Tutorial with feedback  -  (130)Balancing chemical equations  

Types of Reactions:

There are a few basic types of chemical reactions, these can be broken down into three types:  double substitution or replacement, reduction – oxidation, and polymerization reactions.  Within the reduction - oxidation reactions, the basic types of reactions include single replacement, decomposition, combination or synthesis and combustion reactions.  Polymerization reactions are similar to combination or synthesis reactions.

To predict the products of a reaction, you must be able to identify the type of reaction.  

• A double replacement reaction always involves the reaction of two ionic compounds (binary ionic, ternary ionic, binary acid, ternary acid, ammonium salts, or bases), 

• a single replacement reaction always involves the reaction of one ionic compound with an element, 

• the decomposition reaction always begins with one reactant which can be either an ionic or a covalent compound, while

• the combustion reaction involves a covalent compound which contains Carbons and Hydrogens (a hydrocarbon) in the presence of oxygen, O2, will always produce CO2 and Water.  

• The hardest reaction to predict is the combination reaction.  The easiest way to determine this reaction, is by elimination of all the other types of reactions.

The first basic type of reaction that occurs is called reduction – oxidation (REDOX) reactions.  These reactions involve the transfer of electrons from one species to another.  To understand redox reactions, one must understand the charge or oxidation state of atoms in compounds.  Redox reactions can be separated into several types which include: 

• Synthesis and Decomposition reactions are often the most difficult to predict the products without a greater knowledge of basic chemistry.   Synthesis or combination reactions are simply as the name implies, putting all the reactants together into one product, while a decomposition reaction breaks one reactant into many products. 

Combination or Synthesis reactions, in general, can be represent as several reactants making one product

 Mg       +            N2            →             Mg3N2                          Combination

While decomposition reactions, can be represented as one reactant making several products. 

 PbO2     →        PbO  +              O2           Decomposition 

• The single replacement reaction involves the transfer of chemical or ionic partners.  The following is an example:   Al  + CuSO4 →  Al2(SO4)3  + Cu.  When writing the products of the reaction the charges on the individual ions must be taken into account.  What is the charge or oxidation state on the sulfate ion? What is the charge on the copper ion? What is the charge on Aluminum on the reactant side? What is the charge on the aluminum ion on the product side? Which ion is bonded to aluminum on the product side?

  • • What happened to the charge on Aluminum?   Al is neutral and it changes to have a +3 charge on the product side, aluminum has lost 3 electrons.  This is written as a half reaction Al →   Al+3   +   3 e-1.  This half reaction, the loss of electrons is called an oxidation half reaction.  

    • The gaining of electrons  Cu2+ + 2 e-1 →  Cu is the reduction half reaction. 

• A combustion reaction always contains a hydrocarbon which is a substance that contains both carbon and hydrogen, reacting with oxygen.   Most hydrocarbons are a good fuel, so they burn readily.  The combustion reaction represent the complete combustion of the hydrocarbon to carbon dioxide and water.   
  An example of a hydrocarbon burning in the presence of oxygen gas is   2 C3H7CHO   + 11 O2  →  8 CO2 +  8 H2O  

The second type of reaction and the most common in the first semester laboratory is a double replacement or metathesis reaction.  

• double substitution or replacement reactions require a rearrangement of the chemical bonds between two ionic compounds.  This is not a REDOX reaction generally because the reaction involves simply switching ionic partners and the ions involve do not change.  So it is fairly easy to predict the products of this type of reaction if you understand the ions present in an ionic compound. 
  Generally it is written as AB + CD →  AD + CB, where A and C are cations and B and D are anions.   What has occurred to the bonding partners?

              This is a real example:                       Zn(OH)2  +     H2SO4     →    ZnSO4 +    H2O

• • • Zinc, the positive ion, is with the hydroxide ion, the anion, while hydrogen, the cation,  is with the sulfate ion, the negative ion,  on the reactant side of the reaction.  What is zinc with on the product side of the reaction?   Notice that the zinc changes bonding partner with the hydrogen.  Notice also that the positive ions do not bond together but we maintain a cation bonded to an anion. 

    • Why is zinc with two hydroxide ions but only one sulfate ion?  The charges on the ions must be balanced.  The total positive charge must be equal to the total negative charge so that the resulting compound remains neutral.  

Predicting Products of the Reaction:

• To predict the products of a double replacement reaction.  When the products are predicted, their charges balanced, then the overall reaction is balanced to maintain the correct number of atoms on both sides of the reaction.  To balance and predict the products of the following reaction, many items must be considered.   

                              CuCl2  +   Na2CO3  →

• • When writing the products of the above reaction the charges on the individual ions must be taken into account.  You can use the  Appendix G:  Periodic table of common oxidation states to determine the charges of monatomic ions.  Appendix H:  Common and Polyatomic ions can be used to recognize the many different polyatomic ions; however, a few of these must be memorized.  

    • What is the charge or oxidation state on the chloride ion? Chlorine is a non metal that generally has a -1 charge.

    • What is the charge on the copper ion?  Copper is a transition metal that can have more than one oxidation state, either +1 or +2.  To determine the charge that copper carries in CuCl2we can look at the total charges on the chloride ions.  Since each chloride has a -1 charge and there are two chloride ions, the total negative charge is -2; therefore, the copper much carry a +2 charge to balance the negative charge on the chloride ions.   

    • What is the charge on the sodium ion?  Sodium always carries a +1 charge.  

