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Transcript
** Refer to atomic mass on Periodic Table!!! **
Review
*** a.) 1 a.m.u. = 1/12 the mass of a ____________ atom
b.) subscript = # of ____________.
Eg. How many total atoms in calcium nitrate?
MOLES
* In Chemistry, we count using moles.*
• 1 Mole = 6 x 1023 atoms (particles).
• (1 mole = # of atoms present in 12g of C-12)
Mole vs. Dozen
• To understand “moles” better, we should compare
1 mole and 1 dozen.
• Q.1. How many apples are in 1 dozen?
• Q.2. How many atoms are in 1 mole?
• Q.3. Which has a greater mass, 1 dozen apples
or 1 dozen grapes?
• Q.4. Which has a greater mass, 1 mole of
sodium atoms or 1 mole of mercury atoms?
Many names, same concept!
Mass of 1 Mole =
• “gram atomic mass”,
• “gram formula mass”,
• “molar mass”,
• “formula weight”,
• “gram molecular mass”.
Practice – Use Periodic Table
• Eg.
1.) 1 atom of H = 1 a.m.u.
1 mole of H = 1g.
2.) 1 atom of C = 12 a.m.u.
1 mole of C = 12g.
3.) 1 atom of Mg = _____________
1 mole of Mg = _____________
4.) 2 atoms of Mg (or, “Mg2”) = _______________
2 moles of Mg = ___________
5.) 1 molecule of CO2 = ____________
1 mole of CO2 = ______________
Atomic Mass
• Atomic mass – The sum total mass of all
present atoms (in a.m.u.)
** Always give your answer as specific as the question suggests. **
Atomic Mass
Eg. Give the atomic mass for all of the following to the nearest tenth . . .
1.) KCl
2.) Ca3N2
3.) (NH4)2S
4.) CCl4
Gram formula mass
• Gram formula mass (gfm) (a.k.a. “molecular mass”
or “formula mass”)
• the sum total mass using grams (g) instead of a.m.u.
• (gfm) always equals 1 mole (mol) of a compound
**(gfm = 1 mole)
*** Q.1. How many molecules are in 1 mole?
Practice
Eg. Give a.)the total # of atoms and b.)the gram formula mass
(gfm) for each of the following (round to whole #)
1.) NaCl
2.) F2
3.) K2CO3
4.) Al(OH)3
5.) C6H12O6
Hydrates
• Hydrates:
– Ionic compound with water (H2O) attached.
– Hydrate = crystals that contain water molecules.
– Anhydrous = substance without water molecules.
Hydrates
Q.1 What is the mass of 1 mole of H2O
(the gfm of H2O)?
Q.2 What is the gram formula mass (gfm)
of 5 H2O?
Hydrates
• Give the gram formula mass (gfm) for each of
the following Hydrates:
1.) CuSO4 ∙ 5H2O
2.) NiSO4 ∙ 6H2O
3.) MgCl2 ∙ 2H2O
“ ∙ ” = “+”
Mole-Mass Conversions
Total mass (g) = (# of Moles) x (gfm)
Eg.1 What is the mass of 3 moles of H2SO4?
Total mass = (3 mol)(gfm of H2SO4) =_____________
Eg.2 What is mass of .5 moles of
copper(II) sulfate?
Eg.1 How many moles are there in 88g of CO2?
Step 1: find the gfm of CO2
Step 2: solve the equation
Eg.2 How many moles are there in 72g of CH4
Practice Problems
• 1.) What is the mass of 2 moles of
iron(II) nitrite?
• 2.) How many moles are in 46g H2SO4?
• 3.) What is the mass of 0.5 mol
carbon dioxide?
• 4.) How many moles are in 544g CaSO4?
% Composition
1.) What is the % composition of oxygen in H2O?
2.) What is the % composition of hydrogen in
H2O?
% Composition
• % Composition =
 mass _ of _ part 

 x100%
 Total _ mass 
Eg.1 What is the % composition of
Carbon in CO2?
