Arnoldi / Lazaar
Chem Com
Unit Two Section C
Notes
I. Keeping Track of Atoms
A. The Law of Conservation of Mass
1. DefinitionIn a chemical reaction, mass cannot be
______or ______.
2. Differentiating between Coefficients and Subscripts
a. Coefficients______before the formula
in general, coefficients represent the ______
specifically, coefficients represent:
the number of ______(if the substance is covalent)
covalent substances are made from:
______, ______and ______
ORthe number of ______(if the substance is ionic)
ionic substances are made from:
______and ______
or they contain a ______
but not a polyatomic ion with ______
ORthe number of ______(if you have a singular,
uncharged particle)
COMPLETE PROMPT ONE NOW
b. Subscripts______after the atom
subscripts represent the ______in
______of the substance
Example: Na2O
What kind of compound is this?
What does the “2” tell us?
How many oxygen atoms are there? How do you know?
3. Application to Chemical Equations
a. Because of the Law of Conservation of Mass, all chemical equations must be ______.
In a balanced equation, the number of atoms you start with
must ______the number of atoms that you end with.
b. NOTE: The total number of atoms of an element =
______
COMPLETE PROMPT TWO NOW
C. Modeling Matter
We can show what happened in a reaction via a visualrepresentation. There are three important things to rememberwhen doing this.
1. Any compound must be shown with the atoms ______.
Remember, ______will show us how many atoms to draw in the compound. ( ____ is understood).
2. How many molecules / formula units / atoms of each species
that you draw is shown by the ______.
3. When you are finished, you should have drawn
______number of atoms of eachelement on both sides of the equation.(they will just be rearranged differently).
EXAMPLEAnswer the following questions regarding this chemical reaction: 2 A2B3 4 A + 3 B2
a. What is the subscript on element B on the reactant side?
b. What is the coefficient on element B on the reactant side?
c. So, how many atoms of element B reacted?
d. Show what this reaction would look like on the atomic level.
COMPLETE PROMPT THREE NOW
II. Accounting for Atoms / Balancing Chemical Equations
A. Definitions
1. Coefficients and Subscripts (review)
Coefficients: ______
(representing: ______)
______are generic, and can be used for
any type of particle.
Atoms : singular (by themselves), uncharged particles
Formula Units:ionic particles
Molecules:covalent particles(hydrogen, nonmetals, or semi-metals in any combo)
Subscripts: ______
(representing the number of______)
B. Balancing Chemical Equations
1. Steps
a. Make a Chart (______)
b. Number of Atoms on the Left ______Number of Atoms on the Right. Remember, number of atoms =
______. (______)
c. Add or change ______(never______).
2. Helpful Hints
a. Polyatomic Ions… if you see the same polyatomic ion on both sides of the equation, count the entire polyatomic ion together, rather than its separate atoms separately.
How do we count poly ions? ______
ex: Ca(ClO3)2
HNO3
b. Water… is really HOH not H2O, so count it as a H and OH if______
c. Combustion Equations
Acombustion reaction is a reaction in which a CH or a CHO compound combines with O2. For example:
___CH (or CHO) + ___O2 ___CO2 + ___H2O
Balance it in this order…
Skip CH (or CHO) + 3rd O2 2nd CO2 + 1st H2O
1st: Balance the ______
2nd: Balance the ______
3rd: Balance the ______
Last: ______
C. Examples
___H2O___H2+ ___O2
___K+___Cl2___KCl
___Cd+2 + ___ HNO3 ___ Cd(NO3)2 + ___H2
__ Al(OH)3(aq) + __ H3PO4(aq) __ AlPO4 + __ H2O
___ C3H8 + ___ O2 ___ CO2 +___ H2O
COMPLETE PROMPT FOUR NOW
IV. The Mole
A. Definition (Avogadro's Number)
The number of particles equal to the ______.
(______)
B. Basic Math Problems
1. Molar Mass
a. Definitionthe mass of ______of particles
(the mass, in grams, of 6.02 X 1023 particles)
b. Different Types of Molar Mass
Atomic Mass(the particle is an ______)
The mass of asingle atom.
