Acids, Bases and Salts (Indicators) : Science CBSE Notes
Many substances that you encounter in your daily life have different properties. One major difference between substances is whether they are acidic or basic.
- Acidic substances taste sour. Some examples are curd, lemon juice, tamarind, spinach and vinegar. These contain natural acids.
- Basic substances taste bitter and feel slippery to the touch. Some examples are baking soda and milk of magnesia.
There are special substances that are used to test whether something is acidic or basic. These substances are called indicators. Indicators change their colour when added to an acidic or basic solution. Some natural indicators are litmus, turmeric and china rose petals.
- Litmus is a natural dye extracted from lichens. It is the most commonly used natural indicator.A solution of litmus turns red if it is acidic, and blue if it is basic.
Litmus has a purple colour in a neutral medium, red colour in an acidic medium, and blue in a basic medium.When a drop of freshly prepared lemon juice is put on red litmus, it remains red, indicating the acidic nature of lemon juice.
If blue litmus is used instead, then it turns red, again indicating the acidic nature of lemon juice.
- Turmeric changes colour to indicate acidic and basic substances. It is yellow in acids and reddish brown in basic solutions.
Turmeric paper changes colour in a basic medium.
In an acidic medium, it remains yellow, while in a basic medium, it turns reddish brown.
When a drop of soap solution is put on turmeric paper, it turns red. This indicates the basic nature of soap solution.
|S. No||Test solution||Effect on turmeric paper|
|3||Lime water||Reddish brown|
|4||Milk of magnesia||Reddish brown|
|S. No||Name of acid /base||Effect on litmus paper||Effect on turmeric paper|
|1||Hydrochloric acid||Blue litmus turns red||Remains yellow|
|2||Sulphuric acid||Blue litmus turns red||Remains yellow|
|3||Sodium hydroxide||Red litmus turns blue||Turns reddish brown|
|4||Potassium hydroxide||Red litmus turns blue||Turns reddish brown|
- China rose is also a natural indicator. A solution of china rose turns green in a basic solution, and bright pink or magenta in an acidic solution.
China rose is another indicator extracted from China rose petals. In an acidic medium, it exhibits dark pink (magenta), while in a basic medium, it exhibits green colour.
|S. No||Name of the acid||Effect on China rose|
|1||Hydrochloric acid||Dark red|
|2||Sulphuric acid||Dark red|
Acid rain is rain that contains a lot of acid. This acid is created when pollutants in the air, such as carbon dioxide, sulphur dioxide and nitrogen dioxide, dissolve in rainwater, and form acids like carbonic acid, sulphuric acid and nitric acid
This rain causes a lot of damage to buildings, plants and animals. This is one important reason why we must avoid polluting our atmosphere.
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