The Mole, Masses, and Percent Composition

Note-taking Worksheet – The Mole, Masses, and Percent Composition The Mole Why is the mole necessary? How does it help connect the particulate and macroscale worlds? Explain how the mole is used as a counting mechanism. How does the egg story provided in the video relate to the molecules/moles story? What is the numerical value for the mole? What types of samples does the mole apply to? What is meant by "units" in the expression for a mole? Why is the identity of the unit able to change rather than just being fixed? How can we use the value of a mole as a PER expression? What units can we move to and from using the mole as our conversion factor? Make sure that you are comfortable using the mole expression both ways. Think about the scale of Avogadro's number. Explain why we use the unit "mole" instead of the actual value for the number of particles. How many atoms are in 7.75 moles of methane (CH 4)? Step 1: What is your given quantity? Step 2: What is your wanted quantity? Step 3: What unit path do you need to take? Step 4: What does your setup look like? Step 5: Calculate your answer. Step 6: Double check your answer. Explain how you are able to double check your answer based on the magnitude of the number. Molecular and Formula Masses What do the subscripts in a formula represent? What do you do if there is a subscript both inside and outside of a parentheses? Review counting the atoms in a formula. Provide a count of all of the atoms present in each of the following compounds. CO MgI2 Ca3(PO4)2 How do you know a compound is ionic? How are the terms molecular mass and formula mass the same? How are they different? Determine the molar masses for both of the following compounds. Respond to the prompts as the video progresses. CO MgI2 Ca3(PO4)2 How is the atomic mass of a compound related to the number of atoms in the compound? How is the atomic mass of a compound calculated? What pieces of information do you need before you are able to calculate the atomic mass? What are the units for molecular and formula mass? Why is it possible to drop all of the decimal places when working with atomic mass? Molar Mass Why do we switch units from amu to g/mol? Review Avogadro’s number. What is this value? Why do we need to use Avogadro’s number? How are molar mass and Avogadro’s number related? (Hint: look at units…) How are molar mass and molecular/formula mass similar? How are they different? When is it acceptable to use the units amu? When is it acceptable to use the units g/mol? What is the molar mass for copper and how do you find it? Write the molar mass per expression. How many moles are present in a sample of 0.750 g of table salt? Given: Wanted: Path: Percent Composition Videos What does it mean to form a compound in fixed ratios? Write a sentence that describes what the percent composition is. Practice: Calculate the percent composition of the elements in CO Provide a mathematical formula for the % composition of carbon How do you calculate your “whole” in the percent composition? How many percentages do you need to calculate here? Why? How can you double check your calculations on these problems? What is the percent composition of the elements? Practice: What is the percent composition of C and O in CO 2? Calculate the percent composition for CO 2. What is the difference between these two calculations CO and CO2? What did we have to take into account in CO2 that we didn’t need to worry about in CO? Practice: Calculate the percent composition of all of the elements in the compound calcium phosphate. Write the formula for calcium phosphate. Calculate the “whole” for this problem. How many % calculations do you have to do for this problem? How do the parentheses work into your % calculations?