    • What is the charge on the carbonate ion?  The carbonate ion is a polyatomic ion, CO32-,  this ion as a total carries a -2 charge.

    • Which ion will bond to Copper on the product side?  Copper is a cation; therefore, it will change places with the sodium ion, which means the copper will bond with the carbonate ion.  Given the charges on copper and its new partner, what is the chemical formula of the product?  Since Cu2+  is bonded with CO32- , the charges are equal and opposite, the formula is CuCO3. 

    • Which ion will bond with sodium?  Given the charges on sodium and its new partner, what is the chemical formula of the product?    Na+ will bond with Cl1- since these are also equal and opposite charges, the chemical formula will be NaCl

• Double replacement reactions can generally be characterized as either acid – base reactions or precipitation reactions.  An Acid – Base or neutralization reactions occurs when an acid, which contains a hydrogen atom that can ionize in water to H+ ion, reacts with a base, which either contains OH-1 (hydroxide ion) or accepts the H+ ion from the acid.  For example:  HCl + NaOH ®  NaCl + HOH.  HCl is an acid because it has hydrogen written in the first position.  This does not always indicate an acid, but almost all acid have hydrogen written first.   NaOH is a base because it contains the hydroxide ion.

  • A precipitate is the formation of an insoluble solid when two solutions are mixed.  Solubility is very important in understanding whether the reaction will occur. Some substances are soluble in water and others are not.  The solubility of ionic compounds can be predicted by the ions present.  Look up solubility rules in the Appendix of the Lab Manual. 

• When two separate aqueous ionic compounds are mixed the ions may interact.  The ionic compounds in a double replacement reaction switches partners.  If these partners result in a compound that remains dissolved, then the products of the mixture are strong electrolytes and the reaction is said to have no apparent reaction.  When the product of the double replacement reaction is a precipitate or solid, a weak electrolyte or acid, a non electrolyte or a gaseous substance, the removal of the freely dissociated ions results in the removal of ions from solution and a chemical change has occurred. 

• The driving forces that cause a reaction to occur are

  • • the formation of a solid or precipitate which results from the formation of a substance that has limited or no solubility.

      • The solubility rules are used to predict which substances will be more likely to form a precipitate.

    • the formation of a gas which is most commonly seen when the reaction results in the formation of two common weak acids:  carbonic acid: H2CO3 which dissociates to make water and CO2 gas and sulfurous acid, H2SO3, which dissociated to make water and SO2 gas; and

    • the formation of a weak or non electrolyte, such as water, which is generally recognized by the evolution of heat or

    • a significant change in temperature.

Procedure and Report 

The Laboratory Report of the assignment contains questions, data collection, calculation and reporting of results.   Use the simulations or class data to complete this assignment.

  Reaction 3:   Reaction of Hydrogen peroxide, H2O2 with MnO2:   

  Reaction 4:   reaction of calcium acetate and ethanol

Part B - Single Replacement Reactions

  Reaction 1:   copper sulfate and zinc metal

  Reaction 2:    zinc metal and hydrochloric acid

   Reaction 3:   Calcium metal with water

 Additional Reactions:

• • • 10 reactions:   https://youtu.be/QH91PHkuy48 

    • Heating of sucrose or sugar:  http://youtu.be/HUDeUYR7iUs

    • Lithium metal in water  - http://www.periodicvideos.com/videos/003.htm ; http://youtu.be/Vxqe_ZOwsHs;  

    • Sodium metal in water - http://www.periodicvideos.com/videos/011.htm ; http://youtu.be/pizqEbbDE_A ;http://youtu.be/ODf_sPexS2Q 

    • Potassium metal in water - http://www.periodicvideos.com/videos/019.htm ; 

    • Rubidium metal in water - http://www.periodicvideos.com/videos/037.htm 

    • Cesium metal in water - http://www.periodicvideos.com/videos/055.htm ;

    • Rubidium with water:  http://youtu.be/a5EBrTRgZfM 

    • Cesium with water:  http://youtu.be/PKHXtSb6O7c    http://youtu.be/jJGqC4vXBms 

    • Francium - http://www.periodicvideos.com/videos/055.htm

Part C - Double Replacement Reactions

  Reaction 1:   Hydrochloric acid with sodium carbonate:  

• • similar with sodium bicarbonate:  http://youtu.be/xRfPvDEs2gM

Clips of reactions:

Giant Gummy Bear Fireball:   https://youtu.be/JOHdZsQXw7I 

Videos about the elements on the periodic table:   http://www.periodicvideos.com/

The visual periodic table:   http://periodictable.com/

The Pharaoh Snake Experiment    http://youtu.be/NNHTz1j48qc

Joe's Cafe - A lot of interesting reactions:   http://youtu.be/8TPnns-5UxA

Sugar Explosion:   http://youtu.be/Jg7mLSG-Yws

Bill Nye:  http://youtu.be/66kuhJkQCVM

Periodic Table Reactions:  http://youtu.be/UkBhW8Kj3r8

Copper with Nitric Acid:  http://youtu.be/pJSQq494oV4

Magnesium in Dry Ice:   http://youtu.be/_xCbal2YyaE

Silver Mirror reactions:  http://youtu.be/y-4qqcCxD6g

Copper to Silver to Gold:  http://youtu.be/eVdPxuUvIII

Reaction of the halogens with iron:  http://youtu.be/EvtyMr5EvBY

Methane combustion:  http://youtu.be/xDlGSkTbh2A

The Fountain Reactions:   http://youtu.be/X1BktOPsc7g