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Stoichiometry - COMBINATIONS OF ELEMENTS AND THEIR REACTIONS:  Study chemical reactions by reading sections on stoichiometry in chemistry text books and demonstrating them with laboratory experiments.  (See laboratory cautions below). Combining elements to form new combinations is a very important part of chemistry. (If you don't know the meaning of the words here look them up in the "TERMS" links provided below.  Also look up the words in your dictionary for additional understanding.)  Learn about the concept of a MOLE.  Learn more about chemical reactions HERE.

In a simple equation, such as the synthesis of iron(II) sulfide,
iron + sulfur = iron(II) sulfide the equation requires no special balancing:

Fe + S  Ž   FeS

Our last stage is to put in state symbols, (s, l, g, aq), as appropriate.

Fe(s) + S(s)  Ž   FeS(s)

On a molar basis, we can say that one mole of iron (56g) reacts with one mole of sulfur (32g) to produce one mole of the compound iron(II) sulfide (88g).

You will need the ability in chemistry to describe formulas for any substance you come across.  For ionic compounds the compound formula may be arrived at by knowing the number of charges each ion has.  Memorize this table.  For example sodium (Na) has a charge of +1.  Oxygen (O) has a charge of -2.  Carbon (C) has a charge of -4.  When you see these elements in a formula; substitute the charge numbers and that will tell you how many atoms of each element are needed to balance the equation.

For example if you combine sodium (Na) and chlorine (Cl) that is the same as +1 = -1 = 0 so you only need one of each.  When we say one, it could mean one atom or one mole.  So the formula for  a combination of sodium and chlorine is Na+Cl- or often written with out the superscripts as NaCl.   This is sodium chloride or common table salt.  What about aluminum and chlorine?  +3 = -1 = +2  In this case you need two chlorine (whatever) to balance the equation for the compound.  It would end up as Al3+ 3 Cl- which is AlCl3.  Some elements can have various charges like iron.  They are written with roman numerals to indicate the charge; iron(II) Fe2+, iron(III) Fe3+, etc.

Reactions http://web.jjay.cuny.edu/~acarpi/NSC/6-react.htm
Graphics http://ull.chemistry.uakron.edu/genobc/Chapter_05/
Key Points http://www.chem4kids.com/files/react_intro.html
Predicting reactions http://www.spusd.k12.ca.us/chemmybear/preactions.html
Chemical Reactions
http://www.visionlearning.com/library/module_viewer.php?mid=54
Chemistry Experiments you can do at home - http://www.bxscience.edu/~chinyu/2690/exper/exper.htm
Lab Books Online - Phoenix College  http://chemlab.pc.maricopa.edu/labbooks/default.html
Lucid stoichiometry (LSU)
Hints for solving stoichiometry problems (Widener U)
Stoichiometry: mass-mass problems (ChemCentral)
Stoichiometry worksheet (Georgetown College)
Stoichiometry introduction (limiting reagent) (Carnegie Mellon)
Stoichiometry (limiting reagent simulation)
Stoichiometry 1 (Wilton High School)
Stoichiometry 2
(Wilton High School)
Stoichiometry 3 (Wilton High School)
Stoichiometry 4 (Wilton High School)
Stoichiometry (DBHS)
Stoichiometry by the recipe (John Brodemus)
Stoichiometry applet (IrYdium Project)*
Stoichiometry notes (Erik)
What is stoichiometry (Floyd College)
Chemical reaction stoichiometry web site (Smith)
Mass relationships in chemical equations (CSU-DH)
Stoichiometry online (GSU)

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Polyatomic

 Polyatomic Ions Formula Name Formula Name C2H3O2- acetate ion NO3- nitrate ion NH4+ ammonium ion Cl4- perchlorate ion CO32- carbonate ion PO43- phosphate ion CN- cyanide ion SiO44- silicate ion HCO3- bicarbonate ion SO42- sulfate ion OH- hydroxide ion SO32- sulfite ion
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Some Common Polyatomic Ions

 Ammonium NH4+ Chlorate ClO3- Peroxide O2-2 Acetate CH3COO- Perchlorate ClO4- Chromate CrO4-2 Nitrate NO3- Permanganate MnO4- Dichromate Cr2O7-2 Nitrite NO2- Carbonate CO3-2 Silicate SiO3-2 Hydroxide OH- Sulfate SO4-2 Phosphate PO4-3 Hypochlorite ClO- Sulfite SO3-2 Arsenate AsO4-3 Chlorite ClO2- Thiosulfate S2O3-2 Arsenite AsO3-3 Cyanate CN- Thiocyanate SCN- Borate BO3-3 Bicarbonate HCO3- Bisulfate HSO4- Bisulfite HSO3-

Now that we know something about the make up of compounds lets look at a reaction formula.  Suppose you add sulfuric acid to sodium bicarbonate and obtain as products carbon dioxide gas, sodium sulfate, and water.

NaHCO3  +  H2SO4    Ž      CO2    +    Na2SO4    +    H2O

Notice in order to form a molecule of sodium sulfate you must put in two sodium atoms.  To get two sodium atoms you need two molecules of sodium bicarbonate.  Therefore, the "balanced" equation becomes:

2 NaHCO3    +    H2SO4    Ž      2 CO2    +    Na2SO4    +    2 H2O

 Greek Prefixes Prefix Number Prefix Number mono- one hexa- six di- two hepta- seven tri- three octa- eight tetra- four nona- nine penta- five deca- ten

REACTION STOICHIOMETRY

1.  Write the unbalanced equation.

H2SO4    +   Al    Ž      Al2(SO4)3  +  H2

2.  Balance the equation.

3H2SO4  +   2Al   Ž      Al2(SO4)3  +  3H2

3. Convert the known masses of the molecules to moles using molecular weight form the periodic table.

H2SO4:  5x10-1 / 98.079 (g/mol) = 5 x 10-3 moles

4.  Use the balanced equation to set up mole ratios.

3 mol (H2SO4):   2 mol (Al):   1 mol (Al2(SO4)3):   3 mol (H2)

5.  Use the mole ratios to calculate the number of moles of the desired reactant or product.  If the mass or the mole of only one species in the equation is known, use it to calculate the rest according to the coefficient (mole ratios) of the equation.  Otherwise, find the limiting reagent and use it to calculate the rest.  Since only the moles of H2SO4 is known we multiply it by the corresponding ratio to obtain the moles for other species.

H2SO4:        5 x 10-3 moles

Al:                 3 x 10-3  moles

Al2(SO4)3:    2 x 10-3   moles

H2:                 5 x 10-3  moles

6.  Convert from moles back to grams using molecular weights.

H2SO4:        5 x 10-3 moles x 98.07 (g/mol)        =  5 x 10-1 g

Al:                 3 x 10-3 moles x 26.98154 (g/mol)  = 9 x 10-2 g

Al2(SO4)3:    2 x 10-3 moles x 342.154 (g.mol)    =  6 x 10-1 g

H2:                 5 x 10-3 moles x 2.01588 (g/mol)    = 1 x 10-2 g

Famous scientist quote:
"In many carefully made experiments, Volta has observed that two metals put in contact become electric, and that this is the cause of the phenomena of the electric pile.  Davy later showed that this electrical state increases due to force of mutual affinities of the bodies used, and that this effect can be produced, and even seen, by means of certain precautions, in all bodies which have affinity for each other."  Jons Jakob Berzelius (1779 - 1848)