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Sunday, April 13, 2014

Problem Solving Assessment (PSA) result 2014

The second Problem Solving Assessment (PSA) for Academic Session 2013-14 was conducted on 19-10-2013 for Winter Bounds Schools and on 18-01-2014 for Summer Bounds Schools for Classes IX and Class XI. This also included (optional) improvement in PSA by students currently in Class X/XII.
The Board has declared the results of second Problem Solving Assessment (PSA) for Academic Session 2013-14 and the results have been sent to all schools through e-mail.
Note:
  • Those who have not received the results may obtain the same by sending email to : bmgupta.cbse[at]nic.in  by giving 5 digit school code
  • Last date for Uploading of assessment data for Class IX Term-II and Class X Term II is 15th April, 2014.

Basic Science Class 8

We are providing you scanned copy of exercise so that you can check your study chapters are:
1. Food production
2.The cell
3. Micro organism
4. Reproduction
5. Synthetic Material
6. Metal and non metals
7.Combustion and Flame
8.Force and Pressure

Class VIII Mathematics [Click on links given below]
CBSE Class VIII Science

Friday, April 11, 2014

CBSE Class 10 Sample Paper SA-1 Sep 2014

Oxidation and Reduction on the basis of electrons transfer

Oxidation and reduction reactions










These are reactions where electrons are transferred from one species (atom, molecule or ion) to another. We can write 'half' equations to show only what happens to the species losing electrons or a different 'half' equation to show the species gaining electrons.

The whole equation is put together by making sure that the numbers of electrons are balanced in each half equation and adding them together (when the electrons will cancel out)

Oxidation is a chemical process in which there is a loss of electrons. The species, which gets oxidized becomes more positive or less negative, e.g.,
Na  Na+ + e- (Na is oxidized to Na+ )
Fe2+ 
 Fe3+ + e- (Fe2+ is oxidized to Fe3+)
Reduction is a chemical process in which there is a gain of electrons. The species, which gets reduced becomes more negative or less positive, e.g.,
Cl2 + 2e-  2Cl- (Cl2 is reduced to Cl-)
S + 2e- 
 S2- (S is reduced to S2- )
The Oxidizing agent is the species which accepts electrons, e.g.,
Sn4+ + 2e-  Sn2+ (Sn4+ is an oxidizing agent)
F2 + 2e- 
 2F- (F2 is an oxidizing agent)
The Reducing agent is the substance which loses electrons, e.g.,
Hg+  Hg2+ + e- (Hg+ is a reducing agent)
Fe2+ 
 Fe3+ + e- (Fe2+ is a reducing agent)
Examples

2FeCl2 + Cl2 2FeCl3
The iron changes from 2+ to 3+ and is therefore oxidised (removal of electrons)
The chlorine gains an electron to go from 0 to -1 and is therefore reduced (addition of electrons)

Zn + CuSO4  Cu + ZnSO4
The zinc changes from oxidation state 0 to +2 (removal of electrons) it is oxidised (animation)
The copper changes from 2+ to 0 and is oxidised and is therefore reduced (addition of electrons)

Cr2O72- + 3SO2 + 2H+ 2Cr3+ + 3SO42- + H2O
The chromium changes from +6 to +3 and is therefore reduced (gain of electrons)
The sulphur changes from +4 to +6 and therefore loses electrons = oxidation (loss of electrons)

2KI + Br2   2KBr + I2
The iodide ions (oxidation number = -1) change to iodine (oxidation number = 0) : oxidation
Bromine (element, oxidation number = 0) changes to bromide ions (oxidation number = -1) : reduction

5Fe2+ + MnO4- + 8H+  5Fe3+ + Mn2+ + 4H2O
The iron changes from 2+ to 3+ and is oxidised (removal of electrons)

The manganese atom changes from +7 to +2 and is therefore reduced (addition of electrons)

More post describing redox reaction

The Effects of Oxidation Reactions : Many metals are chemically active elements and get easily affected by substances like moisture, air, acids, etc. Example-Iron articles that are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Rusting eventually causes structural weakness and disintegration of the metal.
When a metal is attacked by substances around it, it is said to corrode and this process is called corrosion. Corrosion causes deterioration of essential properties in a material..............Read more

In our daily life we come across phenomena like fading of the colours of the clothes, burning of combustible substances like cooking gas, wood and coal, .................................... Read more  
science class 10 oxidation, reduction and redox chemical reaction

Chemistry x - OXIDATION AND REDUCTION : Oxidation: A chemical reaction which involves addition of oxygen or removal of hydrogen or loss of electron(s) is called as oxidation.
2Mg + O2 →2MgO (addition of oxygen)
H2S + Br2 → 2HBr + S (removal of hydrogen)
Fe2+ → Fe3+ + e- (loss of electron)           ..........................................................,,,,,,,,,Read more