Science history 28 October

 October 28:

• 1703 – Birth of Antoine Deparcieux, French mathematician (d. 1768)

• 1703 – Death of John Wallis, English mathematician (b. 1616)

• 1792 – Death of Paul Möhring, German physician and scientist (b. 1710)

• 1804 – Birth of Pierre François Verhulst, Belgian mathematician (d. 1849)

• 1841 – Death of Johan August Arfwedson, Swedish chemist (b. 1792)

• 1845 – Birth of Zygmunt Florenty Wróblewski, Polish physicist (d. 1888)

• 1877 – Death of Robert Swinhoe, British naturalist (b. 1835)

• 1914 – Birth of Jonas Salk, American biologist and physician (d. 1995)

• 1914 – Birth of Richard Laurence Millington Synge, Nobel laureate (d. 1994)

• 1918 – Death of Ulisse Dini, Italian mathematician (b. 1845)

• 1957 – Death of Ernst Gräfenberg, German physician and scientist (b. 1881)

• 1960 – Birth of Landon Curt Noll, Astronomer, Cryptographer and Mathematician: youngest to hold the world record for the largest known prime 3 times

• 1970 - Gary Gabelich sets a land speed record in a rocket-powered automobile called the Blue Flame, fueled with natural gas

• 2005 – Death of Richard Smalley, American chemist, Nobel Prize laureate (b. 1943)

All details are from Wikipedia 

Corrosion // Rusting of iron

 Corrosion 

      It is the slow process of eating away metals by the reaction of atmospheric air and moisture, e.g. rusting of iron, formation of green coating over copper etc.

PREVENTION OF CORROSION

     Rusting of iron is prevented by galvanising, by making alloys, painting, greasing or oiling and tin-plating and chrome plating . Explained below --

1. Galvanisation - It is the process of coating iron and steel object with a thin layer of zinc. It is done by dipping the object in molten zinc. The galvanised article is protected against rusting even if the zinc coating is broken.

2. Alloying - It is the method of improving the properties of a metal by mixing the metal with another metal or non-metal.

3. Alloying of iron - Pure iron is very soft and stretches easilywhen hot. It is mixed with a small amount of carbon and it becomes hard and strong. Iron is mixed with many metals to form different types of alloys. For example, when iron is mixed with nickel and chromium, stainless steel is obtained which is hard and does not rust.

4. Painting - Rusting of iron can be easily prevented by coating the surface with a paint which protects iron from air and moisture.

5. Greasing or Oiling - When grease or oil is applied to the surface of iron object then air and moisture cannot be come in contact with it and hence rust is prevented. Thus greasing or oiling prevent from rusting of iron.

6. Tin plating and Chromium Plating - Tin and Chromium metals are resistant to corrosion. So when a thin layer of tin metal is applied on iron object by electroplating then iron and steel objects are protected from rusting. 

सरस्वती वन्दना (हे स्वर की देवी माँ )

 सरस्वती वंदना 

हे स्वर की देवी माँ, वाणी में मधुरता दो ।

हम गीत सुनाते हैं, संगीत की शिक्षा दो ।।

 हे स्वर की देवी माँ, वाणी में मधुरता दो ।

अज्ञान ग्रसित होकर, क्या गीत सुनाएं हम ।

टूटे हुए शब्दों से, क्या स्वर को सुनाएं हम ।।

 हे स्वर की देवी माँ, वाणी में मधुरता दो ।

दो ज्ञान राग माँ तुम, वाणी में मधुरता दो ।

सरगम का ज्ञान नहीं, शब्दों में सार नहीं ।।

 हे स्वर की देवी माँ, वाणी में मधुरता दो ।

तुम्हें आज सुनाने को, मेरी मैया कुछ भी नहीं ।

संगीत समंदर से, स्वर ताल हमें दे दो ।।

 हे स्वर की देवी माँ, वाणी में मधुरता दो ।

भक्ति ना शक्ति है, शब्दों का ज्ञान नहीं ।

गीतों के खजाने से, एक गीत हमें दे दो ।।

हे स्वर की देवी माँ, वाणी में मधुरता दो ।

हम गीत सुनाते हैं, संगीत की शिक्षा दो ।।

प्रार्थना ( वह शक्ति हमें दो दयानिधे )

 

*-------*

वह शक्ति हमें दो दयानिधे ,

                           कर्तव्य मार्ग पर डट जावें ।

पर सेवा पर उपकार में हम ,

                          जग जीवन सफल बना जावें ।

हम दीन दुखी निबलों विकलों ,

                         के सेवक बन संताप हरें ।

जो हैं अटके भूले भटके ,

                        उनको तारें, खुद तर जावें ।

छल दम्भ द्वेष पाखंड झूठ ,

                      अन्याय से निशि दिन दूर रहें ।

जीवन हो शुद्ध सरल अपना ,

                     सुचि प्रेम सुधा रस बरसावे ।

निज आन मान मर्यादा का ,

                   प्रभु ध्यान रहे, अभिमान रहे ।

जिस देश जाति में जन्म लिया,

                  बलिदान उसी पर हो जावें ।

सरस्वती वंदना (रविरुद्र पितामह विष्णुनुतं )

