Tasnima Farin
April 22 2014
Mole Day/ Fun with Moles
The Mole:
The mole is defined as a unit of measurement to measure the amount of matter in a substancei.e. 16.1 mole of Carbon; means that the amount of carbon in the sample is 16.1 mol
1 mol of substance contains (6.022)(1023) particle (atoms, molecules, etc.)
(6.022)(1023) is a special number, called Avogadro’s Number (Named after the man who
discovered it)
Examples: 1 mol of Al contains (6.022)(1023) atoms
1 mol of S8 contains (6.022)(1023) molecules
1 mole of NaCl contains (6.022)(1023) Formula Units
The amount of matter in moles is directly related to the number of particles( atoms, molecules,
etc.) in a sample of matter
Therefore we gather this equation:
Number of moles= (Number of atoms, molecules, or Formula Units)/(Avogadro’s number)
This is shortened to n=N/NA
“n” is number of moles in mol
“N” is Number of atoms, molecules, or Formula Units
“NA” is Avogadro’s Number (6.022)(1023)
1 mole of any substance has a mass in grams equal to its weighted average atomic mass (given on
periodic table), don’t forget to calculate for total atomic mass of the substance by adding up all the
atomic masses of each atom(s)
Therefore we can we can gather another equation:
Number of moles= (Entire mass of substance)/(Total Atomic mass of entire substance)
Shortened to n=m/MM
“n” is moles in mol
“m” is mass in grams(g)
“MM” is the total atomic mass of substance, also known as molar mass, is measured in grams per
mole (g/mol), and is found by adding up all the atomic masses for each atom(s) in a moleculeTip : From n=N/NA and n=m/MM we can derive the formula N/NA= m/MM
The steps you should follow:
1.
2.
3.
4.
5.
Now we are ready to solve problems using the factor label method. The steps involved are:
Write down the desired quantity/units
Equate the desired quantity to given quantity
Determine what conversion factors you can use (both universal and question specific)
Multiply given quantity by the appropriate conversion factors to eliminate units you don’t want
and leave units you do want.
6. Complete the math
7. You can also use formulas to solve these problems. However, using the factor label method will
make it easier to catch your mistakes.
Examples:
Question # 1
How many atoms are present in 35.4 grams of Cu?
Mass of Cu = 35.4 g
Molar mass of Cu = 63.5 g / mol
Avogadro’s number = ( 6.02)(1023) atoms
# atoms = 35. 4 g Cu x 1 mol Cu x (6.02)(1023)
63.5 g Cu
1 mol Cu
= 3.4 x 10 23 atoms Cu
Question # 2
A chemical reaction requires 3.000 moles of sodium chloride. How many grams is this?
Molar mass of NaCl = ( 22.989 + 35.453)
= 58.44 g/mol
Mass of NaCl = 3.000 mol
Avogadro’s number = ( 6.02)(1023) atoms
g of NaCl = 3.000 mol NaCl x 58.44 g NaCl
1 mol NaCl
=
175.3 g NaCl
Textbook Summary:
o The molar mass and average atomic mass of an element is numerically the same. This value is
given on the periodic table.
o The molar mass of a compound is the sum of the molar masses of each entity in the compound.
o Molar mass is the mathematical link between the amount in moles and mass in grams.
o The number of atoms or ions in a sample of a compound equals the number of atoms or ions per
molecule or formula units times the number of molecules or formula units in the sample.
Homework:
P. 275 - 282- Avogadro’s Number and Molar Mass
Finish all the worksheets, P.277 # 1- 2, # 4-12; P. 280 # 1 – 4; P.283 # 4-6
Extra Practice:
http://misterguch.brinkster.net/PRA010.pdf
http://pobchemteam.weebly.com/uploads/2/5/7/7/25772138/mole_conversion_problems_key.pdf
https://www.youtube.com/watch?v=e_KMPemSVPc