Oxidation number of an element...

The oxidation number (o.n)  is an integer ( can be positive or negative )represented in roman numbers (for e.g :IV )  and the role of this number is to help us in balancing reactions and identifying it as an oxidation/reduction reaction.

In conventi0n , we have rules for identifying the oxidation number for elements which are :

1) The oxidation number of an element is equal to zero (O.N = 0 ) .

Examples : – Fe  O.n=0

- N₂   O.n=0

- O₂   O.n= 0

2) The oxidation number (o.n) of a mono-atomic ion is equal to the charge of the ion .

Examples : – H⁺ , O.n=+I

- N³⁻ , O.n = -III

3) The oxidation number of grouped oxygen is O.n= -II except in peroxides (H₂O₂ and N2O_{2 )} the oxidation number of oxygen becomes O.n= -I

Example : – in NaO , O.n(O)= -II

- in H₂O₂ , O.n(O) = -I

4) The oxidation number of grouped Hydrogen is O.n= +I except for hydrides ( NaH and LiH ) The oxidation number of Hydrogen is O.n=-I

Example :

- in HCl , O.n(H) = +I

- in LiH , O.n(H) = -I

5) The oxidation number of grouped elements from group 1 in the periodic table is O.n =+I  and that of group two is O.n = +II

- in NaCl , O.n(Na) = +I

- in CaO , O.n(Ca) = +II

6) In a molecule the sum of oxidation number of atoms constituting the molecule is equal to zero 

Example : NO2 , O.n(N) + 2[O.n(O)] = 0

O.n(N) -2 = 0

O.n(N) = +II

7) In a polyatomic ion the sum of oxidation number of the ions is equal to the whole charge .

Example : NH₄⁺

O.n(N) + 4[O.n(H)] = +I

O.n(N)+4(+1) = +I

O.n(N)=+I-4

O.n(N)= -III

8) The oxidation number of : – Grouped Al = +III

                                                                      – Grouped F = -I

This was a brief summary about oxidation number and the rules , if you have any questions do not hesitate in commenting or contacting me !

Chemical Change Science Projects – Cool Chem...

Chemistry science projects involving a chemical change are often chosen by middle and high school students. Many kids like to do an experiment with a dramatic chemical change. When searching for a project, it can be difficult to find an experiment with chemicals that are easy to find, and easy to work with.

One popular project involving chemicals is an experiment determining which fruit or fruit juice has the most vitamin C. A simple indicator is made with cornstarch and iodine. Students (and parents) enjoy watching the chemical reaction that occurs along with titration, which is a fancy way of saying “putting in drops”. This project can be modified in several different ways, allowing your student's creativity to shine. We get letters from many students telling us that this easy science project was submitted to the fair, and was chosen as a winner.

Another great science project involving a chemical change is watching what happens as yeast 'eats' sugar.  In this project, warm water and yeast are placed in a bottle with a bit of sugar. A balloon is placed over the mouth of the bottle. As the yeast consumes the sugar, carbon dioxide is released, causing the balloon to blow up. This project is so much fun to watch that our kids did it over and over until we ran out of yeast.

Both of these projects can be done as demonstrations; they offer dramatic reactions that students will be able to observe immediately. Both science projects can also be experiments. They naturally lend themselves to a question, the formation of an hypothesis, and testing. The results can easily be graphed to form a conclusion.

Get step by step instructions for both of these projects here. Along with a FREE Parent's Guide to Science Fair Projects, we have all sorts of ideas for your scientist, starting at the most elementary, and working up to the more advanced chemical change science projects.

Article Source: http://EzineArticles.com/?expert=Kayla_Fay
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Yield...

In the course of a chemical reaction , the experimentally obtained quantity of product is always less than calculated using stochiometric ratios .This difference is due to many factors :

a) the formation of side products other than those represented by the equation of the reaction .Thus, during the synthesis of water and oxygen , a small quantity of hydrogen peroxide also forms .

b) The loss of a portion of reactants and products during the experimental set-up of a reaction.

c) Impurities in the reactants .