 

रविरुद्र पितामह विष्णुनुतं ।

हरिचंदन कुंकुंम पंकयुतं ।।

मुनिवृन्द गणेन्द्र समानयुतं ।

तव नौमी सरस्वती पादयुगं ।।

शशि शुद्ध सुधा हिम धाम युतं ।

शरदम्बर बिम्ब समान करं ।।

बहुरत्न मनोहर कान्तियुतं ।

तव नौमी सरस्वती पादयुगं ।।

कनकाब्ज विभूषित भूति भवं ।

भव भाव विभाषित भिन्न पदं ।।

प्रभुचित समाहित साधु पदं ।

तव नौमी सरस्वती पादयुगं ।।

भवसागर मज्जन भीतिनुतं ।

प्रतिपादित संततिकारमिदं ।।

विमलादिक शुद्ध विशुद्ध पदं ।

तव नौमी सरस्वती पादयुगं ।।

मतिहीन जनाश्रय पादमिदं ।

सकलागमभाषित भिन्न पदं ।।

परिपूरित विश्वमनेकभवं ।

तव नौमी सरस्वती पादयुगं ।।

परिपूर्णमनोरथ धामनिधिम ।

परमार्थ विचार विवेक निधिम ।।

सुरयोषित सेवित पादतलं ।

तव नौमी सरस्वती पादयुगं ।।

सुरमौली मणिद्युति शुभ्रकर ।

विषयादि महाभय वर्णहरं ।।

निजकान्ति विलेपित चंद्र शिवं।

तव नौमी सरस्वती पादयुगं ।।

गुणनैक कुलस्थिति भीतिपदं ।

गुण गौरव गर्वित सत्यपदं ।।

कमलोदर कोमल पादतलं ।

तव नौमी सरस्वती पादयुगं ।।

Chemical Reactions and Equations (Class 10 Science) Part 3

 

Types of chemical reaction

The chemical reaction are classified into different classes depending upon the type of chemocal changes taking place. These reactions are as follows :

 

1.  Combination Reaction :-

          A reaction in which two or more reactants combine to form a single product, is called combination reaction, e.g.

 

CaO_(s) + H₂O_(l) → Ca(OH)_2(aq) + Heat

 

C_(s) + O_2(g)   →   CO_2(g)

 

2.  Decomposition Reaction :-

          A reaction in which a single reactants breaks down to form two or more products, is known as decomposition reaction. This reaction is opposite to combination reaction. e.g.

CaCO_3(s)  →  CaO_(s)  +  CO_2(g)

 

2AgCl_(s)  →  2Ag_(s) +  Cl_2(g)

 

2NaCl_(l)  →  2Na_(s)  +  Cl_2(g)

 

 

3.  Exothermic and Endothermic reaction :-

          Depending upon whether heat is evolved or absorbed during a reaction, the reaction can be exothermic or endothermic.

(i)Exothermic reactions :-  The reaction which are accompanied by the evolution of heat, are called exothermic reactions or the reaction in which heat is released along with the formation of products are called exothermic reaction. e.g.

a)    Burning of natural gas

CH_4(g)  +  2O_2(g)  →  CO_2(g)

b)   Burning of Magnesium ribbon

2Mg_(s) + O_2(g)  →  2MgO_(s)  +  Heat

(ii)     Endothermic reaction :-  The reaction which occur by the absorption of heat/energy are called endothermic reactions. e.g.

6CO_2(aq)  +  12H₂O_(l)  →  C₆H₁₂O₆ + 6O₂ + 6H₂O

NH₄Cl_(s) + Heat → NH_3(g)  +  HCl_(g)

 

4.  Displacement reaction :-

          When a more reactive element displaces less reactive elwmwnt from its compound, it is called displacement reaction. this reaction is of two types :

(i)    Single displacement reaction :  It is a type of chemical reaction where an element reacts with a compound and takes the place of another element in that compound is called single displacement.

        Zn_(s)   +  CuSO_4(aq)  →  ZnSO_4(aq)  +  Cu_(s)

(ii)    Double displacement reaction :  The reaction in which two different ions or group of atoms in the reactant molecule are displaced by each other is called double displacement reaction.

Na₂SO_4(aq) + BaCl_2(aq)  →  BaSO_4(s)  +  2NaCl_(aq)

 

5.  Oxidation and Reduction reaction :-

OXIDATION :

          It can be defined as

The process in which oxygen is added to a substance.

Or

The process in which hydrogen is removed from a substance.

Or

The process in which a substance loss electrons.

e.g.

