Chemical Weathering- NCERT Geography Notes For UPSC Exams

Beny Basumatary | Updated: Jun 17, 2021 10:41 IST

NCERT Notes: Chemical weathering is one among important topics for UPSC Civil Services  exam. In this article we will be covering what is weathering, chemical weathering along with its solution. By keeping all these things in mind, Testbook prepares the best quality notes for you to study. These notes are useful for other exams also like banking PO, SSC, state civil services exams and so on.

  • Action of different elements of weather and climate on the Earth material is called weathering.
  • This weathering process can be done in numerous ways. During this process earth material is broken down into small fragments. Weathering process is further grouped into three types and one among them is biological weathering.
  • A process of weathering which occurs via: solution, carbonation, hydration, oxidation and reduction process is called chemical weathering. All these processes are done on rocks to decompose, dissolve or reduce them into smaller fragments
  • All these chemical reactions involve  oxygen, surface and/or soil water and other acids. In these processes air i.e. oxygen and Carbon dioxide along with heat play major roles in speeding up the chemical process.

Chemical Weathering (UPSC Geography) NCERT Notes: Download PDF Here

  • Chemical Weathering: Types of Process
    • Solution
    • Carbonation
    • Hydration
    • Oxidation and Reduction
  • Chemical Weathering FAQs

Chemical Weathering: Types of Process

In the process of chemical weathering, rocks and minerals react  to acids, oxygen, carbon and water which leads to formation of unique rocks and caves, one of the most awestrucking structures in the world.Chemical weathering causes nifty formations, the way it breaks down rocks by the processes of carbonation, oxidation, hydration, hydrolysis and acidification work which causes fractures in ancient structures like the Great Sphinx of Egypt. It also causes the surface to break down to  gravestones.

Solution

  • When any substance i.e. solute is dissolved in water or acids i.e. solvent, then water or acids with dissolved content is termed as solution.
  • In this weathering process removal of solids is done by solution. This removal process depends upon solubility of a mineral in water or weak acids. As when solids come in contact with solution they disintegrate into smaller particles and get mixed with water as suspension.
  • Minerals like: nitrates, sulphates, and potassium etc. are known to be soluble rock forming minerals as they get affected by this process. All these minerals easily get dissolved in water. Whereas minerals like Calcium carbonate and Calcium magnesium are dissolved in that water only which contain carbonic acid also.
  • All these minerals are very easily leached without leaving any residue in rainy climates and further get accumulated in dry areas.
  • There are few minerals i.e. calcium carbonate and calcium magnesium bicarbonate which are present in limestone are soluble in that water which have carbonic acid in its composition. They are also carried away by water as a solution.
  • During decomposition of organic matter carbon dioxide is released along soil water and it also assists this chemical reaction process.

Check NCERT notes on Weathering here.

Carbonation

  • The reaction which involves carbonate and bicarbonate with minerals is called the carbonation process. This process is helpful in breaking down fields of feldspars and carbonate minerals.
  • It involves absorption of carbon dioxide from atmosphere and soil air by water for the formation of carbonic acid which is a weak acid. Further calcium carbonates and magnesium carbonates are dissolved in carbonic acid.
  •  They are  removed in a solution without leaving any residue and forming a cave.

You might also like: NCERT notes on Physical Weathering

Hydration

  • The process of chemical addition of water is called hydration. In this process minerals absorb water and get expanded.
  • This expansion leads to an increase in volume of the material or rock.
  • Compounds like calcium sulphate take water and for gypsum. This process is reversible in nature. If this process is continued for a long time and keeps on repeating then this process causes fatigue in the rocks and may lead to their disintegration.
  • Many clay minerals get swelled up and contract as they wet or dry and repetition of this process causes cracking of overlying materials.
  • Pores present in salts undergo a rapid and repeated hydration process which helps rocks to fracture.
  • Change in volume of minerals because of the hydration process will also help in the physical weathering process through exfoliation and granular disintegration.

Oxidation and Reduction

  • Process of combining minerals with oxygen for the formation of oxides and hydroxides is called oxidation during weathering. This process occurs only when there is ready access to the atmosphere and oxygenated waters.
  • The minerals which are frequently involved in this process are iron,manganese, sulphur etc.
  • During the process of oxidation of rock, their breakdown occurs because of the  disturbance created due to the addition of oxygen.
  • Red colour of iron during the oxidation process turns to brown or yellow color.
  • Process of reduction occurs when oxidised minerals are placed in an environment in the absence of oxygen. This condition is seen below the water table, in areas of stagnant water and waterlogged ground.
  • During the reduction process the red color of iron turns into green or bluish grey.

Also read: NCERT notes on Biological Weathering

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Chemical Weathering FAQs

Q.1 Why physical and chemical weathering are interdependent from each other?

Ans.1

Physical and chemical weathering are considered to be simultaneous and interdependent on each other because during the physical weathering process degradation of rocks occurs due to physical forces like wind,air,sunlight,rain whereas in Chemical weathering degradation occurs due to chemicals, which may be naturally(HCl) or biologically occurring.

Q.2 What are the differences present between physical and chemical weathering?

Ans.2

In this process physical disintegration of rock takes place while in the chemical disintegration of rock takes place.

Q.3 What are the factor which work behind the chemical weathering process?

Ans.3

Chemical weathering process occurs when rainwater reacts with the mineral grains in rocks to form new minerals (clays) and soluble salts. Slightly acidic water is favourable for the chemical weathering process.

Q.4 What is the name of different agents which are majorly involved in chemical weathering?

Ans.4

One of the major agents involved in chemical weathering is water along with carbon dioxide and oxygen.

Q.5 What are the different types of chemical weathering?

Ans.5

Different types of chemical weathering processes are solution, hydration, hydrolysis, carbonation, oxidation, reduction, and chelation.

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