Redox Reactions - Oxidation and Reduction

Chemistry : Class 10

Concept:- Redox Reactions

There are basically two phenomena, related to addition and removal of oxygen and hydrogen. These two are one of the most basic, and important reactions that we come across in our daily lives.

These Reactions are namely:

• Oxidation
• Reduction

It might seem quite easy to learn these reactions, but actually is quite confusing. This picture may help in learning the concept better.

Click to enlarge the image.

Think of Oxidation as a good thing, and reduction as a bad thing. Also, think of oxygen as a good thing, and hydrogen and electrons, as bad things.

So, adding oxygen is a good thing, so the process becomes Oxidation.

Similarly, adding hydrogen is a bad thing, so the process is Reduction.

On the other hand, removing oxygen is a bad thing, so the process is Reduction.

Removing, hydrogen is a good thing, so the process is Oxidation.

It might seem quite confusing, but if you make your fundamentals strong, then its pretty easy.

Lets look at some reactions .

ZnO + C → Zn +CO

Here, ZnO looses oxygen(which is a bad thing) , hence, ZnO is being reduced.

Carbon, gains oxygen(good thing), therefore Carbon is being oxidised.

Can do this reaction. Find the substance oxidised, and the substance reduced.

MnO2 + 4HCl --> MnCl2 + 2H2O + Cl2

Those reactions, in which oxidation and reduction reactions occur simultaneously, are called Redox reactions.

Below is a redox reaction, where, Iron is oxidised. The oxygen comes from kMnO4.

Another example of redox reaction, is Iron with copper sulphate which you have already studied in displacement reaction,

Applications of Redox reactions:-

Corrosion

Rusting of iron, in humidity and moisture is an example of redox reaction, in which Iron is being oxidised. The formula for rust is Fe2O3.10H2O

the 10 H2O molecules, are called water of crystallization.These water molecules, take up spaces present between iron lattice crystals /9between iron atoms).

To prevent rust some measures are taken:

• Painting
• Oiling
• Greasing
• Galvanisation
• Anodising

Can you come across other preventive measures.??

Rancidity

Oxidation of fats and oils present in food stuff, also is a type of redox reaction. If you leave a cut apple for some time, then you shall observe brown coloring over the apple. This brown color is nothing but oxidation of Iron present in the apple.

Have you imagined, why Kurkure or other chip packets are flushed with gas?? This gas is Nitrogen, which is an anti-oxidant. It prevents oxidation of chips, otherwise you won't pay to the shopkeeper for non-crispy chips. Would you??

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Double Displacement Reaction

Chemistry

Concept:- Double Displacement Reaction

You, must have known about Displacement reaction uptil now. In displacement reaction, there was a single element displacing another element which was less reactive.

As, the name suggests, in a double displacement reaction, two elements will displace each other simultaneously. That is why the name,"double displacement reaction", as two displacement reactions are taking place simultaneously.

Example-

Na2SO4(aq) + BaCl2(aq) → BaSO4(s)(ppt) + 2NaCl(aq)

In the above reaction, Na and Ba displace each other simultaneously.

Note:-

In the above reaction, BaSO4, one of the product formed is found to be insoluble in water. Any insoluble salt formed is called a precipitate. Hence, the above reaction is also called a precipitation reaction, due to the formation of an Insoluble precipitate.

In the above video, the white cloudy precipitate is Barium Sulphate, which is an insoluble precipitate.

Another precipitation reaction is shown below.

Some more reactions of precipitation reactions are shown below.

The yellow color lead iodide precipitate formed, is also known as golden rain.

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Heterotrophic Nutrition

Biology

Concept: Heterotrophic Nutrition

The mode of nutrition in which organisms depend on either auto trophs or other heterotrophs, for food, is called heterotropic nutrition.

Example:- Humans, Tigers (all animals).

There are several steps by which heterotropic organism takes nutrition and derives energy:

1. Ingestion
2. Digestion
3. Absorption
4. Assimilation
5. Egestion

The following video will illustrate how some organisms take in food to derive energy from it.

Amoeba

Vorticella

Paramecium

Hydra

Amphibians

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Tooth Decay

Biology

Concept: Tooth Decay

Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins

when bacteria acting on sugars produce acids that softens or demineralises the enamel.

Masses of bacterial cells together with food particles stick to the teeth to form dental

plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers

the teeth. Brushing the teeth after eating removes the plaque before the bacteria

produce acids. If untreated, microorganisms may invade the pulp, causing

inflammation and infection.

So, to prevent, going to the dentist, and taking that pain, basic toothpastes must be used, that keep the pH of mouth OK, and prevent bacteria from flourishing.

