Moles Videodisk Unit 4

Moles 1 mole of a substance contains 6.022 x 1023 particles So a “mole” is a number, very similar to a dozen. A dozen = 12 A mole (mol) = 6.022 x 1023 It can be found in your reference packet on page one Avogadro’s number = 6.022 x 1023 Moles are similar to a pair(2) of dozen(12). See attached page for examples of a mole.

Meaning of Avogadro’s Number (The mole) The mole (abbreviated mol) is the base unit for measuring the amount of a substance. The definition of a mole comes from how many particles (atoms, in this case) there is in exactly 12 grams of Carbon-12. Through many years of experimentation, it has been confirmed that a mole of any substance has 6.022*1023 representative particles

Molar Mass or Gram Formula Mass (GFM) or Formula Weight Molar Mass = the mass of 1 mole of a substance in grams (also known as Gram Formula Weight or Formula Weight) mass given on periodic table is in amu Because amu and grams are relative we can say the masses on the periodic table are in grams To find molar mass add all the atomic masses of the elements in the compound.

Practice – Find the molar mass of: MgCl2 Ca(OH)2 C6H12O6 Answers: 95.21 g/mol, 74.10 g/mol, 180.16 g/mol If the molar mass is the final answer to a question, then the significant figures for adding measurements rule should be invoked. If it’s a step along the way, then keep the extra decimal place.

Moles are the central unit in chemistry. They allow us to change units between: Mass Number of particles (atoms or molecules or formula units or particles) Volume Moles are a name for a group. pair = 2 dozen = 12 mole = 6.02 x 1023

Moles and Mass The conversion factor is 1 mol = Molar Mass (or GFM or FW) Convert 5.0 moles of Sulfur to grams

Sample Problem 606 g Zn(NO3)2 To carry out a chemical reaction you need 3.20 moles of zinc nitrate Zn(NO3)2. What is the mass of 3.20 moles of Zn(NO3)2? 606 g Zn(NO3)2

Moles and Particles The conversion factor is 1 mol = 6.022 x 1023 particles (molecules, atoms, etc) Convert 2.0 moles H2O to molecules 1.2 x 1024 mc H2O

Convert 4.3 mol of O2 gas at STP to liters Moles and Liters of Gas The conversion factor is 1 mol = 22.4 L It only applies to Gas at STP (standard temperature and pressure) which is 0 degrees C and 1 atm Convert 4.3 mol of O2 gas at STP to liters

Sample Problem 1.45 mol CaCO3 A piece of marble contains 8.74 x 1023 formula units of calcium carbonate. How many moles of CaCO3 is that? 1.45 mol CaCO3

Hall Analogy M O L E S Mass Molecules Liters (of Gas At STP) 1 mole = 22.4 L M O L E S Mass Molecules 1 mole = 6.022 x 1023 particles 1 mole = GFM You must enter the hall to get to the other rooms.

Traffic Circle Analogy To get to volume, mass, or particles, you have to pass through the mole!

Sample Problem You need 250 grams of table sugar, or sucrose (C12H22O11), to bake a cake. How many sucrose molecules will be in the cake? 4.4 x 1023 molecules C12H22O11

Sample Problem If you burned 4.00 x 1023 molecules of natural gas, or methane (CH4) during a laboratory experiment, what mass of methane did you burn? 10.7 g CH4

Finding Molarity from Grams of Solute What is the molarity of 100.0 ml of a sodium chloride solution that has 30.56 grams of solute dissolved in it? Convert grams to moles Convert mL of solution to L Use M = mol/L (found in reference packet) to solve for molarity. This was part of Unit 2, but now the skill of converting to moles first can be included in problems. Answer: 5.229 mol/L or 5.229 M

More Solution Examples How many grams of potassium iodide are in 250.0 ml of a 0.50 M solution? Answer: 21 g A 0.75 M solution has 45.62 grams of sodium nitrate dissolved in it. What is the volume of the solution? Answer: 0.72 L