Acids Bases and Salts: Class 7 Science NCERT Chapter 5

Key Features of NCERT Material for Class 7 Science Chapter 5 –   Acids, Bases and Salts

In the last chapter 4, you learned about Heat. In this chapter, you all will learn about Acids, Bases, and Salts.

Quick revision notes

In our every day life, we utilize an enormous number of palatable substances, for example, lemon, preparing pop, tamarind, basic salt, sugar, curd and vinegar. A portion of these substances taste acrid, some taste unpleasant, some taste sweet and some taste pungent. 

Acids, bases and salts are the three significant gatherings of compound substances that are utilized by us in various manners. A portion of the acids, bases and salts happen in nature and they can be made falsely in production lines too.

Edible substances and their tastes

SubstanceTaste (Sour/Bitter/Any other)
Lemon JuiceSour
Orange JuiceSour
Common SaltSalty
Baking SodaBitter

Acids and Bases

The word corrosive has been gotten from a Latin word ‘acidus’ which signifies ‘harsh’. In this way, all sharp substances basically contain acids. Substances like lemon juice, squeezed orange, unripe mango and curd taste acrid. They taste acrid on the grounds that they contain substances called acids in them. The compound idea of such substances is acidic. The acids in these substances are normal acids. 

In any case, there are different substances like preparing soft drink it doesn’t taste acrid. 

It implies that it has no acids in it. It is harsh in taste. Also, if set up an answer of heating soft drink in water and rub it between your fingers, it feels lathery. Substance like these which are harsh in taste and feel sudsy on contact are known as bases. The synthetic idea of such substances is supposed to be fundamental. All the acids referenced in table happen in nature.

Acids and their Sources

Name of AcidFound in
Acetic AcidVinegar
Formic AcidAnt’s Sting
Citric AcidCitrus fruits such as oranges, lemons, etc..
Lactic AcidCurd
Oxalic AcidSpinach
Ascorbic Acid(Vitamin C)Amla, Citrus fruits
Tartaric AcidTamarind, grapes, unripe mangoes, etc..

Bases and their Sources

Name of BaseFound in
Calcium HydroxideLime Water
Ammonium HydroxideWindow Cleaner
Sodium Hydroxide/Potassium HydroxideSoap
Magnesium HydroxideMilk of Magnesia

Natural Indicators Around Us

It isn’t protected to taste each substance to see whether it is acidic or essential. There are some exceptional substances that have various hues in acidic and essential mediums. These substances are known as pointers. The markers change their shading when added to an answer containing an acidic or an essential substance. 

Some normally happening markers are litmus, turmeric, China flower petals (gudhal) and red cabbage juice. These markers show various hues in acidic and fundamental media. They are utilized to test whether a substance is acidic or essential in nature.

Litmus- A Natural Dye

A normally happening marker, for example litmus is acquired from specific lichens (little plants) and utilized as a weaken arrangement. Litmus has mauve (purple) shading in water. In an acidic arrangement, it turns red. At the point when it is added to an essential arrangement, it turns blue. Ordinarily, it is accessible as a red and blue litmus paper. 

Turmeric is Another Natural Indicator 

Turmeric is a splendid yellow powder got from a plant. It is called ‘Haldi’ in Hindi. Turmeric contains a yellow color. Turmeric turns red in essential arrangement. It is utilized as marker as turmeric paper. 

China Rose as an Indicator 

China rose is a characteristic marker. It is called ‘Gudhal’ in Hindi. It is a removed from the red blossoms of China rose plant with water. 

Acid Rain 

The downpour containing overabundance of acids called a corrosive downpour. The downpour becomes acidic on the grounds that carbon dioxide, sulfur dioxide and nitrogen dioxide disintegrate in downpour drops to frame carbonic corrosive, sulphuric corrosive and nitric corrosive individually. It can make harm structures, verifiable landmarks, plants and creatures.

