Unit 5 Moles and Stoichiometry Lesson 2: The Molar Relationships
Molar Relationships We can convert between moles, N A, 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) os The conversion factors are simple rati os
Conversion Factors ratio that comes from a statement of equality between 2 different units Example: statement of equality conversion factor or
Conversion Factors can be multiplied by other numbers without changing the value of the number or
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 Relationships Grams 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 Li 1 mol Li 6.94 g Li 24.29 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 Li 2.62
Converting Moles to Mass in a Compound How many grams of calcium chloride are in 0.98moles of calcium chloride?.98mole CaCl 2 110.98g CaCl 2 1mole CaCl 2 = 108.76 g CaCl 2 1
Molar Relationship Representative Particles and Moles MOLES 6.02 10 23 (particles/mol) NUMBE R OF PARTIC LES NUMBER OF PARTICLES
Converting Moles to Number of representative particles 1. How many molecules are in 2.50 moles of C 12 H 22 O 11 ? 2.50 mol 6.02 10 23 molecules 1 mol = 1.51 10 24 molecules C 12 H 22 O 11
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 10 23 atoms Li 2.11 x 10 24
Calculate the moles of Aluminum Oxide in 2.0 x10 24 Formula Units 2.0 x 10 24 formula units = 3.32 mole of Aluminum Oxide 6.02 10 23 Formula units 1 mole Converting Number of Representative Particles to mole
Molar Relationship Grams and Representative Particles molar mass (g/mol) MASS IN GRAMS MOLES NUMBER OF PARTICLES 6.02 10 23 (particles/mol)
Molecules to Grams Find the mass of 2.1 10 24 formula units of NaHCO 3. 2.1 10 24 Formula units 1 1 mol NaHCO 3. 6.02 10 23 Formula units = 293.06 g NaHCO 3 2.9x10 2 84.01 g 1 mol
Grams to Molecules Find the number of formula units in 5 grams of MgSO 4. 5 grams MgSO 4 1 1 mol MgSO 4 120.37g = 2.50 10 22 formula units MgSO 4 6.02 10 23 Formula units 1 mol
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
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 O 2 = 1.52L O 2 1 mol O 2 22.4L O 2 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?