Tooth decay may also start when the pH of mouth drops less than 5.5. In this acidic pH, bacteria start multiplying, and create acids, which further degrade the tooth enamel.

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Human Digestion

Biology

Concept: Human Digestion

Humans take nutrition, by taking in food from the mouth. Teeth present in the mouth crush the food into smaller particles and mixed with saliva so as to make the food soft. Saliva , released from the salivary glands, contains salivary amylase which is an enzyme that helps digest starch.

The food then enters into the oesophagus (food pipe), through which the food moves down the elimentary canal due to muscular movement called Peristalsis.

Peristalsis

The rhythemic movement of the muscles of alimentary canal, due to which the food starts moving slowly is called Peristalsis. This occurs slowly so that majority of nutrients may be extracted from the food we eat. The reverse of this process is called Reverse Peristalsis or simply vomitting.

The video below shows the entire process of digetion. Kindly watch carefully. Follow the path of food as it moves down the alimentary canal.

Another video, that would be helpful to you.

Hope you have followed the path of food from the buccal cavity to the anus. Lets recap the events of human digestion quickly.

• food enters the buccal cavity
• food crushed by teeth into smaller units
• particles are mixed with saliva, which digests starch and converts it into glucose.
• the food, mixed with saliva, moves down the alimentary canal through peristalsis.
• in the stomach, pepsin enzyme starts the digestion of protein, facilitated by HCl.
• the food enters the small intestine which recieves gastric secretions from liver, pancrease and gall bladder.
• complete digestion of food takes place in small intestine .
• The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.
• carbohydrate - glucose, protein- amino acid, fats - fatty acid and glycerol
• these basic sub-units are absorbed by tiny finger like projections called villi and tranfered to various cells of the human body through the blood stream.
• the remaining food in the intestine is transfered to colon(large intestine) where water is absorbed
• the final waste is excreted out of the body through anus.

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Autotrophic Nutrition - Photosynthesis

Biology

Concept: Autotrophic Nutrition - Photosynthesis

Carbon and energy requirements of the autotrophic organism are

fulfilled by photosynthesis. It is the process by which autotrophs take

in substances from the outside and convert them into stored forms of

energy. This material is taken in the form of carbon dioxide and water

which is converted into carbohydrates in the presence of sunlight and

chlorophyll.

The excess of carbohydrate produced in plants is converted into starch and stored or transported throughout the plant body. In animals(human beings) the food which is not used is stored as glycogen, which gives rise to obesity. So, the next time you see a fat person, just remember, that he eats the same as you do, but he only does''nt use it as you do.

Raw materials required for Photosynthesis to occur:

• CO2
• Sunlight
• Water
• Chlorophyll

Steps involved in the process of photosynthesis:

• Absorption of light energy by chlorophyll.
• Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
• Reduction of carbon dioxide to carbohydrates.

The above steps when performed during the day, are called Light Reactions.

Desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon

by the energy absorbed by the chlorophyll during the day. Such reactions are called Dark Reactions.

Summary of the above concept:-

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Stomatal opening and closing

Biology

Concept: Stomatal Opening and closing.

Stomata are tiny pores present on the surface of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis. But it is important to note here that exchange of gases occurs across the surface of stems, roots and leaves as well.

Since large amounts of water can also be lost through these stomata, the plant closes these pores when it does not need carbon dioxide for photosynthesis. The opening and closing of the pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink.

Some Plants receive less water from the environment, hence they cannot afford to loose much water through transpiration. That is why they adapt themselves to the scarcity of water.

Such plants which adapt themselves to loose less water, are called Xerophytes. Example:- Cactus.

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Reflex Arc

Biology
Concept: Reflex Arc

Reflex arc is the pathway through which the nerve impulse (generated due to the stimulus )travels throughout the nerves. The receptors gather stimulus and convert them into electrical impulse . This electrical impulse travels through sensory nerve to reach the spinal cord. Spinal cord processes the impulse quickly through relay neuron and then replies through the motor nerve, which affects the effector organ.

This entire process is very fast, so fast that we don't even realize when the reaction started and when it finished.



Touching a flame is an urgent and dangerous situation for us, or in fact, for any
animal! How would we respond to this? One seemingly simple way is to
think consciously about the pain and the possibility of getting burnt,
and therefore move our hand. An important question then is, how long
will it take us to think all this? Actually we do not have enough time to think and react. If we think before acting, we wont have enough time to save our hand from burning.

