unit 5 moles and stoichiometry lesson 2: the molar relationships
TRANSCRIPT
Unit 5
Moles and Stoichiometry
Lesson 2:The Molar Relationships
Molar Relationships
• We can convert between moles, NA, molar mass and volume using molar relationships and dimensional analysis.
• Relationships:
grams and moles
grams and representative particles
moles and representative particles
moles and liters
How to solve Molar Conversion Problem?
Molar conversions require the use of a problem solving process called dimensional analysis.
Method of calculation utilizing a knowledge of units.
Given units can be multiplied or divided by a factor to give the desired units.
How to solve Molar Conversion Problem?
Conversion factors are used to manipulate units:
Desired unit = given unit (conversion factor)
The conversion factors are simple ratiosos
unitgiven
unit desiredfactor Conversion
Conversion Factors
• ratio that comes from a statement of equality between 2 different units
dollarquarters 14
Example:
statement of equality
conversion factor
quarters
dollar
4
1
dollar
quarters
1
4or
Conversion Factors• can be multiplied by other numbers
without changing the value of the number
quartersdollar
quartersdollars 12
1
43
quarters
dollar
4
1
dollar
quarters
1
4or
How to solve Molar Conversion Problem?
In dimensional analysis always ask three questions:
1. What data are we given?
2. What quantity do we need?
3. What conversion factors are available to take us from what we are given to what we need?
The Four Steps to Solving Mole Problems
• Step 1: Figure out how many parts your calculation will have by using the mole map diagram.
• Step 2: Make a T-chart, and put whatever information the problem gave you in the top left. After that, put the units of whatever you were given in the bottom right of the T, and the units of what you want to find in the top right.
The Four Steps to Solving Mole Problems
• Step 3: Put the conversion factors into the T-chart in front of the units on the right. Use your mole map diagram.
• Step 4: Cancel out the units from the top left and bottom right, then find the answer by multiplying all the numbers on the top together and dividing it by the numbers on the bottom.
Molar RelationshipsGrams and Moles
molar mass
(g/mol)
Mass in Grams
Moles
How many grams of lithium are in 3.50 moles of lithium?
3.50 mol Li
1
= g Li1 mol Li
6.94 g Li24.29
Converting Moles to Grams
Converting grams to moles
How many moles of lithium are in 18.2 grams of lithium?
18.2 g Li
1= mol Li
6.94 g Li
1 mol Li2.62
Converting Moles to Mass in a Compound
• How many grams of calcium chloride are in 0.98moles of calcium chloride?
.98mole CaCl2
110.98g CaCl2
1mole CaCl2
= 108.76 g CaCl21
Molar RelationshipRepresentative Particles and Moles
MOLES
6.02 1023
(particles/mol)
NUMBER
OF
PARTICLES
NUMBER
OF
PARTICLES
Converting Moles to Number of representative particles
1. How many molecules are in 2.50 moles of C12H22O11?
2.50 mol6.02 1023
molecules
1 mol= 1.51 1024
molecules C12H22O11
2. How many atoms of lithium are in 3.50 moles of lithium?
3.50 mol Li = atoms Li
1 mol Li
6.02 x 1023 atoms Li 2.11 x 1024
Calculate the moles of Aluminum Oxide in 2.0 x1024 Formula Units
2.0 x 1024
formula units
= 3.32 mole of Aluminum Oxide6.02 1023
Formula units
1 mole
Converting Number of RepresentativeParticles to mole
Molar RelationshipGrams and Representative Particles
molar mass
(g/mol)
MASS
IN
GRAMS
MOLESNUMBER
OF
PARTICLES
6.02 1023
(particles/mol)
Molecules to Grams
• Find the mass of 2.1 1024 formula units of NaHCO3.
2.1 1024
Formula units
1
1 mol NaHCO3.
6.02 1023
Formula units
= 293.06 g NaHCO3
2.9x102
84.01 g
1 mol
Grams to Molecules
• Find the number of formula units in 5 grams of MgSO4.
5 gramsMgSO4
1
1 molMgSO4
120.37g
= 2.50 1022 formula units MgSO4
6.02 1023
Formula units
1 mol
Molar RelationshipsVolume and Moles
Molar volume
(22.4 L/mol)
volume Moles
Avogadro’s Law
• equal volumes of gases at the same Temperature and Pressure contain equal numbers of molecules
• at same T and P, volumes varies directly with number of moles (n)
Molar Volume of Gases
Molar Volume of Gases
• like molar mass– mass of one mole of substance
• but with volume– volume of one mole of substance
• because of Avogadro’s law, one mole of any gas has the same volume as any other gas at the same T and P
Molar Volume of Gases• Standard Temperature and Pressure
– STP– 1 atm and 0°C
• Standard Molar Volume of Gas– volume of one mole of gas at 1 atm and 0°C
is 22.4L
• 22.4 L of any gas has one mole of particles but has different masses
A chemical reaction produces 0.0680 mol of oxygen gas.
What volume in liters is occupied by this gas sample at STP?
0.068 mol of O2
= 1.52L O2
1 mol O2
22.4L O2
Molar Volume Problems
Molar Volume Problems
• How many moles of Oxygen gas are in 112.00L Oxygen at STP?
112.00L
1 22.4L
1 mol= 5.0 mol Oxygen gas
Volume to Mass• A chemical reaction produced 98.0 mL of
sulfur dioxide gas at STP. What was the mass of gas made?
gmol
g
L
mol
mL
LmL 280.0
1
06.64
4.22
1
1000
10.98