This happens as follows:

  • Corrosive downpour makes the water of lakes, lakes and waterways excessively acidic because of which fish and other sea-going creatures get executed. 
  • Corrosive downpour gobbles up the leaves of the trees progressively. By losing leaves, the trees bite the dust. Corrosive downpour additionally harms crop plants in the fields. 
  • Corrosive downpour harms the metal structures like steel spans, and so on when it falls on them. 
  • Corrosive downpour harms the surfaces of structures and landmarks comprised of marble.


Acids and bases are artificially inverse substances. Thus, when a corrosive is blended in with a base, they kill (or drop) the impact of one another. At the point when a corrosive arrangement and a base arrangement are blended in appropriate sums, both the acidic idea of the corrosive and the fundamental idea of the base are decimated. The subsequent arrangement is neither acidic nor essential. Along these lines, the response between a corrosive and base is known as balance. During the time spent balance, salt and water are delivered with the development of warmth. 

Salt created in the response might be acidic, essential or unbiased in nature. The developed warmth raises the temperature of the response blend. 

Corrosive + Base → Salt + Water (Heat is developed) 

for example Hydrochloric corrosive (HCl) (Acid) + Sodium hydroxide (NaOH) (Base) → Sodium chloride (NaCl) (Salt) + Water (H2O) 

On the off chance that weaken sulphuric corrosive is added to lime water (which is a base), at that point balance response happens and the response blend gets hot. 

We are going to utilize a marker which you have not utilized up until now. It is called phenolphthalein. 

Note: Phenolphthalein is a pointer utilized in the balance cycle. At the point when the arrangement is essential, phenolphthalein gives a pink shading yet in the event that the arrangement is acidic, it stays dry.

Neutralisations in Everyday Life

The balance responses including acids and bases assume a significant job in our regular daily existence. The treatment of a subterranean insect’s sting, solution for acid reflux, soil treatment and the treatment of processing plant squanders, all include balance response. 


Our stomach produces hydrochloric corrosive. This hydrochloric corrosive aides in processing our food. Here and there, abundance of hydrochloric corrosive is created in the stomach which causes acid reflux. Because of acid reflux, some of the time an individual feels torment in the stomach and aggravation. To calm heartburn, we take an acid neutralizer, for example, milk of magnesia. Milk of magnesia contains a base called magnesium hydroxide. Magnesium hydroxide kills the overabundance corrosive present in the stomach and fixes acid reflux. Another acid neutralizer is heating soft drink which contains a base sodium hydrogen carbonate. 

Ant Bite 

At the point when an insect nibbles, it infuses an acidic fluid into the skin of the individual which causes consuming torment. The sting of an insect contains a corrosive called formic corrosive. The impact of the corrosive can be killed by scouring a gentle base like heating soft drink arrangement (sodium hydrogen carbonate) or calamine arrangement. Calamine arrangement contains a base called zinc carbonate. Subsequently, being a base, heating soft drink arrangement or calamine arrangement kills the acidic fluid infused by the subterranean insect and drops its impact. 

Soil Treatment 

The dirt might be acidic or essential normally. The plants don’t develop well, if the dirt at a spot is excessively acidic or excessively fundamental. Exorbitant utilization of substance composts makes the dirt acidic. At the point when the dirt is excessively acidic, it is treated with bases like quicklime (calcium oxide) or slaked lime (calcium hydroxide). These bases kill the abundance corrosive present in the dirt and lessen its acidic nature. In the event that the dirt is fundamental, natural issue called fertilizer or manure is added to it. The natural issue discharges acids which kill the abundance bases present in the dirt and decrease its essential nature. 

Factory Wastes 

The waste substances released by numerous processing plants contain acids. On the off chance that these processing plant squanders are permitted to stream into the water bodies (like waterways, lakes, lakes, and so on), at that point the corrosive present in them will execute fish and different living beings which live in the water bodies. The manufacturing plant squanders are in this way killed by including fundamental substances before releasing them into water bodies.

(Acids Bases and Salts: Class 7)

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