Download Guided notes packet - Science With Horne

Unit 7 – The Mole
Lesson 1
Moles





1 mole of any substance contains _______________________________particles.
____________________________________= 6.022 x 1023
So a “mole” is a number, very similar to a _____________________.
A dozen = ______________
A mole (mol) = ____________________
It can be found in ______________________________________________________________.
Meaning of Avogadro’s Number (The mole)



The mole (abbreviated mol) is the base unit for ________________________________________
of a substance.
The definition of a mole comes from how many ________________________(atoms in this case)
there are in exactly 12 grams of ________________________.
Through many years of experimentation, it has been confirmed that a mole of any substance has
___________________________________________________________________.
Molar Mass or Gram Formula Mass (GFM) or Formula Weight




______________________________ = the mass of 1 mole of a substance in grams (also known
as Gram Formula Weight or Formula Weight.)
Mass given on periodic table is in __________________.
Because amu and grams are relative, we can say the masses on the periodic table are in _______.
To find ______________________________ add all the atomic masses of the elements in the
_____________________________.
Practice – Find the molar mass of:

MgCl2

Ca(OH)2

C6H12O6
If the molar mass is the final answer to a question, the then significant figures for adding measurements
rule should be invoked. If it’s a step along the way, then keep the extra decimal place .
Moles are the _____________________________________________________.
They allow us to change units between:
_____________
____________________________________
____________________
Moles and Mass
The conversion factor is 1 mol = ________________________________________________________.
Convert 5.0 moles of Sulfur to grams.
Sample problem:
To carry out a chemical reaction you need 3.20 moles of zinc nitrate Zn(NO3)2. What is the mass of 3.20
moles of Zn(NO3)2 ?
Moles and Particles
The conversion factor is 1 mol = _____________________________ molecules.
Convert 2.0 moles H2O to molecules
Moles and Liters of Gas
The conversion factor is 1 mol = __________________ L. (also on page 1 of ref. pack)
It only applies to Gas at ____________________ (standard temp. and pressure) which is 0 degrees C and
1 atm.
Convert 4.3 mol of O2 to liters
Sample Problem
A piece of marble contains 8.74 x 1023 formula units of calcium carbonate. How many moles is that?
Hall Analogy (sketch the diagram)
To get to volume, mass, or particles, you have to pass through the mole.
Traffic Circle Analogy( sketch the diagram)
To get to volume, mass, or particles, you have to pass through the mole.
Sample problem
You need 250 grams of table sugar, or sucrose (C12H22O11), to bake a cake. How many sucrose molecules
will be in the cake?
Sample problem
If you burned 4.00 x 1023 molecules of natural gas, or methane (CH4) during a laboratory experiment,
what mass of methane did you burn?
Finding Molarity from Grams of Solute
What is the molarity of 100.0 mL of a sodium chloride solution that has 30.56 grams of solute dissolved
in it?
Convert grams to moles:
Convert mL of solution to L:
Use M = mol/L (found in reference packet) to solve for molarity. This was part of Unit 2, but
now the skill of converting grams to moles can be included in problems.
More Solution Examples
How many grams of potassium iodide are in 250.0 mL of a 0.50 M solution?
A 0.75 M solution has 45.62 grams of sodium nitrate dissolved in it. What is the volume of the solution
Lesson 2
Percent Composition and Molecular vs. Empirical Formulas
Percent Composition (always by mass)

Divide mass of each element______________________________________________________.

Can be found _________________________ or ______________________________________.

Can be used to _________________________________________________________________.
Sample Problem
A 0.2370 g sample of an unknown compound is extracted from the roots of a plant. Decomposition of
the sample produces 0.09480 g of carbon. 0.1264 g of oxygen, and 0.0158 g of hydrogen. What is the
percent composition of the compound?
Empirical & Molecular Formulas

___________________________________ is the simplest whole number ratio of a compound.

___________________________________ shows the actual number of atoms in the molecule.

The molecular formula is some ____________________________ of the empirical formula.

Ex.
C6H12O6
is glucose’s molecular formula
It means in one mole of glucose you have _______________________of carbon, ________________of
hydrogen, and ____________________of oxygen.
CH2O
is glucose’s empirical formula. It means glucose has a ratio of :
What is the empirical formula of:

Molecular formula : C25H10O5

Empirical formula :

Molecular formula : N2O6

Empirical formula :
Steps for determining empirical formulas from percents or masses.
Example: a compound is 27.3% C and 72.7% O
1.
Turn percent to mass (if needed). Assume 100 g if a mass isn’t given.
2. Turn mass into moles.
3. Write a formula using the number of moles as subscripts.
4. Divide both by the smallest number of moles (remember the empirical formula is a ratio.)
5. If needed, multiply until all values are whole numbers.

Often you will be close to whole numbers, rarely will it be exact.
Example: If after dividing you had something like _________________ you would multiply everything
by 2, ending up with __________________, meaning your empirical formula would be______________.
Sample problem
A compound with a mass of 24.975 g was analyzed and found to contain 54.0% Ca, 43.1% O, and 2.9%
H (by mass). What is the empirical formula for the compound?
Divide each mole value by the smallest number of moles and write formula.
Sample problem
Determine the empirical formula for a compound containing 2.128 g Cl and 1.203 g Ca.
Sample problem
What is the empirical formula if a compound consists of :
29.1% Na
40.5% S
30.4% O
Determining Molecular Formulas




Find the _______________________________________
Find molar mass of ____________________________________.
Divide molecular mass by molar mass (of empirical formula)
Multiply ______________________________________________________.
You must be given molecular mass in the problem.
Sample problem
Ribose is an important sugar that is found in RNA. Ribose has a molecular mass of 150.0 g and an
empirical formula of CH2O. What is the molecular formula?
Sample problem
Find the molecular formula for a compound that has a mass of 16.1 g and contains 30.4% nitrogen and
69.6% oxygen. The molecular mass of the compound is 92.0 g/mol.
Lesson 3
Hydrates






Ionic compound that has ___________ incorporated into its crystal structure.
Written as _______________________
Read as “Magnesium Sulfate Heptahydrate”
Means for every one MgSO4 you __________________________________________________.
Notice the prefixes we learned for naming covalent compounds are used to tell how many H2O
molecules you have.
If finding the molar mass, include the _____________________!
Hydrate practice
Name the following hydrates and find their molar masses
 CuSO4 ∙ 5H2O

ZnCl2 ∙ 3H2O

Mg(NO3)2 ∙ 4H2O
Determining the formula of a hydrate
Example: Find the formula of a hydrate that is 48.8% MgSO4 and 51.2 % H2O
 Step 1 – assume exactly 100 grams

Step 2 – calculate moles

Step 3 – calculate mole ratio by dividing by smallest number of moles
Example:
A hydrated cobalt (II) chloride sample has a mass of 11.75 g. After being heated (to remove all water) the
mass is 9.25 g. What is the formula for the hydrate?
Example:
Determine the mass percent of the anhydrous portion and the water in the hydrate
Na3PO4 •10H2O