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Chemical Formulas                                                              Experiment 7


1.0 Introduction

   When ionic compounds are formed the ions must always balance so that positive and
negative charges are equal. Sometimes this involves using two or more of one ion to balance
the other. The patterns of ionic compounds (salts) are shown below. Hint: Notice that each
charge can be used as the number of the “other” ion (like cross multiplication) but when
they are equal they cancel to 1.

Cation (example)             Anion (example)              Resulting Compound (example)

  M+ ( Na+ )                    X-    ( Cl- )                   MX             ( NaCl )

  M2+ (Ca2+ )                   X-    ( Cl- )                   MX2            ( CaCl2 )

  M3+ ( Al3+ )                  X-    ( Cl- )                   MX3            ( AlCl3 )

  M+ ( Na+ )                    X2- ( O2- )                     M2X            ( Na2O )

  M+ ( Na+ )                    X3- ( N3- )                     M3X            ( Na3N )

  M2+ ( Mg2+ )                  X2-   ( O2- )                   MX             ( MgO )

  M3+ ( Al3+ )                  X3- ( N3- )                     MX             ( AlN )

  M2+ ( Mg2+ )                  X3- ( N3- )                     M3X2           ( Mg3N2 )

  M3+ ( Al3+ )                  X2-    ( O2- )                  M2X3           ( Al2O3 )

  Charges for many ions can be found from looking at the group numbers on the periodic
table. Some ions including many transition metal ions have two (or even more) charges and
these must be memorized. Also, there are many polyatomic ions that are important and
must be memorized. When polyatomic ions are used in formulas they must be placed in
parentheses when more than one is needed. For example Al(NO3)3 , (NH4)2SO4 , Al2(CO3)3
or Ca(OH)2

Important polyatomic ions (Useful in biochem, health and nutritional sciences)

SO42- sulfate (xray tech, nutrition)                NH4+ ammonium (common buffer cation)

NO3- nitrate     (fertilizer, many soluble salts)   C2H3O2- acetate (common in buffers)

PO43- phosphate (fertilizer, biomolecules)          also “H” containing ions HCO3- etc.

OH- hydroxide (common base ion )

H3O+ hydronium (acid proton in water)

CO32- carbonate (common ion in blood)

                                                                  College of San Mateo Chemistry Dept
34
Chemical Formulas                                                          Experiment 7


2.0 Chemical Formula Exercise

  For each of the following compounds give a formula. Notice where each of these
compounds is found or how they are used.


Acids                                    Use                               Formula

hydrochloric acid           stomach acid, used in pools (Muriatic acid)    ________________


sulfuric acid               auto batteries, used for manufacturing         ________________
(formed from sulfate ion)

acetic acid               vinegar                                          ________________
(formed from acetate ion)

carbonic acid             carbonated drinks                                ________________
(formed from carbonate ion)

boric acid                  diluted for eye wash                           ________________
(get help for this one)


hydrogen sulfide (gas)      rotten egg smell                               ________________


Bases

sodium hydroxide            lye, drain cleaner, make soap                  ________________


magnesium hydroxide         milk of magnesium antacid                      ________________


ammonia                     glass cleaner, smelling salts                  ________________


calcium hydroxide           lime water test for CO2                        ________________




                                                              College of San Mateo Chemistry Dept
                                                                                              35
Chemical Formulas                                                          Experiment 7


Salts                                    Use                               Formula


calcium carbonate         limestone, chalk and Tums antacid                ________________


sodium chloride           salt, saline solution for blood hydration        ________________


sodium fluoride           fluoride in toothpaste                           ________________


selenium sulfide          antidandruff compound Selsun Blue                ________________


sodium phosphate          “triphos” soaps                                  ________________


barium sulfate            Insoluble coating for xrays in colon etc         ________________


iron(II) sulfate           used as nutritional iron supplement             ________________
(numeral gives the charge)

magnesium oxide           used as nutritional magnesium supplement         ________________


ammonium phosphate        used in fertilizers                              ________________


potassium oxide           “potash” often used in fertilizer                ________________


potassium nitrate         salt peter used in fertilizers, gunpowder        ________________


copper(II) sulfate        used to prevent algae growth                     ________________


magnesium chloride        common salt found in “sea salt”                  ________________


potassium chloride        salt substitute for high blood press.            ________________


zinc oxide                medical antiseptic and astringent                ________________




                                                              College of San Mateo Chemistry Dept
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                              College of San Mateo Chemistry Dept

								
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