UNIT 3.Notes- chemical reactions by xuyuzhu

VIEWS: 5 PAGES: 8

									                                         UNIT 3: Chemical Reactions


1. Symbols in chemical reactions
Section 10.2 page 398 and 10.5 pages 406-407

A chemical reaction is denoted by an arrow pointing from the starting materials (the
reactants) to the new substances (the products).

H2O2  H2O + O2

In the reaction above, what are the reactants? ____________
What are the products? ____________

It is also useful to know the physical state of the substances involved in the chemical
reaction. The symbols used to specify the chemical state are listed below.
Solid ________ liquid _______ gaseous _________ aqueous _________

The term aqueous means “dissolved in water”. Many substances such as solid ionic
compounds cannot react until they are dissolved in water.

You may also see coefficients in front of the reactants and products of a chemical
reaction. These indicate the ratio in which the reactants make the products. You will
learn how to find these ratios at the end of this unit.

2.Types of Reactions
Section 10.6 pages 407-410


Explain the following type of chemical reactions & give
examples-

     Synthesis:




     Decomposition:




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     Single Replacement:




     Double Replacement:




     Combustion:




Predict the products (when not already given) and identify
the type of reaction


1)      Na3PO4 + 3 KOH       _________________________


3)      C6H12 + 9 O2         _________________________


4)      Pb + FeSO4          _________________________


5)      CaCO3  CaO + CO2     _________________________


6)      P4 + 3O2  2 P2O3     _________________________


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3. Conservation of Mass
Section 10.1 pages 396-398

In a chemical reaction, the mass of the combined reactants is always equal to the mass of
the combined _______________.

When you decompose 38 grams of hydrogen peroxide, you make
18 grams of water. What is the mass of the oxygen gas that
is produced?

Conservation of Mass Lab
    *During the lab you will also learn how to calculate % Yield and % Error


4. Balancing equations
Section 10.3-10.4 pages 399 -407

Since there must be an equal number of atoms entering a reaction as coming out as
products, we “balance” equations. This process involves adding coefficients in front of
reactants and products. As you will learn later, these coefficients indicate the ratio of the
substances involved in the chemical reaction.

The coefficient multiplies the entire molecule or in the case of ionic compounds, formula
unit. For example, 2H2O means there are 2 water molecules which means there are 2
hydrogen and 4 oxygen. To find out how many of each atom there are, multiply the
coefficient by the subscript.

How many oxygen atoms are part of the following chemical
formulas?
a. 3SO2 b. 6H2SO4 c. 5Al2(CO3)3

We will balance the following equations in class together.

Simple:

__ C + __ H2  __ C3H8



Double replacement:
*Balance polyatomic ions as a unit (don’t break into elements)

__ NaI + __ Pb(SO4)2  __ PbI4 + __ Na2SO4


When elements appear in multiple different reactants or products:


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*Balance those elements last (oxygen in this case)

__ Fe2O3 + __ H2O  __ Fe(OH)3


When there are fractional coefficients
*Many time combustion reactions will behave this way

__ C6H6 + __ O2  __ H2O + __ CO2




5. Acids and Bases

Acids and bases are very common and important substances. They are involved in both
biological and industrial applications. Acid base chemistry has many levels of depth and
complexity but we will focus on the basics.

How to recognize an acid:
A compound that begins with hydrogen (H). Examples – H2SO4, HCl

How to recognize a base:
A compound with the hydroxide ion*. Examples – NaOH, Ca(OH)2
*There are many other bases but these are the ones you need to recognize for this class*




Properties of acids:
    Taste sour
    Turn litmus paper red
    React with metals to liberate hydrogen gas
    Acids are molecular compounds when not in solution but when placed in
       solution they “ionize” (produce ions). Acids the ionize completely are
       considered strong acis and those that ionize only partially are weak acids.

Properties of bases:
    Taste bitter
    Turn litmus paper blue
    Feel slippery
    Bases containing the hydroxide ion are ionic. When ionic compounds
       dissolve in solution they “dissociate”.

The pH scale:


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On the pH scale, a low pH (below 7) means the solution is ________________ and a
high pH (above 7) means the solution is ________________. A pH of 7 is considered
neutral.


Acid – Base reactions:
Acids and bases react to produce a salt and water.
Example:
HCl + NaOH  NaCl + H2O

What other category of reaction could the above example
belong to?



Demo: Which compounds cause the light bulb to light?

Ionic:
Strong Acid:
Weak Acid:
Molecular (not acidic):


What is the difference between a strong and weak acid?




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                         Review Questions

  1. Is volume conserved in a chemical reaction? What
     about mass? How is it possible for one to be
     conserved and not the other?




  2. What are the products of a combustion reaction
     involving a hydrocarbon as a reactant?
  3. What type of reaction are the following?

        a. C5H5 + Fe  Fe(C5H5)2

        b. SeCl6 + O2  SeO2 + 3Cl2



Predict the products and tell which type of reaction is
occurring in problems 4-10

  4. MgCl2 + Li2CO3 

  5. RbNO3 + BeF2 

  6. AgNO3 + Cu 

  7. C3H6O + 4 O2 

  8. MgI2 + Mn(SO3)2 

  9. Li + O2   

  10.     NO2 


Balance the equations in problems 11 - 21

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11.     __ NH3 + __ O2 __ NO + __ H2O


12.     __ Fe(OH)3  __ Fe2O3 + __ H2O


13.     __ HNO3 + __ Mg(OH)2  __H2O + __ Mg(NO3)2


14.     __ H3PO4 + __ NaBr  __ HBr + __ Na3PO4


15.     __ CaO + __ MnI4  __ MnO2 + __ CaI2


16.     __ Fe2O3 + __ H2O  __ Fe(OH)3


17.     __ C2H2 + __ H2  __ C2H6


18.     __ VF5 + __ HI  __ V2I10 + __ HF


19.     __ OsO4 + __ PtCl4  __ PtO2 + __ OsCl8


20.     __ CF4 + __ Br2  __ CBr4 + __ F2


21.     __ Hg2I2 + __ O2  __ Hg2O + __ I2


22.     What is the difference between ionization and
  dissociation?


23.     If you have 23 grams of reactant and 21 grams of
  product


      a. What is your percent yield?



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      b. What is your percent error?


24.      If you the mass of your product was greater than
  that of your reactant during the lab, give two sources
  of error to explain this phenomenon.




25.     What would two sources of error be if your
  product was less than reactant?




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