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Acids, Bases and Salts

Acids, Bases and Salts
science Square
Science Square

Substances can be divided into three types –

  • Acids
  • Bases
  • Salts


Acid tastes sour. The substances that contain acid and are sour are lemon, curd, orange juice, pickles, vinegar, etc.

These substances are called as Acidic. The word acid is derived from the Latin word “ACERE" that means sour. 


Base tastes bitter. Substances that have bitter taste are soap solution, baking soda, soap, washing soda, etc.

The substances that contain base and have chemical nature are known as BASIC.

Characteristics of Acid

  • Acid is sour in taste.
  • It converts blue litmus paper into the red.
  • It also converts China rose solution into dark pink color.

Characteristics of Base

  • A base is bitter in taste.
  • It converts red litmus paper into blue color.
  • It turns china rose solution into green color


Understanding whether the nature of substances is acidic or basic cannot always be understood by tasting them. Tasting in a laboratory is also harmful thus for this purpose a special substance is used called an indicator.

It is a substance that tells about the acidic or basic nature of a particle only by changing the color.

Science Class 7 Acids, Bases and Salts Indicator

  1. Natural Indicator – When the indicators are obtained from the naturally occurring substances than they are known as Natural Indicators. For example – China rose, litmus, turmeric, etc.
  2. Synthetic Indicator – When the indicators are made in the laboratory then they are called as synthetic indicators. For example – methyl orange, phenolphthalein, etc.

Acid rain

When carbon dioxide, nitrogen dioxide and sulphur dioxide are released from vehicles then mix with the rain droplets and turn it too acidic. The rainwater becomes acidic and when the rain falls it is called as acid rain. Acid rain is harmful to buildings and plants and animals. Acid rain has also affected Taj Mahal.

Science Class 7 Acids, Bases and Salts Acid rain



When solutions of acid and base are mixed then they both neutralize each other and form a third substance called SALT. This process is known as neutralization. The solution of salt is neither acidic nor basic and hence called as a neutral solution.

When a base called sodium hydroxide is mixed with hydrochloric acid then they form a common salt called as sodium chloride.

Sodium Hydroxide + Hydrochloric acid Sodium chloride + Water

(Solution Solution Solution Liquid)

Neutralization in Soil Treatment

Due to the more use of fertilizers or incorrect use of harvesting methods, the soil becomes acidic or basic. It affects the growth of plants. Then quicklime and slaked lime are used with Acidic soil to nullify the acidic nature of the soil. In case of basic soil, it is combined with organic matter.

Science Class 7 Acids, Bases and Salts Neutralization 


  • Acids are sour in taste and bases are bitter.
  • There are three types of substances-
  •  Acid
  • Base
  • Salt
  • Salts are formed when with the combination of Acids and Bases. This process is called as Neutralization.
  • The two types of Indicators are –
  • Natural Indicators
  • Synthetic Indicators


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Quiz for Acids, Bases and Salts


The root of the word "acid" comes from the Latin word-










Name the acid found in this substance.



Oxalic acid


Lactic acid


Citric acid


Acetic acid


Which of the following are not natural indicators?

a) litmus
b) china rose petals
c) turmeric
d) none of the above


A solution is found to have a pH 2, it is a-


strong base


weak base




strong acid


Dry hydrogen chloride gas does not turn blue litmus, whereas hydrochloric acid does. Why?

a) Because it cannot behave as an acid
b) It does not release H+ ions
c) Both (a) and (b)
d) None of the above


In one of the industrial process used for manufacture of sodium hydroxide, a gas ‘X’ is formed as by – product. The gas ‘X’ reacts with lime water to give a compound calcium oxy chloride which is used as a bleaching agent in chemical industry. Identify ‘X’.

a) CO₂
b) Cl₂
c) H₂
d) O₂


10 ml of a solution of NaOH is found to be completely neutralized by 8 ml of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount of HCl solution required to neutralize it will be

a) 4 ml
b) 8 ml
c) 12 ml
d) 16 ml


When acids are dissolved in water they produce ions which help in conducting the electricity. This process is known as—

a) Dissociation
b) Vulcanization
c) Galvanization
d) Sublimation


When turmeric stain on white clothes is washed with soap, it turns red in color because _______.

a) Soap solution is acidic
b) Soap solution is neutral
c) Both (a) & (b)
d) Soap solution is basic


How is the concentration of hydronium ions (H₃O+) affected when a solution of an acid is diluted?

a) Strength increases
b) Per unit volume increases
c) Per unit volume decreases
d) None of the above

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