Download 5 6. moles and rxn - New Hartford Central Schools

Mole
Moles
How a chemist measures the amount of matter in a substance
counting unit - number of molecules ; atoms ; particles
MOLE TRIANGLE
Way to convert
Road Map – map out
where you start to where
you end
Conversions are along
side the arrows
How?
Divide in ()
Multiply out (x)
22.4 L
Volume
Grams
Formula wt. or
gram-form. mass
MOLES
6.02 x 1023
# molecules or
# particles
Moles
How many moles of oxygen in
1 mole of Al2(SO4)3?
3 x 4 = 12
(the parantheses are
Like a distribution in math)
How many moles of oxygen in
1 mole of CuSO4  5H2O?
4
+ (5 x 1) = 9
Gram atomic/formula mass (molecular mass)
= mole of substance
Al2(SO4)3
Al 2
2 x 27
= 54
S
3
3 x 32
= 96
O 12
12 x 16
= 192
Gram form mass is the sum
of the total mass of each
element in the formula
Add all the masses up
54+96+192 = 342 g/mol
Avogadro’s Number
Volume of Gas at STP
6.02 x 1023
1 mole = 22.4 L
Atoms / mole
Percent Composition
“ parts per hundred”
divide the quantity under consideration by the total quantity involved
Part
x 100
whole
Table T
For any % composition problem--you must first find the formula mass of
the compound
What is the percent by
mass of chlorine in CaCl2?
Part
x 100
whole
2Cl X 100
CaCl2
2(35.45)
110.98
X 100
% Cl = 63.89%
What is the percent by mass
of water in Na3PO4 •12H2O ?
What is the percent by mass
of water in hydrate:
Mass of hydrate:
132.4g
Mass of anhydrous
124.2g
Find the formula mass first
3 x 23 = 69
1 x 31 = 31
4 x 16 = 64
+ Mass of water
To find mass of water Subtract the two #’s
12 x 18 = 216
Add them all up
69+31+64+216 = 380 g/mol
Now find %
216 g/mol
X 100 =56.8 %
380 g/mol
132.4 -124.2 = 8.2 g
Now find %
8.2 g X 100 = 6.2 %
132.4 g
Empirical Formula
the simplest integer ratio in which
atoms combine to form a compound
75 % C and 25% H
What is the empirical formula?
1. Change % to grams
75g
1. Change % to grams
75g
2. Find number of moles
12g
2. Find number of moles
3. Divide by the smallest number
6.25
4. find ratio (becomes the subscripts) 3. Divide by the smallest number
6.25
5. Write the formula
6.25
4. find ratio
1 to 4
5.formula
Molecular Formula
the actual ratio of
the atoms in a
molecule
1. Write down your given
2. Find the molecular mass
of the compound
3. Divide the mass given in
the problem by the
Molecular mass
4. Multiply subscripts by
Answer to step 2
CH4
The molecular mass of a
compound with an empirical
formula of CH2 is 28g, what
is the molecular formula?
1. Find formula
12 + 2(1) = 14 g/mol
mass
2.
28g
=2
14 g/mol
3. C2H4
25g
25g
1g
25
25
6.25
Density
D= M
V
For a gas at STP
Table T :
D = Formula wt
22.4L
CO2 =
[12 + 2(16)]
22.4 L
Reactions
Chemical Reaction
Chemical sentence that describes a reaction
Reactants
Products
+
=
and
Yields
or
produces
Equilibrium- reaction forward and reverse
(s)
solid
(l)
(g)
liquid
gas
(aq)
Solution dissolved in water
heat
D
Pt
Heat was added
catalyst
Balancing Equations
Law of Conservation of Mass-Energy
Mass, energy, & charge are conserved
(MEC)
Balance equations by using coefficients
1. Determine if the reaction is combustion (CxHy +O2
or not
If it is:
CO2 + H2O)
If it’s not:
2. Start with the carbons & make
sure they are the same on both
sides of the arrow.
3. Next balance the H’s
4. Finally balance the O’s- watch out
they are separated on the product side!
2. Find the most complicated formula
3. By inspection use coefficient to
balance atoms (each element!!)
4. Continue to add coefficients until
you have same number on both sides
Check your work!!!!
Hydrogen plus oxygen yields water
H2 + O2 = H2O
OR
H2 + O2
H2O
How many H’s do I have on both sides of the equation? 2
Now, How many O’s do I have on both sides of the equation?
2 on left, 1 on right
Put a 2 as a coefficient in front of the H2O
H2 + O2
2H2O
How does that affect your number of H’s? How do we fix it?
2H2 + O2
2H2O
Place a 2 in front of
The H on left side to balance
Nitrogen plus hydrogen yields ammonia
Look at both sides
N2 + H2
NH3
N2 + 3H2
2NH3
Pick one element and balance firs
Place 2 in front of NH3
Now go back and balance H’s
Types of Chemical Reactions
A compound is burned with oxygen and produces CO2 and H2O. The
compound can contain C, H, & O.
Burning
Incomplete Combustion: CxHy + O2
Complete Combustion: CxHy + O2
Combination of
two separate
things to make
ONE new thing.
CREATE/Construct
2
1
A+B
AB
4Fe+3O2
+
(decompose)
Break apart a
compound into
two or more
things.
Deconstruct
1
AB
2
A+B
Examples
Examples
Sr + I2
Decomposition
SrI2
2Fe2O3
2H2O2
Mg(Cl03)2
2H2O + O2
MgCl2 +
3O2
+
Single
Replacement
An element (all alone
by itself) takes the
place of an element
in a compound to
form a new
compound and a new
element by itself.
Stud kicks out wimp
A + BC
AC + B
Stud meter = Table J
Higher elements replace
lower. Higher elements
are more reactive.
Examples
Mg + H2SO4
F2 + 2NaBr
+
Synthesis
(Combination)
CO + H20
CO2 + H20
MgSO4
+ H2
Br2 + 2NaF
+
Combustion
Double
Replacement
The positive charge
elements swap. Two
new compounds are
formed ONLY IF one
of the new compounds
is insoluble.
Swap Meet
Use TABLE F to
figure out if swap
meet happens.
Innies vs Outies
+-
+-
AB + CD
+-
+-
AD+ CB(s)
Example
CdBr2 + Na2S CdS(s)
+2NaBr
+
+
Mole Mall Expansion
Grams
Grams
Mass PT
Mass PT
Liters
Moles
22.4
Use coefficients
Moles
Set up a proportion
6.02x1023
# particles
Liters
22.4
6.02x1023
# particles