Explore topic-wise InterviewSolutions in .

• Oxidation is defined as the interaction of oxygen molecules with all the different substances from metal to living tissue which may come into contact with it. 
• When fats and oils are oxidized they become rancid. Their smell and taste change. 
• Keeping food in airtight containers helps to slow down oxidation process. 
• So, manufacturers of potato chips usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidized.

Properties of chemical reaction

• Iron reacts with oxygen and moisture present in the air, forms the iron oxide (rust).
• Production of gas: When fuel like petrol, kerosene etc are burnt then carbon present in them reacts with air and forms (CO₂ ) carbon dioxide in the same manner CO₂ is produced when coal is burnt. C + O → CO₂ (gas)
• When sulphuric acid is poured slowly in a test tube in granulated zinc, hydrogen gas is produced. If a burning matchstick is taken at the mouth of the test tube it burns with an explosion.
• Change in colour: Colour of cut apple is changed because iron present in apple reacts with oxygen present in the air and form iron oxide.
• Change of heat: When ammonium chloride is put in water it becomes cold.
• Dissolution: In hard water, soap does not form foams but produces white undissolved substance.

(c) oxygen or removal of hydrogen

Dissociation reaction- Powder of lime
Calcium carbonate \(\overset{On\,heating}{\longrightarrow}\) Calcium oxide (CaO) → Carbon dioxide (CO₂ ) When lime powder is heated, gas is produced. When it is allowed to blow in lime water, it turns milky. This gas is CO₂ . A reaction in which a reactant decomposes and forms two or more product is called decomposition reaction.

Those reaction in which less reactive element of compound is displaced by more reactive element is called displacement reaction.

When two or more than two elements or compounds combines produces a new product (compound) is called an addition reaction.
Iron (Fe) + Oxygen (O₂ from air) → Iron oxide (Fe₃O₄) 3Fe + 2O₂ → Fe3O₄

Powder of limewater
Calcium carbonate CaCO₃ \(\overset{On\,heating}{\longrightarrow}\) Calcium Oxide CaO → Carbon dioxide CO₂
When lime powder is heated a gas is produced when it is allowed to blow in limewater, it turns milky. This gas is CO₂.

CaCO₃ → CaO + COa

Carbon dioxide (CO₂).

Iron granules and sulphur powder after reaction make a new colour substance iron sulphide.
Iron + sulphur → iron sulphide

Powdered iron burns like fireworks and form oxide of iron.
3Fe + 2O₂ → Fe3O₄

(a) Carbon dioxide present in the atmosphere is trapped by infrared radiations, gives rise to the temperature which is an exothermic reaction.

(b) The melting of glaciers by global warming.

(a) A chemical reaction in which a base or an alkali reacts with an acid to produce a salt and water.

Acid + Base → Salt + Water

(b) Dissolution of ammonium chloride in water is an endothermic reaction in which heat energy is absorbed.

The balanced chemical equation is 

Zn + 2 HCl → ZnCl₂ + H₂ 65 U + (2 × 36.5) U → (65 + 2 × 35.5) U + 2 U 65 g + 73 g → 136 g + 2g 

As per the balanced equation 65 g Zinc is reacting with hydrochloric acid to produce 2g of Hydrogen.

So the amount of Zinc required to produce 500 g hydrogen = 65/2 x500 = 16250 g.

(a) exothermic reaction

The different types of chemical reactions are 

1. Chemical combination 

Ex : S + O₂ → SO₂ 

2. Chemical decomposition 

Ex: 2KMnO₄ → K₂MnO₄+ MnO₂ + O₂ 

3. Chemical displacement 

Ex : Zn + H₂SO₄ → ZnSO₂ + H₂ ↑ 

4. Chemical double decomposition 

Ex : MgSO₄ + Na₂CO₃

 → MgCO₃ + Na₂CO₄

(a) towards reactants

(b) physical change operator

The chemical reactions are mainly of following types based on the nature of reactants and products. 

1. chemical combination 

2. chemical decomposition 

3. chemical displacement 

4. chemical double decomposition or exchange.

Law of conservation of matter or mass states that matter can neither be created nor destroyed.

(c). law of conservation of mass or matter.

The practice of equalizing the number of atoms of atoms of elements on left hand side to the corresponding atoms on right hand side is called balancing of equation.

The electrons which take part in chemical reactions are called valence electrons.

Rusting of iron and combustion of fuels are simple chemical reactions.

‘Photo synthesis’ is a complex chemical reaction.

Plastic is non biodegradable in the nature and causes pollution. Hence the usage of plastic must be avoided or minimized.

The main cause of chemical reaction is the desire of atoms to get stable electronic configuration.

