UNIT 2 PORTFOLIO
COUNTING ATOMS, MOLECULES, AND OTHER ENTITIES
Use the following materials to measure and/or calculate the quantity described in each step
below. Attach a separate piece of paper showing your calculations. Use units and conversion
factors to help you with the calculations. The following will provide with a stepwise order
that will help you with the calculations:
molecules  atoms
mass (g)  moles (mol)
formula units  ions/atoms
Materials:
balance, plastic pipettes, beaker, copper penny, chalk, water
Methods:
1. Calculate the number of moles of water in one drop of water. To start off, determine the
mass of a drop of water by measuring the mass of 50 drops of water.
Ask yourself, what do you need to find?
molecules  atoms
mass (g)  moles (mol)
formula units  ions/atoms
What information do you need?
mass of 50 drops of water
=
mass of 1 drop
=
g
massof 50drops
50
=
g
=
g
To convert mass (g)  moles (mol) you will need the molar mass of water.
MH2O = 2 x MH + MO
= (2 x
+
)
g
mol
UNIT 2 PORTFOLIO
= 18.02
g
mol
conversion factor =
1mol
18.02 g
SO
n of H2O
= mass of 1 drop (g) x conversion factor
=
=
mol
To convert moles (mol)  molecules you will need Avogadro's number.
1 mol of H2O = 6.02 x 1023 molecules of H2O
conversion factor =
SO
N of H2O
6.02  1023 molecules
1mol
= n of H2O x conversion factor
=
=
molecules of H2O
Therefore . . .
2. Assuming that a penny contains only copper, Cu (s), calculate the number of copper atoms
in a penny.
Ask yourself, what do you need to find?
molecules  atoms
mass (g)  moles (mol)
formula units  ions/atoms
What information do you need?
mass of penny
=
g
UNIT 2 PORTFOLIO
To convert mass (g)  moles (mol) you will need the molar mass of copper, Cu.
MCu
g
mol
=
conversion factor =
mol
g
SO
n of Cu
= mass of penny (g) x conversion factor
=
=
mol
You do not need to convert moles to molecules, since you are working with Cu (s) –
atoms of copper. To convert moles (mol)  atoms you will need Avogadro's number.
1 mol of Cu = 6.02 x 10
23
6.02  1023 atoms
conversion factor =
1mol
atoms of Cu
SO
N of H2O
= n of Cu x conversion factor
=
=
atoms of Cu
Therefore . . .
3. You dissolved 3.00 g of calcium chloride, CaCl2 (s) in 200.00 mL of water. Calculate the
number of chloride ions in the salt solution.
Ask yourself, what do you need to find?
mass (g)  moles (mol)
molecules  atoms
formula units  ions/atoms
UNIT 2 PORTFOLIO
What information do you need?
mass of CaCl2 =
g
To convert mass (g)  moles (mol) you will need the formula unit mass of NaCl.
M CaCl2
=
=(
+
)
g
mol
g
mol
=
conversion factor =
SO
n of CaCl2 l = mass of CaCl2 (g) x conversion factor
=
=
mol
To convert moles (mol)  number of formula units you will need Avogadro's number.
1 mol of CaCl2 = 6.02 x 1023 formula units of CaCl2
conversion factor =
SO
N of CaCl2
= n of CaCl2 x conversion factor
=
=
formula units of CaCl2
To convert number of formula units  number of ions look at how many ions there
are in each formula unit.
1 formula unit of CaCl2 contains ___ ions of Clconversion factor =
ionsofCl
formulaunitsCaCl2
UNIT 2 PORTFOLIO
SO
N of Cl- ions = N formula units of CaCl2 x conversion factor
=
ions of Cl-
=
Therefore . . .
4. Measure the mass of a piece of chalk. Use the piece of chalk to write the full names (first
and last) of all your group’s members on the blackboard. Assuming that the chalk is made
entirely of calcium carbonate, CaCO3, calculate the number of oxygen atoms that you used to
write your name.
Ask yourself, what do you need to find?
molecules  atoms
mass (g)  moles (mol)
formula units  ions/atoms
What information do you need?
mass of CaCO3 used
= mass of chalk before writing – mass of chalk after writing
=
g
To convert mass (g)  moles (mol) you will need the molar mass of _________.
M___ =
=
=
g
mol
conversion factor =
UNIT 2 PORTFOLIO
SO
n of CaCO3 =
=
=
mol
To convert moles (mol)  formula units you will need Avogadro's number.
1 mol of CaCO3 = 6.02 x 1023 formula units of ____
conversion factor =
SO
N of CaCO3 =
=
=
formula units of ______
To convert number of formula units  number of atoms look at how many atoms
there are in each formula unit.
1 formula unit of CaCO3 contains ___ atoms of O
conversion factor =
SO
N of O atoms
= N formula units of CaCO3 x conversion factor
=
=
Therefore . . .
atoms of O