Make your own free website on Tripod.com

The Mole

The MOLE ... and other Chemical Quantities



I. Quantitative Use of Chemical Formulas

A. Counting Atoms


H2O             contains                    ___ _________ of H
                                                    ___ _________ of O



K2Cr2O7        contains                    ___    atoms   of    K
                                                     ___    atoms   of    Cr
                                                     ___    atoms   of    O



Ca(OH)2       contains               ___     atoms  of  Ca

                                                ____   atoms  of   O
                                                ____   atoms  of   H


CuSO4 . 5 H2O contains            ____ atoms of Cu
                                                 ____ atoms of S
                                                 ____ atoms of H
                                                 ____ atoms of O



B. Calculating the Formula Weight

________________ ______________   of a substance = the weight in amu of all the atoms in a given formula



To calculate the FW (formula weight) of H2O

2 atoms H = 2 (                        ) =
1 atom  O = 1 (                        ) =  ________________

                                           FW = 



Find the FW of K2Cr2O7

2 atoms K = 2 (                        ) = 
2 atoms Cr = 2 (                       ) =
7 atoms O = 7 (                         ) = _____________

                                             FW = 



Find the FW of Ca(OH)2

1 atom Ca = 1 (                         ) =
2 atoms O = 2 (                         ) = 
2 atoms H = 2 (                         ) =  _______________

                                             FW = 


Find the FW of 

a) N2O4                                       e) C12H22O11

b) MgBr2                                                  f) Fe2(Cr2O7)3

c) HNO3 (aq)                                g) CuSO4 . 5 H2O

d) Ca3(PO4)2                                         h) KCl 


C. Using the Formula to find PERCENT COMPOSITION

______________________ - relative amounts of each element in a compound

To compute percent composition:

1) Find the FW (formula weight) of the compound

ex. H2O

H = 2 ( 1.01 amu )    =    2.02 amu
O = 1 ( 16.00 amu )  =  16.00 amu
                          FW =  18.02 amu

2) Find the _____________________ of each element by: _______________________________________________________________

_______________________________________________________________

_______________________________________________________________


% H  =  ______   X   100 =                 %

% O  =  ______   X   100 =                 %


3) Compute all percents to one decimal place then check to see if they total 100


D. Using the PERCENT COMPOSITION

Suppose you have a pile of __________ C6H12O6 with a mass of 28 g
What is the mass of C that is in that pile?

1) Find the FW of C6H12O6

C =         (                    ) =
H =         (                    ) = 
O =         (                    ) = ______________


2) Find the percent of C in C6H12O6

%       =       _______ ______   x     100 = 


the percent is a ______________:  



3) Use this conversion factor to solve the problem:

28   g    C6H12O6 

Example: What mass of glucose C6H12O6 will contain 50 g of Carbon?

1) Find the FW of glucose



2) Find the % composition of Carbon


3) Use the conversion factor, but make sure the units cancel !!

 

 

 

 

 

 


II. The MOLE

A. Defining the MOLE

1. IUPAC definition

The International Union of Pure and Applied Chemistry (IUPAC) defines the “mole”:

The mole is the amount of substance of a system which contains as many elementary particles 

as there atoms in 0.012 kilogram (or 12 grams) of carbon-12. 

In other words: in one _________ of carbon - 12, , there are __________________ carbon - 12 atoms

One mole of ANYTHING contains 6.02 x 1023 representative particles

In chemical terms:

______________________ = the smallest unit into which a substance can be broken down without a change in composition; the term refers to whether a substance commonly exists as atoms, ions, molecules

If the substance is an _______________________ (but, not a diatomic element), RP = _________________

If the substance is a _______________________________, RP =________________________

If the substance is an ______________________________, RP = ________________________

Examples:                       Substance                              Representative particle

                                      water

                                      magnesium

                                      salt



2. Avogadro’s Experiment (1811)

By experimenting with gases, a scientist named ____________________ determined the ____________________ present in a given amount of an element:





1.01  gram sample of H                                      16.00 gram sample of O

Avogadro determined that there were _______________ atoms in each sample!