2H₂S  +  O₂  →  2S  +  2H₂O

2Cu  +  O₂  →  2CuO

 

REDUCTION :

          It can be defined as

The process in which oxygen is removed from a substance.

Or

The process in which hydrogen is added to a substance.

Or

The process in which a substance gains electrons.

e.g.

2Na  +  H₂  →  2NaH

Zn₂+  +  2^e−  →  Zn

 

Oxidising agents :  The substance which can bring about oxidation of other substances is called an oxidising agent.

Reduction agent :  The substance which can bring about reduction of other substance is called a reducing agent.

 

Redox Reaction :-

          Those reaction in which oxidation and reduction take place simultaneously, are called redox reactions. e.g.

CuO  +  H₂  →  Cu  +  H₂O

          In this reaction the copper oxide is losing oxygen and is being reduced. Whereas oxygen is added to hydrogen and is being oxidised.

 

 

 Corrosion 

          The phenomenon due to which open surface of the metals are slowly eaten away by the reaction of air, water, and chemicals present in the atmosphere is called corrosion.

e.g. Iron articles are shiny when new, but get coated with a reddish brown powder when left for some time.

The process of corrosion of iron is Calles rusting. The rusting of iron is a redox reaction. the black coating on silver and the green coating on copper are other examples of corrosion.

Painting, Galvanising, electroplating are some of the methods to prevent corrosion.

 

Effects of Corrosion

(i)              Corrosion causes damages to car bodies, bridges, iron railings, ships, and all objects made up of metals, specially those which are made up of iron.

(ii)           Corrosion is a wasteful process in most of cases. Every year tons of various metals especially iron get wasted in the country.

 

Rancidity

 

It is the process of slow oxidation of oil and fat present in the food material resulting in the change of smell and taste in them. The method to prevent rancidity are :

(i)              Keeping food material in air tight containers.

(ii)           Refrigeration of cooked food at low temperature.

(iii)        Packing of food items like potato wafers etc in packets containing nitrogen gas instead of air.

(iv)         Avoid keeping cooked food and food materials in  direct sunlight.

 

Part 1        Part 2

 

Chemical Reactions and Equations (Class 10 Science) Part 2

 

Balanced chemical equation

            A balanced chemical equation is that in which the total number of atoms of each element are equal on both sides of the equation. The balancing of a chemical equation is based on law of conservation of mass. According to this – “mass can neither be created nor be destroyed during a chemical reaction.”

 

            The method used for balancing chemical reaction is called hit and trial method as we make trials to balance the equation by using the smallest whole number coefficient. In this method the number of atoms of each element remains the same, before and after a chemical reaction.

 

BALANCING A CHEMICAL EQUATION

            Several steps are involved in balancing a chemical equation. These steps are as follows :-

Step (a) Writing unbalanced equation and enclosing the formulae in brackets.

(Na) + (H₂O) → (NaOH) + (H₂)

 

Step (b) Making list of number of atoms of different atoms of different elements as present in unbalanced equation.

Element	Number of Atoms in Reactants (LHS)	Number of Atoms in Products (RHS)
Na	1	1
H	2	3
O	1	1

 

Step (c) Balancing first element

            From the table shown above, it is clear that it is only the hydrogen atoms, which are unbalanced. So , firstly we try to balance it.

Atoms of H	In reactants	In products
Initialy	2 (in H2O)	3 (1 in NaOH and 2 in H2)
To Balance	2x2	2x1 in NaOH 2 in H2 = 4H atoms

Step (d) Balancing second element

            We examine the obtained equation and select another element which is still unbalanced. In the above equation, Na is still unbalanced. To balance the number of Na- atoms,

Atoms of Na	In reactants	In products
Initialy	1 in (Na)	2 (in NaOH)
To Balance	2x1	2

 

Thus after balancing Na and removing the brackets, we get the equation:

2Na + 2H₂O → 2NaOH + H₂

 

Step (e) Balancing other element

            If we further examine the reaction, no element is found to be unbalanced. This method of balancing chemical equation is called hit and trial method.

 

Step (f) Checking the correction of equation

            To check the correctness of the equation, we further tabulate the number of atoms of each element separately.

 

Element	Number of Atoms in Reactants (LHS)	Number of Atoms in Products (RHS)
Na	2	2
H	4	4
O	2	2

 

 Making a chemical equation more informative

(i)                The physical states of the reactants and products can be represented by using symbols, (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.

(ii)             The specific conditions of the reaction like temperature, pressure, catalyst etc., are written above or below the arrow in the chemical equation.

(iii)           Evolution of heat or absorption of heat can be indicated by writing [+Heat] on the right hand side or left hand side of the equation.

Example –

C_(s) + O_2(g) → CO_2(g) + Heat

Mg_(s) + H₂SO_4(aq) → MgSO_4(aq) + H₂↑

part 1       Part 3