Combustion is an oxidation reaction 2C₄H₁₀ + 16O₂ → 16O₂ 8CO₂ + 10H₂OCO₂ and H,O are the products formed when C₄H₁₀ undergoes complete combustion.

1) Iron reacts with oxygen and forms iron oxide. 

4Fe + 3O₂ → 2Fe₂O₃. 

2) Copper reacts with oxygen and forms copper oxide. 

2Cu + O₂ → 2CuO 

3) Silver tarnishes when reacts with hydrogen sulphide and oxygen 

4Ag + 2H₂S + O₂ → 2Ag₂S + 2H₂O

Some methods to avoid corrosion 

1.  Painting, oiling, greasing on the surfaces of the metals. 
2.  Galvanizing the metal with thin layer of zinc. 
3.  Making alloy metals prevents corrosion, eg : brass, bronze and steel.

Oxidation : 

It is a reaction involving addition of oxygen or removal of hydrogen from a substance. 

1) Magnesium reacts with oxygen to form magnesium oxide. 

2 Mg + O₂ → 2 MgO 

2) Copper reacts with oxygen to form copper oxide.

2 Cu + O₂ → 2 CuO 

3) Iron reacts with oxygen to form ferric oxide. 

4 Fe + 3 O₂ → 2Fe₂O₃

Reduction : 

It is a reaction involving addition of hydrogen or removal of oxygen from a substance. 

1) Nitrogen gas reacts with hydrogen gas to produce Ammonia.

N₂ + 3H₂ → 2NH₂ 

2) Oil reacts with hydrogen to form fat. 

Oil + H₂ → Fat

The reactions in which a substance insoluble in water is formed are called precipitation reactions.

e.g.: 

1) When lead nitrate solution reacts with potassium iodide solution it forms a yellow precipitate of lead iodide. 

Pb(NO₃)_2(aq) + 2KI_(aq) → PbI_2(s) + 2KNO_3(aq)  

2) When sodium sulphate solution reacts with barium chloride solution it forms a white precipitate of barium sulphate. 

Na₂SO4_(aq) + BaCl_2(aq) → BaSO_4(s)+ 2NaCl_(aq)

In the above equation, HCl compound is oxidized and MnO₂ is reduced.

1. A physical change is a temporary change.

2. In a endothermic reaction heat energy is absorbed.

3. In a double decomposition precipitation reaction both the reactants must be water soluble.

4. In a neutralization reaction, an acid reacts with a base to form salt and water as the only products.

5. Distillation is a method of obtaining pure solvant from a solution.

6. On reaction with sulphuric acid solution, barium chloride forms a white precipitate of barium sulphate.

7. Strong electrolytes dissociate completely in aqueous state and allow large amount of electricity to flow through it.

8. Negatively charged ions are called anions.

9. In a chemical change, new substances are formed.

10. The new substances formed during a chemical reaction are called the products.

11. Positively charged ions are called cations.

Miscible liquids having slightly different boiling points can be separated by the fractional distillation.

Reduction is a chemical reaction in which there is removal of oxygen

Compounds, which in their molten state allow an electric current to pass through them are called electrolytes.

Lime water turns milky.

Electrolysis is the process of decomposition of an electrolyte, in its aqueous state by passing direct electric current through it.

On the basis of whether or not a reaction goes to completion, chemical reactions are classified into two categories. 

These are discussed as under:

1. Irreversible reactions: A reaction in which the reactants are completely converted into products is called an irreversible reaction, e.g.

C + O₂ → CO₂

2. Reversible reactions: A reaction which proceeds in both forward and reverse directions is called as a reversible reaction.

e.g. N₂ + 3H₂  ⇌  2NH₃

A metallic substance made by mixing and fusing two or more metals or a metal and a non-metal, to obtain desirable qualities such as hardness, lightness and strength is called alloy. 

Ex : Brass, bronze, steel.

Copper granules become black after heating because outer surface of copper granules is covered with black copper oxide.
CuCO₃ → CuO + CO₂

Oxidizing Agents-Substance which oxidize other substances by providing oxygen to them or by removing hydrogen from them.

Non-electrolyte

Steel, PVC and CPVC pipes are suitable/suggestable for water supply. 

Reasons: 

1.  They are not oxidised in moisture. 
2.  They do not form oxides. 
3.  They are not corroded. 
4.  So, they are durable and safe to use in supply of water.

1. PVC, CPVC and steel pipes are used for water supply in my house. 

2. Because they do not corrode.

The decomposition reaction occurs in the presence of sunlight is called photochemical reaction.

Ex : 2AgBr_(s) → 2Ag_(s) + Br_2(g)

The chemical reaction involved in corrosion of iron is oxidation reaction.