__________________________________________________________

Conclusion of Avogadro's experiments:
Whenever you mass out the __________________ of an element, you will have ________________ atoms in the sample. This number is called _________________________


C. The MOLAR MASS

1.  Atoms



63.55 g Cu                                                          32.06 g S 


Each sample contains _____________________ atoms: this is called a ____________ of atoms

The ________________ ____________ of any element is the mass in grams of 1 mole of that element

            Units:

 

What is the molar mass of the following elements?

a)  copper                                                 d) sodium

b)  sulfur                                                   e) carbon

c)  magnesium

2. Molecules

 





18.02  g  H2O                                                342.22  g  C12H22O11

Each sample contains  __________________________: this is a ______________ of molecules

The _______________ _______________ of a molecular compound is the _______________

Units:

 

What is the molar mass of the following molecular compounds?

a) NH3

b) CO2

c) Cl2

d) C6H12O6

3.  Formula Units





58.44  g  NaCl

This sample contains  _______________________: this is a ____________ of formula units

The __________________ ________________ of an ionic compound is the ____________________

Units:

What is the molar mass of the following ionic compounds?

a) MgO

b) CaCl2

c)  Mg(OH)2

d) Al(NO3)3

. The _________________ of a substance is the mass in grams of one mole

. One mole contains 6.02 x 1023 representative particles

. The ____________ of a substance is the ________________ in 

What is the representative particle in a:

a) bowl of sugar                           e) crucible of magnesium oxide

b) shaker of salt                          f) air bag full of nitrogen gas

c) bottle of water                         g) Neon sign

d) He filled balloon                     h) copper pipe


C. Mole Conversions

1. Given Moles, Convert to Grams


There are three steps to converting moles of a substance to grams:

1. Determine how many moles are given in the problem.
2. Calculate the molar mass of the substance.
3. Using dimensional analysis: Multiply step one by step two.

Example: A laboratory procedure needs 0.10 moles of Mg ribbon.  How much Mg 

ribbon should you use?

 

 


More Examples:
Calculate how many grams are in 0.700 moles of H2O2












Example:
Convert 2.50 moles of KClO3 to grams










2. Given Grams, Convert to Moles

Three steps:

1) Determine how many grams are given in the problem.
2) Calculate the molar mass of the substance.
3) Use dimensional analysis to setup solution.

Example: A jug of distilled water contains one liter or 1000.0 grams.

How many moles is this?

 

 


More Example:
Convert 25.0 grams of KMnO4 to moles
















Example:
Calculate how many moles are in 17.0 grams of H2O2










3. How many Representative Particles (Atoms or Molecules or Formula Units) ?

Three steps:
1)Determine how many moles are given in the problem.
2)Use the relationship: 6.02 x 1023 representative particles = 1 mole
3)Use dimensional analysis to setup the problem.
Example:  Propane (C3H8) is a gas used for cooking and heating.  How many
  molecules are in 2.12 mol of propane?

 

 

More examples:
How many moles is 2.80 x 1024 atoms of silicon?

 

 

How many moles is 2.17 x 1023 molecules of bromine?

 

 

 

 

 

4)



III. Using the Percent Composition to find the EMPIRICAL 
FORMULA and the MOLECULAR FORMULA

A. Finding the Empirical Formula


_________________ - lowest whole number ratio of the atoms of the elements in a compound

Example:      H2S

. the subscripts: ________ for H tell us the ___________ of atoms in one molecule
                        ________ for S

                        _____ atoms H : _____ atom S

. in a larger sample: more atoms are present, but still in a ____ : _____atom ratio


                      50,000 atoms H :  ______________ atoms S 

                 or ______________ atoms H : 6.02 x 1023 atoms S

. using the mole:    the  ____________ equals the ___________ equals                 the  _____________ in the formula


To find the Formula (subscripts) of a compound:

1) Convert the _____________ of each element present to __________


2) Change the moles to a _______________: ___________________________

_______________________________________________________________


3) Use this mole ratio as the ____________________ in the formula



Example: A compound contains 40.0 g of C, 6.70 g of H and 53.30 g of O. Find the empirical formula.















Example: A compound contains 1.10 g of Cr and .51 g of O. Find its formula.














Example: A compound contains 43.6% P and 56.4% O. Find its formula.

The data is given in percents! Assume you have a 100 g sample and convert the percents to grams.


 

 

 

 

 


B. Find the MOLECULAR FORMULA

_______________ - a chemical formula that shows the actual number and kinds of atoms present in a molecule of a compound

. many molecules contain a ratio of atoms that is some multiple of the empirical formula

. for example, butane molecules are C4H10 not C2H5

. to find the true formula: 1) find the empirical formula 2) need the mass of the actual formula (Formula Weight)
























 
HOMEPAGE