Step 1: get the gfm of C (“part”)
Step 2: get the gfm of CO2 (“total”)
Step 3: plug into equation and solve.
• Eg.2 Find the % composition of C, H,
and O in C6H12O6.
• Eg.3 What is the % composition of water in
CuSO4 ∙ 5H2O?
• Eg.4 What is the % water in NiSO4 ∙ 6H2O?
What is the % Ni?
The Element Song
The Element Song
Empirical vs. Molecular Formula
Molecular Formula
C6H6
Empirical Formula
CH
CO2
CO2
C6H12O6
CH2O
C2H4
CH2
C6H12O11
C6H12O11
Empirical Formula
Empirical Formula -
• Q. How do we get the Empirical Formula
from the Molecular Formula???
** Fill in the Empirical Formula for each of the following:
Molecular Formula
C2H2
C4H10
C5H10
C5H9
C3H9O3
Empirical Formula
Converting Empirical Formula 
Molecular Formula:
Steps:
1. Identify the mass of the molecular formula (given)
2. Calculate the gfm of Empirical formula.
3. Divide molecular mass (step 1) by empirical
mass (step 2) and record answer.
 molecular _ mass 

x = 
 empirical _ mass 
4. Multiply subscripts of Empirical formula by the
answer in step 3 to get the Molecular formula.
Eg.1:
The molecular mass of a substance is
48 a.m.u. and its empirical formula is CH4.
What is the molecular formula of this
substance?
Eg.2:
What is the molecular formula of a substance with
a molecular mass of 30g and an empirical
formula of CH3?
Eg.3:
A substance has an empirical formula of CH2O
and a molecular mass of 180g. What is the
molecular formula of this substance?
Eg.4:
A substance has an empirical formula of
CO2 and a molecular mass of 44g. What
is the molecular formula of this substance?
Stoichiometry and Balancing Equations
**Chemical Equations – used to represent chemical
reactions.
• In all chemical rxns.,
3 types of Conservation take place:
1.) Mass
2.) Energy (Kinetics)
3.) Charge (#e- lost = #e- gained (Redox.))
**Important . . .
Symbol
, , , and =
Meaning
“yield”; separates
reactants from products
Stoichiometry
** Stoichiometry – branch of chemistry
that deals with the amounts of
substances that enters (reactants)
and leaves (products) a chemical
reaction. **
Stoichiometry
• Coefficients = # moles of a compound
– Eg. 5 _BaCl2 = 5 moles of BaCl2
• Subscripts = # moles of atoms (inside of a
compound)
– Eg. 3 _Al2S3 = ____ moles of the compound Al2S3,
_____ moles of Aluminum atoms and ____ moles
of Sulfur atoms.
Stoichiometry
1.) __ Na + __ O2  __ Na2O
SOC =
2.) __ Al + __ O2  __ Al2O3
SOC =
Stoichiometry
3.) carbon + oxygen  carbon dioxide
SOC =
**Remember “BrINClHOF”!!!**
4.) hydrogen + oxygen  water
SOC =
Stoichiometry
___ AlCl3 + ____AgNO3  ____AgCl + ____Al(NO3)3
Link – Balancing Equations (timed)
Link 2 – Balancing Equations Handout
Stoichiometry
Rule:
1.) If you change any coefficient in a
balanced equation, you MUST change
them all.
2.) To change coefficients, you must
either multiply or divide by a number.
Stoichiometry
Eg.1:
___KClO3  ____KCl + ____O2
How many moles of Oxygen gas will be
produced if you decompose 4 moles of KClO3?
Stoichiometry
Eg.2:
___Zn + ___CuCl  ___ZnCl2 + ___Cu
How many moles of CuCl were used if
10 moles of copper metal were produced?
Stoichiometry
Eg.3:
___ AlCl3 + ____AgNO3  ____AgCl + ____Al(NO3)3
How many moles of aluminum chloride must
you use in the above reaction to produce
1.5 moles of silver chloride?