(______)
Formula Mass(the particle is a formula unit)
The mass of an ionic compound.
(______)
Molecular Mass(the particle is a ______)
The mass of a covalent compound.
(______,
including ______).
Examples
What is the mass of each of the following?
Classify it as an atomic, molecular or formula mass.
* round to one decimal place from the periodic table
*if there is more than one type of atom, ADD everything
Lithium
(by itself)
CCl4
(combination of nonmetals) -> covalent
Sr(OH)2
(polyatomic ion) -> ionic
COMPLETE PROMPT FIVE NOW
- Converting Among Units– One Step Problems
Mole Map
Volume calculations can only be done for a substance in the ______at ______.
STP =
1 mole = _____
and
1.00 atm (P) / 0’C (T)
1 mole = ______
1 mole = ______
Particle Types:
atom – ______
formula unit – ______molecule – ______
Ion – ______
What Steps will you use to complete these problems?
1. Put the ______.(include ______).
2. Leave Spacethen, write ______
3. Determine the ______you need.
# fraction lines needed = ______
4. Fill in the ______ONLY.
current numerator becomes ______
next numerator is determined by ______
5. Fill in the ______. Do the math.
the numbers come from the ______
Examples
How many moles of Ca(ClO3)2 are in 46.7 grams?
There is a sample of matter containing 3.6 X 1025 formula units of Calcium Chloride. (CaCl2). Why are these called formula units? How many moles is this?
What volume would 6.5 moles of H2 Gas occupy at STP?
COMPLETE PROMPT FIVE NOW
3. Converting Among Units – Two Step Problems
Examples:
1.75 X 1024 atoms of Ca is equal to what mass of Ca?
Why did we say “atoms”?
What is the mass of 3.45 L of Neon gas at STP?
COMPLETE PROMPT SEVEN NOW
C. Moles and Equation Math Examples
Expanded Mole Map
1 mole = 22.4 L 1 mole = 22.4L
1 mole = PT (g) # of moles 1 mole = PT (g) =
coefficients from balanced equation
1 mole = 6.02 X 1023 particles 1 mole = 6.02 X 1023particles
Examples: C3H8+ 5 O2 3 CO2 +4 H2O
This meansC3H8 O2 CO2 H2O are involved in this reaction in a 1 : 5 : 3 : 4 ratio.
1. Converting Moles GIVENto Moles FIND
If five moles of oxygen react, how many moles of water are made?
using ratios:
using mole math:
If 10 moles of oxygen react, how many moles of waterare made?
using ratios:
using mole math:
(EQN)C3H8+ 5 O2 3 CO2 +4 H2O
If 0.875 moles of oxygen react, how many moles of waterare made?
using ratios:
using mole math
If 1.5 moles of carbon dioxide are made, how many moles of propane (C3H8) reacted?
using ratios:
using mole math:
COMPLETE PROMPT EIGHT NOW
COMPLETE PROMPT NINE NOW
2. Other Stoichiometry Problems
a. Mass Givento Moles Find
Oxygen and hydrogen gases react, by the unbalanced reaction shown below, to form water.
If 3.5 grams of oxygen react, how many moles of water are made?
___ O2 + ___ H2 ___ H2O
b. Particles Given to Volume Find
If 6.58 X 1024 molecules of propane combust by the following balanced reaction, what volume of water will be made?
(assume gas at STP)
C3H8+ 5 O2 3 CO2 +4 H2O
V. Composition of Materials
A. Percent Composition
1. Equation
2. Example
What is the percent composition for each element inFe(IO3)2?
FIRST: find the mass of the compound
SECOND: Use the equation above. Be sure to account for subscripts!
% Iron
% Iodine
% Oxygen
A good check is… do all the percents add up to a number between 99.9 and 100.1?
If yes, you are probably correct.
B. Diagram for Percent Composition in an ore (p. 168)
Which of the samples below is a better source for metal, M? Why?
Site ASite B
Site ASite B
COMPLETE PROMPT TEN NOW