The percentage yield (Y) of a reaction is the ratio of the actual yield of obtained product (experimentally determined ) divided by the theoretical  yield multiplied by 100

% yield = Actual yield over theoretical yield times 100

Significance of a chemical equation...

How do we interpret a chemical equation ?

The equation of a chemical reaction makes possible the quantitative treatment of the reactants consumed and the products formed at the microscopic scale (number of atoms , ions and molecules ) and the macroscopic scale (number of moles ) . The equation of the formation of water from hydrogen and oxygen is :

2H_2(g)+O_{2(g) –>} 2H₂O_(g)

At the microscopic scale , this equation shows that two molecules of hydrogen react with one molecule of oxygen to give two molecules of water .

At the macroscopic scale  , this equation shows that two moles of hydrogen react with one mole of oxygen to yield two moles of water .

Representation of a chemical reaction by an equati...

How do we write a chemical equation ?

A chemical reaction is represented by an equation , where the reactants and products are shown through their symbols and formulas .

The formulas or symbols of reactants are written on the left hand side of equation , and those of the products on the right hand side . They are separated bu an arrow directed from reactants to products .

The physical state of each chemical substance involved in the reaction is represented by a letter in parentheses on the right of each symbol or formula :

- (s) if it is solid

- (l) if it is liquid

- (g) if it is gas

- (aq) if it is ion in aqueous solution

Thus , the equation of the chemical reaction of iron (||) and sulfur is written as :

Fe(s) + S(s) –> FeS(s)

The equation of the reaction of iron (||) sulfide and hydrochloric acid is

2(H⁺_(aq) + Cl^-_(aq) ) + FeS_(s) –>  Fe²⁺ _(aq) + 2Cl^-_(aq) + H₂S_(g)

The substances involved in the preceding reaction form heterogeneous mixture . The corresponding reaction media is described as heterogeneous .

Conservation of mass...

In an alkaline battery , two chemical reactions take place , one at the positive terminal and the other at the negative terminal . These reactions occur continuously throughout the battery life . The mass of a new battery is equal to the mass of a used battery .

===> During a chemical reaction , the mass of products formed is equal to the mass of consumed reactants .

Reactants and Products...

During a chemical reaction there is disappearance ( consumption ) of initial substances , called reactants , and appearance ( formation ) of new substances  , called products . for example when iron and sulfur are the reactants and resulting iron (2) sulfide is the product . During the reaction , reactants are consumed and products are formed .

Application :

A + B —> AB

what are/is the reactant/s above and what are/is the product/s ?

Chemical Change of matter...

Chemical change of matter is the change in the chemical entity/state of matter ( object) , however it is totally different from the physical change where just the amount or the mass or the shape of matter changes . There are many types of chemical changes but there are 5 main types :

1- Synthesis Reaction : a synthesis reaction is when to simple elements join to form 1 more complex compound , ex:  A+B –> AB

ex (2) : H_2(g) + Cl_2(g) –> 2HCl_(g)

Hydrogen gas reacts with chlorine to reproduce Hydrogen chloride

2-Decomposition Reaction : A decomposition reaction is a reaction when a compound breaks down into two or more simpler substances .

ex: AB –> A+B

ex (2): 2H₂O_(l) –> 2H_2(g) + O_2(g)

Water decomposes into hydrogen gas and oxygen gas

3- Single Displacement : A single displacement reaction is a reaction when one element takes the place of another in a compound .

ex: A+BC –> AC+B

ex (2):Mg_(s) + 2H₂O_(l) –> Mg(OH)₂ + H_2(g)

4- Double Displacement : in a double displacement reaction ,  the positive and negative portion of two ionic compound interchange .

ex: AB+CD –> AD+BC

ex (2) : Pb(NO₃)₂ + 2Kl –> Pbl₂ + 2KNO₃

5- Combustion : a combustion reaction is a      reaction when a substance rapidly combines   with oxygen to form one or more oxides and releases energy .

ex: A + O₂ –>CO₂ + H₂O

ex (2) :C₁₀H₈ + 12 O₂ —> 10 CO₂ + 4 H₂O