Therefore, actions which require urgent attention, cannot be carried out by brain directly. These involuntary actions (without our will) are called Reflex Actions. Although, after the reflex action has been completed, the brain realizes and acts accordingly. Like we react by saying "Oh! that was too hot". Saying these words are a function of brain, as they have come after much thought. But the reflex action itself isn't a function of brain.

So we conclude that, all stimuluses pass through spinal cord, while on their way to brain. Only those impulses which require urgent attention, are taken care by the spinal cord (through reflex arc) the rest are done by brain only.

Some Other Examples of Reflex Actions that occur in our daily lives:

Here in the above video, the knee jerk is a result of reflex action, the movement of her leg is unintentional, it is involuntary.



Similarly, when bright light is focussed on the eye, the pupil will constrict, so as to avoid damage to the retina because of excess light. This is not in our control so it is a reflex action.

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Displacement Reaction

Chemistry
Concept:Displacement Reaction

The reaction in which an element, displaces another element from its compound, is called Displacement Reaction. The element that displaces, is more reactive than the element being displaced.

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) (1.24)
(Copper sulphate) (Iron sulphate)
In this reaction, iron has displaced or removed another element,
copper, from copper sulphate solution.




Other examples of displacement reactions are
Zn(s) + CuSO4(aq)→ ZnSO4(aq) + Cu(s) (1.25)
(Copper sulphate) (Zinc sulphate)
Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s) (1.26)
(Copper chloride) (Lead chloride)
Zinc and lead are more reactive elements than copper. They displace
copper from its compounds.

Displacement reactions are carried out to make a series of metals according to their reactivity. This is called Reactivity series.

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Decomposition Reaction

Chemistry
Concept:-Decomposition reaction

A reaction in which, a single reactant, breaks down/decomposes to form two or many products is called Decomposition Reaction.

2FeSO4(s) -heat→ Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous sulphate) (Ferric oxide)
In this reaction you can observe that a single reactant breaks down
to give simpler products. This is a decomposition reaction. Ferrous
sulphate crystals (FeSO4, 7H2O) lose water when heated and the colour
of the crystals changes. It then decomposes to ferric oxide (Fe2O3),
sulphur dioxide (SO2) and sulphur trioxide (SO3).


Decomposition of calcium carbonate to calcium oxide and carbon
dioxide on heating is an important decomposition reaction used in
various industries. Calcium oxide is called lime or quick lime. It has
many uses – one is in the manufacture of cement. When a decomposition
reaction is carried out by heating, it is called thermal decomposition.

CaCO3(s) -Heat→ CaO(s) + CO2(g)




Decomposition of Silver Bromide

2AgBr(s) -Sunlight→2Ag(s) + Br2(g)

Light energy is required to decompose silver bromide. This reaction is called Photo Chemical Decomposition.
The above reactions are used in black and white photography.

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Combination Reaction

Chemistry
Concept:- Combination Reaction

A reaction in which two or more reactants, combine to form a single product, is called Combination Reaction.

Example:

Calcium oxide reacts vigorously with water to produce slaked lime
(calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2(aq)




A solution of slaked lime produced by the reaction is used for white washing
walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin
layer of calcium carbonate on the walls. Calcium carbonate is formed after two to
three days of white washing and gives a shiny finish to the walls. It is interesting to
note that the chemical formula for marble is also CaCO3.

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)



The heat evolved in the above reaction is very large. Reactions in which heat is
released along with the formation of products are called exothermic
chemical reactions.
Other examples of exothermic reactions are –
(i) Burning of natural gas
CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)


Respiration is an Exothermic Process

Respiration involves the breakdown of complex food into simple forms. During digestion,the food we eat is broken down into simpler
substances. For example, rice, potatoes and bread contain
carbohydrates. These carbohydrates are broken down to form glucose.
This glucose combines with oxygen in the cells of our body and provides
energy. The energy is released in the from of heat. hence, respiration is also an exothermic reaction.

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Chemical Reactions

Chemistry
Concept: Chemical Reactions

What is a reaction:

You see numerous reactions around you everyday. Like the making of Rajma! Yes, the making of rajma for lunch or dinner is also an example of a reaction.





Similarly, when chemical elements are involved in a reaction, the reaction is called a Chemical Reaction.

Definition:-
The process in which reactants combine/react to form products is called Chemical Reaction. Reactants are present on the LHS and products formed are represented on the RHS . The reaction rate is shown by an arrow, which indicated the direction of the reaction.

Example:-

Magnesium + Oxygen → Magnesium oxide

Mg + O2 → MgO

The substances that undergo chemical change in the above reaction,
magnesium and oxygen, are the reactants. The new substance,
magnesium oxide, formed during the reaction, is the product.

Click below to see the above reaction, burning of a magnesium ribbon.

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