Download Slide 1 - Midland ISD

Math in Chemistry
Examples and Memory
Tricks
Limiting Reactants
79.1 g of zinc react with 0.90 L of HCl. Identify the
limiting and excess reactants. How many liters
of hydrogen are formed at STP?
Zn + 2HCl
79.1 g
0.90 L

ZnCl2 + H2
?L
Limiting Reactants
Zn + 2HCl
79.1 g
79.1
g Zn

ZnCl2 + H2
0.90 L
?L
1 mol
Zn
1 mol
H2
22.4 L
H2
65.39
g Zn
1 mol
Zn
1 mol
H2
= 27.1 L
H2
Limiting Reactants
Zn + 2HCl
79.1 g
0.90
L HCl

ZnCl2 + H2
0.90 L
?L
1 mol
HCl
1 mol
H2
22.4 L
H2
22.4
2 mol
HCL
1 mol
H2
L HCl
= 0.45 L
H2
Limiting Reactants
Zn: 27.1 L H2
HCl: 0.45 L H2
Limiting reactant: HCl
Excess reactant: Zn
Percent Yield
 When 45.8 g of K2CO3 react with excess
HCl, 46.3 g of KCl are formed. Calculate
the theoretical and % yields of KCl.
K2CO3 + 2HCl  2KCl + H2O + CO2
Mass-Mass Stoichiometry
The reaction of fluorine with ammonia
produces dinitrogen tetrafluoride and
hydrogen fluoride.
5F2 + 2 NH3 → N2F4 + 6HF
1. How many grams of NH3 are
required to produce 7.38g HF?
2. How many grams of N2F4 can be
produced from 265g F2?
Mole-Mole Examples
Isopropyl alcohol (C3H7OH) burns in the air to this equation:
2C3H7OH + 9O2 → 6CO2 + 8H2O
 Write the equation.
 Calculate the mass of oxygen needed
to react with 3.40 moles of isopropyl
alcohol.
 Find the moles of water when 6.20
mol O2 reacts with C3H7OH.
Formulas to Use
Mole - Mole
Known
mol of unknown
mol of known
Mol Ratio – from equation
Mass - Mass
Known g
1 mol known
molar mass known
Other
mol of unknown
molar mass unknown
mol of known
1 mol unknown
OR
OR
6.02 × 1023 particles
Known L
1 mol known
mol of unknown
22.4 L unknown OR
particles
22.4 L known
mol of known
1 mol unknown
6.02 × 1023 particles