝐫𝐢𝐝𝐞 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐦𝐚𝐠𝐧𝐞𝐬𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.


`color{red}(underset("Magnesium Carbonate")(MgCO_3) + underset(" Hydrochloric acid")(2HCl) → underset("magnesium chloride")(MgCl_2) + underset("carbon dioxide")(CO_2) + underset("water")(H_2O))`

𝐇𝐲𝐝𝐫𝐨𝐜𝐡𝐥𝐨𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 𝐠𝐚𝐬 , 𝐜𝐚𝐥𝐜𝐢𝐮𝐦 𝐜𝐡𝐥𝐨𝐫𝐢𝐝𝐞 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐜𝐚𝐥𝐜𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.


`color{red}(underset("calcium Carbonate")(CaCO_3) +underset(" Hydrochloric acid")(2HCl) → underset("Calcium Chloride ")(CaCl_2) +underset("carbon dioxide")(CO_2) + underset("water")(H_2O))`

𝐒𝐮𝐥𝐩𝐡𝐮𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐜𝐚𝐥𝐜𝐢𝐮𝐦 𝐬𝐮𝐥𝐩𝐡𝐚𝐭𝐞, 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 𝐠𝐚𝐬 𝐚𝐧𝐝 𝐜𝐚𝐥𝐜𝐢𝐮𝐦 𝐬𝐮𝐥𝐩𝐡𝐚𝐭𝐞 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐜𝐚𝐥𝐜𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("calcium carbonate")(CaCO_3) + underset("Sulphuric acid")(H_2SO_4)→ underset("Calcium sulphate")(CaSO_4) + underset("Carbon dioxide")(CO_2) + underset("water")(H_2O))`

𝐒𝐮𝐥𝐩𝐡𝐮𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐬𝐨𝐝𝐢𝐮𝐦 𝐬𝐮𝐥𝐩𝐡𝐚𝐭𝐞 , 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 𝐠𝐚𝐬 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐬𝐨𝐝𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("sodium carbonate")(Na_2CO_3) + underset("Sulphuric acid ")(H_2SO_4) → underset("sodium Sulphate")(Na_2SO_4) + underset(" Carbon dioxide")(CO_2) + underset("water")(H_2O))`

𝐍𝐢𝐭𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐬𝐨𝐝𝐢𝐮𝐦 𝐧𝐢𝐭𝐫𝐚𝐭𝐞 , 𝐰𝐚𝐭𝐞𝐫 𝐚𝐧𝐝 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 𝐠𝐚𝐬 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐬𝐨𝐝𝐢𝐮𝐦 𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("nitric Acid")(2HNO_3) + underset("Sodium carbonate")(Na_2CO_3) → underset("sodium nitrate")(NaNO_3) + underset("water")(2H_2O) + underset("carbon dioxide")(CO_2))`

𝐇𝐲𝐝𝐫𝐨𝐜𝐡𝐥𝐨𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 , 𝐬𝐨𝐝𝐢𝐮𝐦 𝐜𝐡𝐥𝐨𝐫𝐢𝐝𝐞 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐬𝐨𝐝𝐢𝐮𝐦 𝐛𝐢𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("sodium bicarbonate")(NaHCO_3) + underset("Hydrochloric acid")(HCl) → underset("Sodium chloride")(NaCl) + underset("carbon dioxide")(CO_2) + underset("water')(H_2O))`

𝐒𝐮𝐥𝐩𝐡𝐮𝐫𝐢𝐜 𝐚𝐜𝐢𝐝 𝐠𝐢𝐯𝐞𝐬 𝐬𝐨𝐝𝐢𝐮𝐦 𝐬𝐮𝐥𝐩𝐡𝐚𝐭𝐞 , 𝐜𝐚𝐫𝐛𝐨𝐧 𝐝𝐢𝐨𝐱𝐢𝐝𝐞 𝐠𝐚𝐬 𝐚𝐧𝐝 𝐰𝐚𝐭𝐞𝐫 𝐰𝐡𝐞𝐧 𝐢𝐭 𝐫𝐞𝐚𝐜𝐭𝐬 𝐰𝐢𝐭𝐡 𝐬𝐨𝐝𝐢𝐮𝐦 𝐛𝐢𝐜𝐚𝐫𝐛𝐨𝐧𝐚𝐭𝐞.

`color{red}(underset("Sodium bicarbonate")(2NaHCO_3) + underset("Sulphuric acid")(H_2SO_4) → underset("Sodium sulphate ")(Na_2SO_4) + underset("carbon dioxide")(2CO_2) + underset("water")(2H_2O))`

`color{green}("𝐎𝐁𝐒𝐄𝐑𝐕𝐀𝐓𝐈𝐎𝐍")` - Here the effect of a base is nullified by an acid and vice-versa. The reaction taking place is written as –

`color{red}(NaOH (aq) + HCl (aq) → NaCl (aq) + H_2O(l))`

The reaction between an acid and a base to give a salt and water is known as a neutralisation reaction.

`color{red}(" 𝐁𝐚𝐬𝐞 + 𝐚𝐜𝐢𝐝 → 𝐒𝐚𝐥𝐭 + 𝐖𝐚𝐭𝐞𝐫 ")`

`color{green}("𝐎𝐁𝐒𝐄𝐑𝐕𝐀𝐓𝐈𝐎𝐍:")` Colour of the solution becomes blue-green and the copper oxide dissolves. The blue-green colour of the solution is due to the formation of copper(II) chloride in the reaction. The general reaction between a metal oxide and an acid can be written as –

`color{red}("𝐦𝐞𝐭𝐚𝐥 𝐨𝐱𝐢𝐝𝐞 + 𝐀𝐜𝐢𝐝 → 𝐒𝐚𝐥𝐭 + 𝐰𝐚𝐭𝐞𝐫")`

Since metallic oxides react with acids to give salts and water, similar to the reaction of a base with an acid, metallic oxides are said to be basic oxides.